Add js.Batch

Fixes #12626
Closes #7499
Closes #12874

commands/commandeer.go

@@ -455,6 +455,7 @@ func (r *rootCommand) PreRun(cd, runner *simplecobra.Commandeer) error {
 	r.hugoSites = lazycache.New(lazycache.Options[configKey, *hugolib.HugoSites]{
 		MaxEntries: 1,
 		OnEvict: func(key configKey, value *hugolib.HugoSites) {
+			fmt.Println("Evicting HugoSites", key) // TODO1 remove me.
 			value.Close()
 			runtime.GC()
 		},

common/herrors/errors.go

@@ -133,6 +133,21 @@ func IsNotExist(err error) bool {
 	return false
 }
 
+// IsExist returns true if the error is a file exists error.
+// Unlike os.IsExist, this also considers wrapped errors.
+func IsExist(err error) bool {
+	if os.IsExist(err) {
+		return true
+	}
+
+	// os.IsExist does not consider wrapped errors.
+	if os.IsExist(errors.Unwrap(err)) {
+		return true
+	}
+
+	return false
+}
+
 var nilPointerErrRe = regexp.MustCompile(`at <(.*)>: error calling (.*?): runtime error: invalid memory address or nil pointer dereference`)
 
 const deferredPrefix = "__hdeferred/"

common/maps/cache.go

@@ -69,11 +69,14 @@ func (c *Cache[K, T]) Set(key K, value T) {
 }
 
 // ForEeach calls the given function for each key/value pair in the cache.
-func (c *Cache[K, T]) ForEeach(f func(K, T)) {
+// If the function returns false, the iteration stops.
+func (c *Cache[K, T]) ForEeach(f func(K, T) bool) {
 	c.RLock()
 	defer c.RUnlock()
 	for k, v := range c.m {
-		f(k, v)
+		if !f(k, v) {
+			return
+		}
 	}
 }
 

common/maps/scratch.go

@@ -107,6 +107,23 @@ func (c *Scratch) Get(key string) any {
 	return val
 }
 
+// GetOrCreate returns the value for the given key if it exists, or creates it
+// using the given func and stores that value in the map.
+// For internal use.
+func (c *Scratch) GetOrCreate(key string, create func() (any, error)) (any, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if val, found := c.values[key]; found {
+		return val, nil
+	}
+	val, err := create()
+	if err != nil {
+		return nil, err
+	}
+	c.values[key] = val
+	return val, nil
+}
+
 // Values returns the raw backing map. Note that you should just use
 // this method on the locally scoped Scratch instances you obtain via newScratch, not
 // .Page.Scratch etc., as that will lead to concurrency issues.

common/types/closer.go

@@ -19,6 +19,13 @@ type Closer interface {
 	Close() error
 }
 
+// CloserFunc is a convenience type to create a Closer from a function.
+type CloserFunc func() error
+
+func (f CloserFunc) Close() error {
+	return f()
+}
+
 type CloseAdder interface {
 	Add(Closer)
 }

config/allconfig/configlanguage.go

@@ -137,11 +137,11 @@ func (c ConfigLanguage) Watching() bool {
 	return c.m.Base.Internal.Watch
 }
 
-func (c ConfigLanguage) NewIdentityManager(name string) identity.Manager {
+func (c ConfigLanguage) NewIdentityManager(name string, opts ...identity.ManagerOption) identity.Manager {
 	if !c.Watching() {
 		return identity.NopManager
 	}
-	return identity.NewManager(name)
+	return identity.NewManager(name, opts...)
 }
 
 func (c ConfigLanguage) ContentTypes() config.ContentTypesProvider {

config/configProvider.go

@@ -58,7 +58,7 @@ type AllProvider interface {
 	BuildDrafts() bool
 	Running() bool
 	Watching() bool
-	NewIdentityManager(name string) identity.Manager
+	NewIdentityManager(name string, opts ...identity.ManagerOption) identity.Manager
 	FastRenderMode() bool
 	PrintUnusedTemplates() bool
 	EnableMissingTranslationPlaceholders() bool

deps/deps.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"os"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -268,6 +269,20 @@ func (d *Deps) Compile(prototype *Deps) error {
 	return nil
 }
 
+// MkdirTemp returns a temporary directory path that will be cleaned up on exit.
+func (d Deps) MkdirTemp(pattern string) (string, error) {
+	filename, err := os.MkdirTemp("", pattern)
+	if err != nil {
+		return "", err
+	}
+	d.BuildClosers.Add(types.CloserFunc(
+		func() error {
+			return os.RemoveAll(filename)
+		}))
+
+	return filename, nil
+}
+
 type globalErrHandler struct {
 	logger loggers.Logger
 

hugolib/hugo_sites.go

@@ -111,6 +111,10 @@ func (h *HugoSites) ShouldSkipFileChangeEvent(ev fsnotify.Event) bool {
 	return h.skipRebuildForFilenames[ev.Name]
 }
 
+func (h *HugoSites) Close() error {
+	return h.Deps.Close()
+}
+
 func (h *HugoSites) isRebuild() bool {
 	return h.buildCounter.Load() > 0
 }

hugolib/hugo_sites_build.go

@@ -520,8 +520,9 @@ func (s *Site) executeDeferredTemplates(de *deps.DeferredExecutions) error {
 		},
 	})
 
-	de.FilenamesWithPostPrefix.ForEeach(func(filename string, _ bool) {
+	de.FilenamesWithPostPrefix.ForEeach(func(filename string, _ bool) bool {
 		g.Enqueue(filename)
+		return true
 	})
 
 	return g.Wait()

hugolib/integrationtest_builder.go

@@ -83,6 +83,13 @@ func TestOptWithNFDOnDarwin() TestOpt {
 	}
 }
 
+// TestOptWithOSFs enables the real file system.
+func TestOptWithOSFs() TestOpt {
+	return func(c *IntegrationTestConfig) {
+		c.NeedsOsFS = true
+	}
+}
+
 // TestOptWithWorkingDir allows setting any config optiona as a function al option.
 func TestOptWithConfig(fn func(c *IntegrationTestConfig)) TestOpt {
 	return func(c *IntegrationTestConfig) {
@@ -277,8 +284,9 @@ func (s *IntegrationTestBuilder) negate(match string) (string, bool) {
 func (s *IntegrationTestBuilder) AssertFileContent(filename string, matches ...string) {
 	s.Helper()
 	content := strings.TrimSpace(s.FileContent(filename))
+
 	for _, m := range matches {
-		cm := qt.Commentf("File: %s Match %s", filename, m)
+		cm := qt.Commentf("File: %s Match %s\nContent:\n%s", filename, m, content)
 		lines := strings.Split(m, "\n")
 		for _, match := range lines {
 			match = strings.TrimSpace(match)
@@ -288,7 +296,8 @@ func (s *IntegrationTestBuilder) AssertFileContent(filename string, matches ...s
 			var negate bool
 			match, negate = s.negate(match)
 			if negate {
-				s.Assert(content, qt.Not(qt.Contains), match, cm)
+				if !s.Assert(content, qt.Not(qt.Contains), match, cm) {
+				}
 				continue
 			}
 			s.Assert(content, qt.Contains, match, cm)
@@ -306,7 +315,8 @@ func (s *IntegrationTestBuilder) AssertFileContentExact(filename string, matches
 	s.Helper()
 	content := s.FileContent(filename)
 	for _, m := range matches {
-		s.Assert(content, qt.Contains, m, qt.Commentf(m))
+		cm := qt.Commentf("File: %s Match %s\nContent:\n%s", filename, m, content)
+		s.Assert(content, qt.Contains, m, cm)
 	}
 }
 
@@ -443,6 +453,11 @@ func (s *IntegrationTestBuilder) Build() *IntegrationTestBuilder {
 	return s
 }
 
+func (s *IntegrationTestBuilder) Close() {
+	s.Helper()
+	s.Assert(s.H.Close(), qt.IsNil)
+}
+
 func (s *IntegrationTestBuilder) LogString() string {
 	return s.lastBuildLog
 }

hugolib/page__new.go

@@ -174,6 +174,7 @@ func (h *HugoSites) doNewPage(m *pageMeta) (*pageState, *paths.Path, error) {
 			return nil, m.wrapError(err, h.SourceFs)
 		}
 
+		
 		ps := &pageState{
 			pid:                               pid,
 			pageOutput:                        nopPageOutput,

hugolib/pages_capture.go

@@ -149,7 +149,15 @@ func (c *pagesCollector) Collect() (collectErr error) {
 					id.p,
 					false,
 					func(fim hugofs.FileMetaInfo) bool {
-						return true
+						if id.isStructuralChange() {
+							return true
+						}
+						fimp := fim.Meta().PathInfo
+						if fimp == nil {
+							return true
+						}
+
+						return fimp.Path() == id.p.Path()
 					},
 				)
 			} else if id.p.IsBranchBundle() {

hugolib/pagesfromdata/pagesfromgotmpl.go

@@ -245,10 +245,11 @@ func (b *BuildState) resolveDeletedPaths() {
 		return
 	}
 	var paths []string
-	b.sourceInfosPrevious.ForEeach(func(k string, _ *sourceInfo) {
+	b.sourceInfosPrevious.ForEeach(func(k string, _ *sourceInfo) bool {
 		if _, found := b.sourceInfosCurrent.Get(k); !found {
 			paths = append(paths, k)
 		}
+		return true
 	})
 
 	b.DeletedPaths = paths

hugolib/rebuild_test.go

@@ -71,6 +71,18 @@ Foo.
 
 `
 
+func TestRebuildEditLeafBundleHeaderOnly(t *testing.T) {
+	b := TestRunning(t, rebuildFilesSimple)
+	b.AssertFileContent("public/mysection/mysectionbundle/index.html",
+		"My Section Bundle Content Content.")
+
+	b.EditFileReplaceAll("content/mysection/mysectionbundle/index.md", "My Section Bundle Content.", "My Section Bundle Content Edited.").Build()
+	b.AssertFileContent("public/mysection/mysectionbundle/index.html",
+		"My Section Bundle Content Edited.")
+	b.AssertRenderCountPage(1)
+	b.AssertRenderCountContent(1)
+}
+
 func TestRebuildEditTextFileInLeafBundle(t *testing.T) {
 	b := TestRunning(t, rebuildFilesSimple)
 	b.AssertFileContent("public/mysection/mysectionbundle/index.html",

hugolib/site.go

@@ -1513,7 +1513,11 @@ func (s *Site) renderForTemplate(ctx context.Context, name, outputFormat string,
 	}
 
 	if err = s.Tmpl().ExecuteWithContext(ctx, templ, w, d); err != nil {
-		return fmt.Errorf("render of %q failed: %w", name, err)
+		filename := name
+		if p, ok := d.(*pageState); ok {
+			filename = p.pathOrTitle()
+		}
+		return fmt.Errorf("render of %q failed: %w", filename, err)
 	}
 	return
 }

identity/identity.go

@@ -82,9 +82,8 @@ func FirstIdentity(v any) Identity {
 	var result Identity = Anonymous
 	WalkIdentitiesShallow(v, func(level int, id Identity) bool {
 		result = id
-		return true
+		return result != Anonymous
 	})
-
 	return result
 }
 
@@ -308,11 +307,13 @@ type identityManager struct {
 
 func (im *identityManager) AddIdentity(ids ...Identity) {
 	im.mu.Lock()
+	defer im.mu.Unlock()
 
 	for _, id := range ids {
 		if id == nil || id == Anonymous {
 			continue
 		}
+
 		if _, found := im.ids[id]; !found {
 			if im.onAddIdentity != nil {
 				im.onAddIdentity(id)
@@ -320,7 +321,6 @@ func (im *identityManager) AddIdentity(ids ...Identity) {
 			im.ids[id] = true
 		}
 	}
-	im.mu.Unlock()
 }
 
 func (im *identityManager) AddIdentityForEach(ids ...ForEeachIdentityProvider) {

internal/js/esbuild/batch-esm-runner.gotmpl

@@ -0,0 +1,22 @@
+{{ range $i, $e := .Scripts -}}
+  {{ if eq .Export "*" }}
+    {{ printf "import %s as Script%d from %q;" .Export $i .Import }}
+  {{ else }}
+    {{ printf "import { %s as Script%d } from %q;" .Export $i .Import }}
+  {{ end }}
+{{ end -}}
+{{ range $i, $e := .Runners }}
+  {{ printf "import { %s as Run%d } from %q;" .Export $i .Import }}
+{{ end }}
+{{/*  */}}
+{{ if  .Runners }}
+  let scripts = [];
+  {{ range $i, $e := .Scripts -}}
+    scripts.push({{ .RunnerJSON $i }});
+  {{ end -}}
+  {{/*  */}}
+  {{ range $i, $e := .Runners }}
+    {{ $id := printf "Run%d" $i }}
+    {{ $id }}(scripts);
+  {{ end }}
+{{ end }}

internal/js/esbuild/batch_integration_test.go

@@ -0,0 +1,428 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package js provides functions for building JavaScript resources
+package esbuild_test
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+
+	"github.com/bep/logg"
+	"github.com/gohugoio/hugo/hugolib"
+)
+
+// Used to test misc. error situations etc.
+const jsBatchFilesTemplate = `
+-- hugo.toml --
+disableKinds = ["taxonomy", "term", "section", "page"]
+-- assets/js/styles.css --
+body {
+	background-color: red;
+}
+-- assets/js/main.js --
+import './styles.css';
+console.log("Hello, Main!");
+-- assets/js/runner.js --
+console.log("Hello, Runner!");
+-- layouts/index.html --
+{{ $batch := (js.Batch "mybatch" site.Home.Store) }}
+{{ with $batch.Group "mygroup" }}
+ 	{{ with .Runner "run" }}
+		{{ .SetOptions (dict "resource" (resources.Get "js/runner.js")) }}
+	{{ end }}
+	{{ with .Script "main" }}
+		{{ .SetOptions (dict "resource" (resources.Get "js/main.js")) }}
+	{{ end }}
+{{ end }}
+ 
+{{ with (templates.Defer (dict "key" "global")) }}
+	Defer:
+	{{ $batch := (js.Batch "mybatch" site.Home.Store) }}
+	{{ range $k, $v := $batch.Build.Groups }}
+		{{ $k }}:
+		{{ range . }}
+			RelPermalink: {{ .RelPermalink }}
+			Content: {{ .Content | safeHTML }}
+		{{ end }}
+	{{ end }}
+{{ end }}
+`
+
+// Just to verify that the above file setup works.
+func TestBatchTemplateOKBuild(t *testing.T) {
+	b := hugolib.Test(t, jsBatchFilesTemplate, hugolib.TestOptWithOSFs())
+	b.AssertPublishDir("mybatch_mygroup.js", "mybatch_mygroup.css")
+}
+
+func TestBatchErrorScriptResourceNotSet(t *testing.T) {
+	files := strings.Replace(jsBatchFilesTemplate, `(resources.Get "js/main.js")`, `(resources.Get "js/doesnotexist.js")`, 1)
+	b, err := hugolib.TestE(t, files, hugolib.TestOptWithOSFs())
+	b.Assert(err, qt.IsNotNil)
+	b.Assert(err.Error(), qt.Contains, `failed to build Batch "mybatch": failed to compile Script for "mygroup" > "main": resource not set`)
+}
+
+func TestBatchErrorRunnerResourceNotSet(t *testing.T) {
+	files := strings.Replace(jsBatchFilesTemplate, `(resources.Get "js/runner.js")`, `(resources.Get "js/doesnotexist.js")`, 1)
+	b, err := hugolib.TestE(t, files, hugolib.TestOptWithOSFs())
+	b.Assert(err, qt.IsNotNil)
+	b.Assert(err.Error(), qt.Contains, `failed to build Batch "mybatch": failed to compile Runner for "mygroup" > "run": resource not set`)
+}
+
+func TestBatchErrorScriptResourceSyntaxError(t *testing.T) {
+	files := strings.Replace(jsBatchFilesTemplate, `console.log("Hello, Main!");`, `console.flog("Hello, Main!"`, 1)
+	b, err := hugolib.TestE(t, files, hugolib.TestOptWithOSFs())
+	b.Assert(err, qt.IsNotNil)
+	b.Assert(err.Error(), qt.Contains, `failed to build Batch "mybatch": failed to build bundle: "/js/mybatch_mygroup_main.js:2:27": Expected ")" but found end of file`)
+}
+
+func TestBatch(t *testing.T) {
+	files := `
+-- hugo.toml --
+disableKinds = ["taxonomy", "term"]
+disableLiveReload = true
+baseURL = "https://example.com"
+-- package.json --
+{
+  "devDependencies": {
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1"
+  }
+}
+-- assets/js/shims/react.js --
+-- assets/js/shims/react-dom.js --
+module.exports = window.ReactDOM;
+module.exports = window.React;
+-- content/mybundle/index.md --
+---
+title: "My Bundle"
+---
+-- content/mybundle/mybundlestyles.css --
+@import './foo.css';
+@import './bar.css';
+@import './otherbundlestyles.css';
+
+.mybundlestyles {
+	background-color: blue;
+}
+-- content/mybundle/bundlereact.jsx --
+import * as React from "react";
+import './foo.css';
+import './mybundlestyles.css';
+window.React1 = React;
+
+let text = 'Click me, too!'
+
+export default function MyBundleButton() {
+    return (
+        <button>${text}</button>
+    )
+}
+
+-- assets/js/reactrunner.js --
+import * as ReactDOM from 'react-dom/client';
+import * as React from 'react';
+
+export default function Run(modules) {
+	for (const module of modules) {
+		for (const instance of module.instances) {
+			/* This is a convention in this project. */
+			let elId = §§${module.id}-${instance.id}§§;
+			let el = document.getElementById(elId);
+			if (!el) {
+				console.warn(§§Element with id ${elId} not found§§);
+				continue;
+			}
+			const root = ReactDOM.createRoot(el);
+			const reactEl = React.createElement(module.mod, instance.params);
+			root.render(reactEl);
+		}
+	}
+}
+-- assets/other/otherbundlestyles.css --
+.otherbundlestyles {
+	background-color: red;
+}
+-- assets/other/foo.css --
+@import './bar.css';
+
+.foo {
+	background-color: blue;
+}
+-- assets/other/bar.css --
+.bar {
+	background-color: red;
+}
+-- assets/js/button.css --
+button {
+	background-color: red;
+}
+-- assets/js/bar.css --
+.bar-assets {
+	background-color: red;
+}
+-- assets/js/helper.js --
+import './bar.css'
+
+export function helper() {
+	console.log('helper');
+}	
+
+-- assets/js/react1styles_nested.css --
+.react1styles_nested {
+	background-color: red;
+}
+-- assets/js/react1styles.css --
+@import './react1styles_nested.css';
+.react1styles {
+	background-color: red;
+}
+-- assets/js/react1.jsx --
+import * as React from "react";
+import './button.css'
+import './foo.css'
+import './react1styles.css'
+
+window.React1 = React;
+
+let text = 'Click me'
+
+export default function MyButton() {
+    return (
+        <button>${text}</button>
+    )
+}
+	
+-- assets/js/react2.jsx --
+import * as React from "react";
+import { helper } from './helper.js'
+import './foo.css'
+
+window.React2 = React;
+
+let text = 'Click me, too!'
+
+export function MyOtherButton() {
+    return (
+        <button>${text}</button>
+    )
+}
+-- assets/js/main1.js --
+import * as React from "react";
+import * as params from '@params';
+
+console.log('main1.React', React)
+console.log('main1.params.id', params.id)
+
+-- assets/js/main2.js --
+import * as React from "react";
+import * as params from '@params';
+
+console.log('main2.React', React)
+console.log('main2.params.id', params.id)
+
+export default function Main2() {};
+
+-- assets/js/main3.js --
+import * as React from "react";
+import * as params from '@params';
+
+console.log('main3.params.id', params.id)
+
+export default function Main3() {};
+
+-- layouts/_default/single.html --
+Single.
+{{ $r := .Resources.GetMatch "*.jsx" }}
+{{ $batch := (js.Batch "mybundle" site.Home.Store) }}
+{{ $otherCSS := (resources.Match "/other/*.css").Mount "/other" "." }}
+ {{ with $batch.Config }}
+	  {{ $shims := dict "react" "js/shims/react.js"  "react-dom/client" "js/shims/react-dom.js" }}
+      {{ .SetOptions (dict 
+           "target" "es2018"
+           "params" (dict "id" "config")
+		   "shims" $shims
+	     )
+      }}
+{{ end }}
+{{ with $batch.Group "reactbatch" }}
+	{{ with .Script "r3" }}
+		 	{{ .SetOptions (dict
+			 	"resource" $r
+ 				"importContext" (slice $ $otherCSS)
+				"params" (dict "id" "r3")
+               )
+			}}
+	{{ end }}
+	{{ with .Instance "r3" "r2i1" }}
+	 	{{ .SetOptions  (dict "title" "r2 instance 1")}}
+	{{ end }}
+{{ end }}
+-- layouts/index.html --
+Home.
+{{ with (templates.Defer (dict "key" "global")) }}
+{{ $batch := (js.Batch "mybundle" site.Home.Store) }}
+{{ range $k, $v := $batch.Build.Groups }}
+ {{ $k }}:
+ {{ range . }}
+	{{ .RelPermalink }}
+  {{ end }}
+ {{ end }}
+{{ end }}
+{{ $myContentBundle := site.GetPage "mybundle" }}
+{{ $batch := (js.Batch "mybundle" site.Home.Store) }}
+{{ $otherCSS := (resources.Match "/other/*.css").Mount "/other" "." }}
+{{ with $batch.Group "mains" }}
+  {{ with .Script "main1" }}
+	{{ .SetOptions (dict
+			 	"resource" (resources.Get "js/main1.js")
+				"params" (dict "id" "main1")
+            )
+	}}
+  {{ end }}
+  {{ with .Script "main2" }}
+   {{ .SetOptions (dict
+			 	"resource" (resources.Get "js/main2.js")
+				"params" (dict "id" "main2")
+            )
+  }}
+  {{ end }}
+ {{ with .Script "main3" }}
+   {{ .SetOptions (dict
+			 	"resource" (resources.Get "js/main3.js")
+            )
+  }}
+  {{ end }}
+{{ with .Instance "main1" "m1i1" }}{{ .SetOptions (dict "params" (dict "title" "Main1 Instance 1"))}}{{ end }}
+{{ with .Instance "main1" "m1i2" }}{{ .SetOptions (dict "params" (dict "title" "Main1 Instance 2"))}}{{ end }}
+{{ end }}
+{{ with $batch.Group "reactbatch" }}
+ 	{{ with .Runner "reactrunner" }}
+		{{ .SetOptions ( dict "resource"  (resources.Get "js/reactrunner.js") )}}
+	{{ end }}
+	{{ with .Script "r1" }}
+		{{ .SetOptions (dict
+			"resource" (resources.Get "js/react1.jsx")
+			"importContext" (slice $myContentBundle $otherCSS)
+			"params" (dict "id" "r1")
+			)
+		}}
+	{{ end }}
+	{{ with .Instance "r1" "i1" }}{{ .SetOptions (dict "params" (dict "title" "Instance 1"))}}{{ end }}
+	{{ with .Instance "r1" "i2" }}{{ .SetOptions (dict "params" (dict "title" "Instance 2"))}}{{ end }}
+	{{ with .Script "r2" }}
+		{{ .SetOptions (dict
+			"resource" (resources.Get "js/react2.jsx")
+			"export" "MyOtherButton"
+			"importContext" $otherCSS
+			"params" (dict "id" "r2")
+			)
+		}}
+	{{ end }}
+	{{ with .Instance "r2" "i1" }}{{ .SetOptions (dict "params" (dict "title" "Instance 2-1"))}}{{ end }}
+{{ end }}
+ 
+`
+
+	b := hugolib.NewIntegrationTestBuilder(
+		hugolib.IntegrationTestConfig{
+			T:               t,
+			NeedsOsFS:       true,
+			NeedsNpmInstall: true,
+			TxtarString:     files,
+			Running:         true,
+			LogLevel:        logg.LevelWarn,
+			// PrintAndKeepTempDir: true,
+		}).Build()
+
+	fmt.Println(b.LogString())
+
+	b.AssertFileContent("public/mybundle_reactbatch.css",
+		".bar {",
+	)
+
+	// Verify params resolution.
+	b.AssertFileContent("public/mybundle_mains.js",
+		`
+var id = "main1";
+console.log("main1.params.id", id);
+var id2 = "main2";
+console.log("main2.params.id", id2);
+
+# Params from top level config.
+var id3 = "config";
+console.log("main3.params.id", id3);
+`)
+
+	b.EditFileReplaceAll("content/mybundle/mybundlestyles.css", ".mybundlestyles", ".mybundlestyles-edit").Build()
+	b.AssertFileContent("public/mybundle_reactbatch.css", ".mybundlestyles-edit {")
+
+	b.EditFileReplaceAll("assets/other/bar.css", ".bar {", ".bar-edit {").Build()
+	b.AssertFileContent("public/mybundle_reactbatch.css", ".bar-edit {")
+
+	b.EditFileReplaceAll("assets/other/bar.css", ".bar-edit {", ".bar-edit2 {").Build()
+	b.AssertFileContent("public/mybundle_reactbatch.css", ".bar-edit2 {")
+}
+
+// TODO1 move this.
+func TestResourcesGet(t *testing.T) {
+	files := `
+-- hugo.toml --
+-- assets/text/txt1.txt --
+Text 1.
+-- assets/text/txt2.txt --
+Text 2.
+-- assets/text/sub/txt3.txt --
+Text 3.
+-- assets/text/sub/txt4.txt --
+Text 4.
+-- content/mybundle/index.md --
+---
+title: "My Bundle"
+---
+-- content/mybundle/txt1.txt --
+Text 1.
+-- content/mybundle/sub/txt2.txt --
+Text 1.
+-- layouts/index.html --
+{{ $mybundle := site.GetPage "mybundle" }}
+{{ $subResources := resources.Match "/text/sub/*.*"  }}
+{{ $subResourcesMount :=  $subResources.Mount "/text/sub" "/newroot" }}
+resources:text/txt1.txt:{{ with resources.Get "text/txt1.txt" }}{{ .Name }}{{ end }}|
+resources:text/txt2.txt:{{ with resources.Get "text/txt2.txt" }}{{ .Name }}{{ end }}|
+resources:text/sub/txt3.txt:{{ with resources.Get "text/sub/txt3.txt" }}{{ .Name }}{{ end }}|
+subResources.range:{{ range $subResources }}{{ .Name }}|{{ end }}|
+subResources:"text/sub/txt3.txt:{{ with $subResources.Get "text/sub/txt3.txt" }}{{ .Name }}{{ end }}|
+subResourcesMount:/newroot/txt3.txt:{{ with $subResourcesMount.Get "/newroot/txt3.txt" }}{{ .Name }}{{ end }}|
+page:txt1.txt:{{ with $mybundle.Resources.Get "txt1.txt" }}{{ .Name }}{{ end }}|
+page:./txt1.txt:{{ with $mybundle.Resources.Get "./txt1.txt" }}{{ .Name }}{{ end }}|
+page:sub/txt2.txt:{{ with $mybundle.Resources.Get "sub/txt2.txt" }}{{ .Name }}{{ end }}|
+`
+	b := hugolib.Test(t, files)
+
+	b.AssertFileContent("public/index.html", `
+resources:text/txt1.txt:/text/txt1.txt|
+resources:text/txt2.txt:/text/txt2.txt|
+resources:text/sub/txt3.txt:/text/sub/txt3.txt|
+subResources:"text/sub/txt3.txt:/text/sub/txt3.txt|
+subResourcesMount:/newroot/txt3.txt:/text/sub/txt3.txt|
+page:txt1.txt:txt1.txt|
+page:./txt1.txt:txt1.txt|
+page:sub/txt2.txt:sub/txt2.txt|
+`)
+}
+
+// TODO1 check .Name in bundles on renames.

internal/js/esbuild/build.go

@@ -0,0 +1,181 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package esbuild provides functions for building JavaScript resources.
+package esbuild
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/evanw/esbuild/pkg/api"
+	"github.com/gohugoio/hugo/common/herrors"
+	"github.com/gohugoio/hugo/common/hugio"
+	"github.com/gohugoio/hugo/common/text"
+	"github.com/gohugoio/hugo/hugofs"
+	"github.com/gohugoio/hugo/hugolib/filesystems"
+	"github.com/gohugoio/hugo/identity"
+	"github.com/gohugoio/hugo/resources"
+)
+
+// NewBuildClient creates a new BuildClient.
+func NewBuildClient(fs *filesystems.SourceFilesystem, rs *resources.Spec) *BuildClient {
+	return &BuildClient{
+		rs:  rs,
+		sfs: fs,
+	}
+}
+
+type BuildClient struct {
+	rs  *resources.Spec
+	sfs *filesystems.SourceFilesystem
+}
+
+func (c *BuildClient) Build(opts Options) (api.BuildResult, error) {
+	dependencyManager := opts.DependencyManager
+	if dependencyManager == nil {
+		dependencyManager = identity.NopManager
+	}
+
+	opts.ResolveDir = c.rs.Cfg.BaseConfig().WorkingDir // where node_modules gets resolved
+	opts.TsConfig = c.rs.ResolveJSConfigFile("tsconfig.json")
+
+	if err := opts.validate(); err != nil {
+		return api.BuildResult{}, err
+	}
+
+	buildOptions, err := toBuildOptions(opts)
+	if err != nil {
+		return api.BuildResult{}, err
+	}
+
+	buildOptions.Plugins, err = createBuildPlugins(c.rs, dependencyManager, opts)
+	if err != nil {
+		return api.BuildResult{}, err
+	}
+
+	if buildOptions.Sourcemap == api.SourceMapExternal && buildOptions.Outdir == "" {
+		buildOptions.Outdir, err = os.MkdirTemp(os.TempDir(), "compileOutput")
+		if err != nil {
+			return api.BuildResult{}, err
+		}
+		defer os.Remove(buildOptions.Outdir)
+	}
+
+	if opts.Inject != nil {
+		// Resolve the absolute filenames.
+		for i, ext := range opts.Inject {
+			impPath := filepath.FromSlash(ext)
+			if filepath.IsAbs(impPath) {
+				return api.BuildResult{}, fmt.Errorf("inject: absolute paths not supported, must be relative to /assets")
+			}
+
+			m := resolveComponentInAssets(c.rs.Assets.Fs, impPath)
+
+			if m == nil {
+				return api.BuildResult{}, fmt.Errorf("inject: file %q not found", ext)
+			}
+
+			opts.Inject[i] = m.Filename
+
+		}
+
+		buildOptions.Inject = opts.Inject
+
+	}
+
+	result := api.Build(buildOptions)
+
+	if len(result.Errors) > 0 {
+		createErr := func(msg api.Message) error {
+			if msg.Location == nil {
+				return errors.New(msg.Text)
+			}
+			var (
+				contentr     hugio.ReadSeekCloser
+				errorMessage string
+				loc          = msg.Location
+				errorPath    = loc.File
+				err          error
+			)
+
+			var resolvedError *ErrorMessageResolved
+
+			if opts.ErrorMessageResolveFunc != nil {
+				resolvedError = opts.ErrorMessageResolveFunc(msg)
+			}
+
+			if resolvedError == nil {
+				if errorPath == stdinImporter {
+					errorPath = "TODO1" // transformCtx.SourcePath
+				}
+
+				errorMessage = msg.Text
+				// TODO1 handle all namespaces, make more general
+				errorMessage = strings.ReplaceAll(errorMessage, NsHugoImport+":", "")
+
+				if strings.HasPrefix(errorPath, NsHugoImport) {
+					errorPath = strings.TrimPrefix(errorPath, NsHugoImport+":")
+					contentr, err = hugofs.Os.Open(errorPath)
+				} else {
+					var fi os.FileInfo
+					fi, err = c.sfs.Fs.Stat(errorPath)
+					if err == nil {
+						m := fi.(hugofs.FileMetaInfo).Meta()
+						errorPath = m.Filename
+						contentr, err = m.Open()
+					}
+				}
+			} else {
+				contentr = resolvedError.Content
+				errorPath = resolvedError.Path
+				errorMessage = resolvedError.Message
+			}
+
+			if contentr != nil {
+				defer contentr.Close()
+			}
+
+			if err == nil {
+				fe := herrors.
+					NewFileErrorFromName(errors.New(errorMessage), errorPath).
+					UpdatePosition(text.Position{Offset: -1, LineNumber: loc.Line, ColumnNumber: loc.Column}).
+					UpdateContent(contentr, nil)
+
+				return fe
+			}
+
+			return fmt.Errorf("%s", errorMessage)
+		}
+
+		var errors []error
+
+		for _, msg := range result.Errors {
+			errors = append(errors, createErr(msg))
+		}
+
+		// Return 1, log the rest.
+		for i, err := range errors {
+			if i > 0 {
+				c.rs.Logger.Errorf("js.Build failed: %s", err)
+			}
+		}
+
+		return result, errors[0]
+	}
+
+	return result, nil
+}

internal/js/esbuild/helpers.go

@@ -0,0 +1,45 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package esbuild provides functions for building JavaScript resources.
+package esbuild
+
+import "github.com/gohugoio/hugo/lazy"
+
+// getOnce is a helper to get a value once.
+// Any invocation after the first one will return T's zero value.
+// This is thread safe.
+// Note that once can be reset.
+type getOnce[T any] struct {
+	v    T
+	once lazy.OnceMore
+}
+
+func (g *getOnce[T]) Get() T {
+	var v T
+	g.once.Do(func() {
+		v = g.v
+	})
+	return v
+}
+
+func (g *getOnce[T]) commit() T {
+	g.once.Do(func() {
+	})
+	return g.v
+}
+
+// TODO1 remove.
+func deb(what string, v ...any) {
+	// fmt.Println(what, v)
+}

internal/js/esbuild/options.go

@@ -0,0 +1,301 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package esbuild
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	"github.com/gohugoio/hugo/common/hugio"
+	"github.com/gohugoio/hugo/common/maps"
+	"github.com/gohugoio/hugo/common/paths"
+	"github.com/gohugoio/hugo/identity"
+
+	"github.com/evanw/esbuild/pkg/api"
+
+	"github.com/gohugoio/hugo/media"
+	"github.com/mitchellh/mapstructure"
+)
+
+type Options struct {
+	ExternalOptions
+	InternalOptions
+}
+
+func (opts *Options) validate() error {
+	if opts.ImportOnResolveFunc != nil && opts.ImportOnLoadFunc == nil {
+		return fmt.Errorf("ImportOnLoadFunc must be set if ImportOnResolveFunc is set")
+	}
+	if opts.ImportOnResolveFunc == nil && opts.ImportOnLoadFunc != nil {
+		return fmt.Errorf("ImportOnResolveFunc must be set if ImportOnLoadFunc is set")
+	}
+	return nil
+}
+
+// InternalOptions holds internal options for the js.Build template function.
+type InternalOptions struct {
+	MediaType  media.Type
+	OutDir     string
+	Contents   string
+	SourceDir  string
+	ResolveDir string
+
+	DependencyManager identity.Manager
+
+	Write                   bool // Set to false to write to memory.
+	AllowOverwrite          bool
+	Splitting               bool
+	TsConfig                string
+	EntryPoints             []string
+	ImportOnResolveFunc     func(identity.Manager, string, api.OnResolveArgs) string
+	ImportOnLoadFunc        func(api.OnLoadArgs) string
+	ImportParamsOnLoadFunc  func(args api.OnLoadArgs) json.RawMessage
+	ErrorMessageResolveFunc func(api.Message) *ErrorMessageResolved
+	Stdin                   bool
+}
+
+type ErrorMessageResolved struct {
+	Path    string
+	Message string
+	Content hugio.ReadSeekCloser
+}
+
+// ExternalOptions holds user facing options for the js.Build template function.
+type ExternalOptions struct {
+	// If not set, the source path will be used as the base target path.
+	// Note that the target path's extension may change if the target MIME type
+	// is different, e.g. when the source is TypeScript.
+	TargetPath string
+
+	// Whether to minify to output.
+	Minify bool
+
+	// Whether to write mapfiles
+	SourceMap string
+
+	// The language target.
+	// One of: es2015, es2016, es2017, es2018, es2019, es2020 or esnext.
+	// Default is esnext.
+	Target string
+
+	// The output format.
+	// One of: iife, cjs, esm
+	// Default is to esm.
+	Format string
+
+	// External dependencies, e.g. "react".
+	Externals []string
+
+	// This option allows you to automatically replace a global variable with an import from another file.
+	// The filenames must be relative to /assets.
+	// See https://esbuild.github.io/api/#inject
+	Inject []string
+
+	// User defined symbols.
+	Defines map[string]any
+
+	// Maps a component import to another.
+	Shims map[string]string
+
+	// User defined params. Will be marshaled to JSON and available as "@params", e.g.
+	//     import * as params from '@params';
+	Params any
+
+	// What to use instead of React.createElement.
+	JSXFactory string
+
+	// What to use instead of React.Fragment.
+	JSXFragment string
+
+	// What to do about JSX syntax.
+	// See https://esbuild.github.io/api/#jsx
+	JSX string
+
+	// Which library to use to automatically import JSX helper functions from. Only works if JSX is set to automatic.
+	// See https://esbuild.github.io/api/#jsx-import-source
+	JSXImportSource string
+
+	// There is/was a bug in WebKit with severe performance issue with the tracking
+	// of TDZ checks in JavaScriptCore.
+	//
+	// Enabling this flag removes the TDZ and `const` assignment checks and
+	// may improve performance of larger JS codebases until the WebKit fix
+	// is in widespread use.
+	//
+	// See https://bugs.webkit.org/show_bug.cgi?id=199866
+	// Deprecated: This no longer have any effect and will be removed.
+	// TODO(bep) remove. See https://github.com/evanw/esbuild/commit/869e8117b499ca1dbfc5b3021938a53ffe934dba
+	AvoidTDZ bool
+}
+
+func DecodeExternalOptions(m map[string]any) (ExternalOptions, error) {
+	var opts ExternalOptions
+
+	if err := mapstructure.WeakDecode(m, &opts); err != nil {
+		return opts, err
+	}
+
+	if opts.TargetPath != "" {
+		opts.TargetPath = paths.ToSlashTrimLeading(opts.TargetPath)
+	}
+
+	opts.Target = strings.ToLower(opts.Target)
+	opts.Format = strings.ToLower(opts.Format)
+
+	return opts, nil
+}
+
+func toBuildOptions(opts Options) (buildOptions api.BuildOptions, err error) {
+	var target api.Target
+	switch opts.Target {
+	case "", "esnext":
+		target = api.ESNext
+	case "es5":
+		target = api.ES5
+	case "es6", "es2015":
+		target = api.ES2015
+	case "es2016":
+		target = api.ES2016
+	case "es2017":
+		target = api.ES2017
+	case "es2018":
+		target = api.ES2018
+	case "es2019":
+		target = api.ES2019
+	case "es2020":
+		target = api.ES2020
+	case "es2021":
+		target = api.ES2021
+	case "es2022":
+		target = api.ES2022
+	case "es2023":
+		target = api.ES2023
+	default:
+		err = fmt.Errorf("invalid target: %q", opts.Target)
+		return
+	}
+
+	mediaType := opts.MediaType
+	if mediaType.IsZero() {
+		mediaType = media.Builtin.JavascriptType
+	}
+
+	var loader api.Loader
+	switch mediaType.SubType {
+	// TODO(bep) ESBuild support a set of other loaders, but I currently fail
+	// to see the relevance. That may change as we start using this.
+	case media.Builtin.JavascriptType.SubType:
+		loader = api.LoaderJS
+	case media.Builtin.TypeScriptType.SubType:
+		loader = api.LoaderTS
+	case media.Builtin.TSXType.SubType:
+		loader = api.LoaderTSX
+	case media.Builtin.JSXType.SubType:
+		loader = api.LoaderJSX
+	default:
+		err = fmt.Errorf("unsupported Media Type: %q", opts.MediaType)
+		return
+	}
+
+	var format api.Format
+	// One of: iife, cjs, esm
+	switch opts.Format {
+	case "", "iife":
+		format = api.FormatIIFE
+	case "esm":
+		format = api.FormatESModule
+	case "cjs":
+		format = api.FormatCommonJS
+	default:
+		err = fmt.Errorf("unsupported script output format: %q", opts.Format)
+		return
+	}
+
+	var jsx api.JSX
+	switch opts.JSX {
+	case "", "transform":
+		jsx = api.JSXTransform
+	case "preserve":
+		jsx = api.JSXPreserve
+	case "automatic":
+		jsx = api.JSXAutomatic
+	default:
+		err = fmt.Errorf("unsupported jsx type: %q", opts.JSX)
+		return
+	}
+
+	var defines map[string]string
+	if opts.Defines != nil {
+		defines = maps.ToStringMapString(opts.Defines)
+	}
+
+	// By default we only need to specify outDir and no outFile
+	outDir := opts.OutDir
+	outFile := ""
+	var sourceMap api.SourceMap
+	switch opts.SourceMap {
+	case "inline":
+		sourceMap = api.SourceMapInline
+	case "external":
+		sourceMap = api.SourceMapExternal
+	case "":
+		sourceMap = api.SourceMapNone
+	default:
+		err = fmt.Errorf("unsupported sourcemap type: %q", opts.SourceMap)
+		return
+	}
+
+	buildOptions = api.BuildOptions{
+		Outfile:  outFile,
+		Bundle:   true,
+		Metafile: true, // TODO1 batch only.
+
+		Target:    target,
+		Format:    format,
+		Sourcemap: sourceMap,
+
+		MinifyWhitespace:  opts.Minify,
+		MinifyIdentifiers: opts.Minify,
+		MinifySyntax:      opts.Minify,
+
+		Outdir:         outDir,
+		Write:          opts.Write,
+		AllowOverwrite: opts.AllowOverwrite,
+		Splitting:      opts.Splitting,
+
+		Define:   defines,
+		External: opts.Externals,
+
+		JSXFactory:  opts.JSXFactory,
+		JSXFragment: opts.JSXFragment,
+
+		JSX:             jsx,
+		JSXImportSource: opts.JSXImportSource,
+
+		Tsconfig: opts.TsConfig,
+
+		EntryPoints: opts.EntryPoints,
+	}
+
+	if opts.Stdin {
+		// This makes ESBuild pass `stdin` as the Importer to the import.
+		buildOptions.Stdin = &api.StdinOptions{
+			Contents:   opts.Contents,
+			ResolveDir: opts.ResolveDir,
+			Loader:     loader,
+		}
+	}
+	return
+}

internal/js/esbuild/options_test.go

@@ -0,0 +1,220 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package esbuild
+
+import (
+	"testing"
+
+	"github.com/gohugoio/hugo/media"
+
+	"github.com/evanw/esbuild/pkg/api"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestToBuildOptions(t *testing.T) {
+	c := qt.New(t)
+
+	opts, err := toBuildOptions(
+		Options{
+			InternalOptions: InternalOptions{
+				MediaType: media.Builtin.JavascriptType,
+				Stdin:     true,
+			},
+		},
+	)
+
+	c.Assert(err, qt.IsNil)
+	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
+		Bundle:   true,
+		Metafile: true,
+		Target:   api.ESNext,
+		Format:   api.FormatIIFE,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+	})
+
+	opts, err = toBuildOptions(
+		Options{
+			ExternalOptions: ExternalOptions{
+				Target:   "es2018",
+				Format:   "cjs",
+				Minify:   true,
+				AvoidTDZ: true,
+			},
+			InternalOptions: InternalOptions{
+				MediaType: media.Builtin.JavascriptType,
+				Stdin:     true,
+			},
+		},
+	)
+	c.Assert(err, qt.IsNil)
+	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
+		Bundle:            true,
+		Metafile:          true,
+		Target:            api.ES2018,
+		Format:            api.FormatCommonJS,
+		MinifyIdentifiers: true,
+		MinifySyntax:      true,
+		MinifyWhitespace:  true,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+	})
+
+	opts, err = toBuildOptions(
+		Options{
+			ExternalOptions: ExternalOptions{
+				Target: "es2018", Format: "cjs", Minify: true,
+				SourceMap: "inline",
+			},
+			InternalOptions: InternalOptions{
+				MediaType: media.Builtin.JavascriptType,
+				Stdin:     true,
+			},
+		},
+	)
+	c.Assert(err, qt.IsNil)
+	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
+		Bundle:            true,
+		Metafile:          true,
+		Target:            api.ES2018,
+		Format:            api.FormatCommonJS,
+		MinifyIdentifiers: true,
+		MinifySyntax:      true,
+		MinifyWhitespace:  true,
+		Sourcemap:         api.SourceMapInline,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+	})
+
+	opts, err = toBuildOptions(
+		Options{
+			ExternalOptions: ExternalOptions{
+				Target: "es2018", Format: "cjs", Minify: true,
+				SourceMap: "inline",
+			},
+			InternalOptions: InternalOptions{
+				MediaType: media.Builtin.JavascriptType,
+				Stdin:     true,
+			},
+		},
+	)
+	c.Assert(err, qt.IsNil)
+	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
+		Bundle:            true,
+		Metafile:          true,
+		Target:            api.ES2018,
+		Format:            api.FormatCommonJS,
+		MinifyIdentifiers: true,
+		MinifySyntax:      true,
+		MinifyWhitespace:  true,
+		Sourcemap:         api.SourceMapInline,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+	})
+
+	opts, err = toBuildOptions(
+		Options{
+			ExternalOptions: ExternalOptions{
+				Target: "es2018", Format: "cjs", Minify: true,
+				SourceMap: "external",
+			},
+			InternalOptions: InternalOptions{
+				MediaType: media.Builtin.JavascriptType,
+				Stdin:     true,
+			},
+		},
+	)
+
+	c.Assert(err, qt.IsNil)
+	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
+		Bundle:            true,
+		Metafile:          true,
+		Target:            api.ES2018,
+		Format:            api.FormatCommonJS,
+		MinifyIdentifiers: true,
+		MinifySyntax:      true,
+		MinifyWhitespace:  true,
+		Sourcemap:         api.SourceMapExternal,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+	})
+
+	opts, err = toBuildOptions(
+		Options{
+			ExternalOptions: ExternalOptions{
+				JSX: "automatic", JSXImportSource: "preact",
+			},
+			InternalOptions: InternalOptions{
+				MediaType: media.Builtin.JavascriptType,
+				Stdin:     true,
+			},
+		},
+	)
+
+	c.Assert(err, qt.IsNil)
+	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
+		Bundle:   true,
+		Metafile: true,
+		Target:   api.ESNext,
+		Format:   api.FormatIIFE,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+		JSX:             api.JSXAutomatic,
+		JSXImportSource: "preact",
+	})
+}
+
+func TestToBuildOptionsTarget(t *testing.T) {
+	c := qt.New(t)
+
+	for _, test := range []struct {
+		target string
+		expect api.Target
+	}{
+		{"es2015", api.ES2015},
+		{"es2016", api.ES2016},
+		{"es2017", api.ES2017},
+		{"es2018", api.ES2018},
+		{"es2019", api.ES2019},
+		{"es2020", api.ES2020},
+		{"es2021", api.ES2021},
+		{"es2022", api.ES2022},
+		{"es2023", api.ES2023},
+		{"", api.ESNext},
+		{"esnext", api.ESNext},
+	} {
+		c.Run(test.target, func(c *qt.C) {
+			opts, err := toBuildOptions(
+				Options{
+					ExternalOptions: ExternalOptions{
+						Target: test.target,
+					},
+					InternalOptions: InternalOptions{
+						MediaType: media.Builtin.JavascriptType,
+					},
+				},
+			)
+
+			c.Assert(err, qt.IsNil)
+			c.Assert(opts.Target, qt.Equals, test.expect)
+		})
+	}
+}

internal/js/esbuild/resolve.go

@@ -0,0 +1,275 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package esbuild
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/evanw/esbuild/pkg/api"
+	"github.com/gohugoio/hugo/hugofs"
+	"github.com/gohugoio/hugo/identity"
+	"github.com/gohugoio/hugo/resources"
+	"github.com/spf13/afero"
+)
+
+const (
+	NsHugoImport            = "ns-hugo-import"
+	NsHugoImportResolveFunc = "ns-hugo-import-resolvefunc"
+	nsHugoParams            = "ns-hugo-params"
+
+	stdinImporter = "<stdin>"
+)
+
+const (
+	PrefixHugoVirtual = "@hugo-virtual"
+)
+
+var extensionToLoaderMap = map[string]api.Loader{
+	".js":   api.LoaderJS,
+	".mjs":  api.LoaderJS,
+	".cjs":  api.LoaderJS,
+	".jsx":  api.LoaderJSX,
+	".ts":   api.LoaderTS,
+	".tsx":  api.LoaderTSX,
+	".css":  api.LoaderCSS,
+	".json": api.LoaderJSON,
+	".txt":  api.LoaderText,
+}
+
+func loaderFromFilename(filename string) api.Loader {
+	l, found := extensionToLoaderMap[filepath.Ext(filename)]
+	if found {
+		return l
+	}
+	return api.LoaderJS
+}
+
+func resolveComponentInAssets(fs afero.Fs, impPath string) *hugofs.FileMeta {
+	findFirst := func(base string) *hugofs.FileMeta {
+		// This is the most common sub-set of ESBuild's default extensions.
+		// We assume that imports of JSON, CSS etc. will be using their full
+		// name with extension.
+		for _, ext := range []string{".js", ".ts", ".tsx", ".jsx"} {
+			if strings.HasSuffix(impPath, ext) {
+				// Import of foo.js.js need the full name.
+				continue
+			}
+			if fi, err := fs.Stat(base + ext); err == nil {
+				return fi.(hugofs.FileMetaInfo).Meta()
+			}
+		}
+
+		// Not found.
+		return nil
+	}
+
+	var m *hugofs.FileMeta
+
+	// We need to check if this is a regular file imported without an extension.
+	// There may be ambiguous situations where both foo.js and foo/index.js exists.
+	// This import order is in line with both how Node and ESBuild's native
+	// import resolver works.
+
+	// It may be a regular file imported without an extension, e.g.
+	// foo or foo/index.
+	m = findFirst(impPath)
+	if m != nil {
+		return m
+	}
+
+	base := filepath.Base(impPath)
+	if base == "index" {
+		// try index.esm.js etc.
+		m = findFirst(impPath + ".esm")
+		if m != nil {
+			return m
+		}
+	}
+
+	// Check the path as is.
+	fi, err := fs.Stat(impPath)
+
+	if err == nil {
+		if fi.IsDir() {
+			m = findFirst(filepath.Join(impPath, "index"))
+			if m == nil {
+				m = findFirst(filepath.Join(impPath, "index.esm"))
+			}
+		} else {
+			m = fi.(hugofs.FileMetaInfo).Meta()
+		}
+	} else if strings.HasSuffix(base, ".js") {
+		m = findFirst(strings.TrimSuffix(impPath, ".js"))
+	}
+
+	return m
+}
+
+func createBuildPlugins(rs *resources.Spec, depsManager identity.Manager, opts Options) ([]api.Plugin, error) {
+	fs := rs.Assets
+
+	resolveImport := func(args api.OnResolveArgs) (api.OnResolveResult, error) {
+		impPath := args.Path
+		shimmed := false
+		if opts.Shims != nil {
+			override, found := opts.Shims[impPath]
+			if found {
+				impPath = override
+				shimmed = true
+			}
+		}
+
+		if opts.ImportOnResolveFunc != nil {
+			if s := opts.ImportOnResolveFunc(depsManager, impPath, args); s != "" {
+				return api.OnResolveResult{Path: s, Namespace: NsHugoImportResolveFunc}, nil
+			}
+		}
+
+		importer := args.Importer
+
+		isStdin := importer == stdinImporter
+		var relDir string
+		if !isStdin {
+			if strings.HasPrefix(importer, PrefixHugoVirtual) {
+				relDir = filepath.Dir(strings.TrimPrefix(importer, PrefixHugoVirtual))
+			} else {
+				rel, found := fs.MakePathRelative(importer, true)
+
+				if !found {
+					if shimmed {
+						relDir = opts.SourceDir
+					} else {
+						// Not in any of the /assets folders.
+						// This is an import from a node_modules, let
+						// ESBuild resolve this.
+						return api.OnResolveResult{}, nil
+					}
+				} else {
+					relDir = filepath.Dir(rel)
+				}
+			}
+		} else {
+			relDir = opts.SourceDir
+		}
+
+		// Imports not starting with a "." is assumed to live relative to /assets.
+		// Hugo makes no assumptions about the directory structure below /assets.
+		if relDir != "" && strings.HasPrefix(impPath, ".") {
+			impPath = filepath.Join(relDir, impPath)
+		}
+
+		m := resolveComponentInAssets(fs.Fs, impPath)
+
+		if m != nil {
+			depsManager.AddIdentity(m.PathInfo)
+
+			// Store the source root so we can create a jsconfig.json
+			// to help IntelliSense when the build is done.
+			// This should be a small number of elements, and when
+			// in server mode, we may get stale entries on renames etc.,
+			// but that shouldn't matter too much.
+			rs.JSConfigBuilder.AddSourceRoot(m.SourceRoot)
+			return api.OnResolveResult{Path: m.Filename, Namespace: NsHugoImport}, nil
+		}
+
+		// Fall back to ESBuild's resolve.
+		return api.OnResolveResult{}, nil
+	}
+
+	importResolver := api.Plugin{
+		Name: "hugo-import-resolver",
+		Setup: func(build api.PluginBuild) {
+			build.OnResolve(api.OnResolveOptions{Filter: `.*`},
+				func(args api.OnResolveArgs) (api.OnResolveResult, error) {
+					return resolveImport(args)
+				})
+			build.OnLoad(api.OnLoadOptions{Filter: `.*`, Namespace: NsHugoImport},
+				func(args api.OnLoadArgs) (api.OnLoadResult, error) {
+					b, err := os.ReadFile(args.Path)
+					if err != nil {
+						return api.OnLoadResult{}, fmt.Errorf("failed to read %q: %w", args.Path, err)
+					}
+					c := string(b)
+
+					return api.OnLoadResult{
+						// See https://github.com/evanw/esbuild/issues/502
+						// This allows all modules to resolve dependencies
+						// in the main project's node_modules.
+						ResolveDir: opts.ResolveDir,
+						Contents:   &c,
+						Loader:     loaderFromFilename(args.Path),
+					}, nil
+				})
+			build.OnLoad(api.OnLoadOptions{Filter: `.*`, Namespace: NsHugoImportResolveFunc},
+				func(args api.OnLoadArgs) (api.OnLoadResult, error) {
+					c := opts.ImportOnLoadFunc(args)
+					if c == "" {
+						return api.OnLoadResult{}, fmt.Errorf("ImportOnLoadFunc failed to resolve %q", args.Path)
+					}
+
+					return api.OnLoadResult{
+						ResolveDir: opts.ResolveDir,
+						Contents:   &c,
+						Loader:     loaderFromFilename(args.Path),
+					}, nil
+				})
+		},
+	}
+
+	params := opts.Params
+	if params == nil {
+		// This way @params will always resolve to something.
+		params = make(map[string]any)
+	}
+
+	b, err := json.Marshal(params)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal params: %w", err)
+	}
+	paramsPlugin := api.Plugin{
+		Name: "hugo-params-plugin",
+		Setup: func(build api.PluginBuild) {
+			build.OnResolve(api.OnResolveOptions{Filter: `^@params$`},
+				func(args api.OnResolveArgs) (api.OnResolveResult, error) {
+					return api.OnResolveResult{
+						Path:      args.Importer,
+						Namespace: nsHugoParams,
+					}, nil
+				})
+			build.OnLoad(api.OnLoadOptions{Filter: `.*`, Namespace: nsHugoParams},
+				func(args api.OnLoadArgs) (api.OnLoadResult, error) {
+					bb := b
+
+					if opts.ImportParamsOnLoadFunc != nil {
+						if bbb := opts.ImportParamsOnLoadFunc(args); bbb != nil {
+							bb = bbb
+						}
+					}
+
+					s := string(bb)
+
+					return api.OnLoadResult{
+						Contents: &s,
+						Loader:   api.LoaderJSON,
+					}, nil
+				})
+		},
+	}
+
+	return []api.Plugin{importResolver, paramsPlugin}, nil
+}

internal/js/esbuild/resolve_test.go

@@ -0,0 +1,85 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package esbuild
+
+import (
+	"path"
+	"path/filepath"
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+	"github.com/gohugoio/hugo/config"
+	"github.com/gohugoio/hugo/config/testconfig"
+	"github.com/gohugoio/hugo/hugofs"
+	"github.com/gohugoio/hugo/hugolib/filesystems"
+	"github.com/gohugoio/hugo/hugolib/paths"
+	"github.com/spf13/afero"
+)
+
+func TestResolveComponentInAssets(t *testing.T) {
+	c := qt.New(t)
+
+	for _, test := range []struct {
+		name    string
+		files   []string
+		impPath string
+		expect  string
+	}{
+		{"Basic, extension", []string{"foo.js", "bar.js"}, "foo.js", "foo.js"},
+		{"Basic, no extension", []string{"foo.js", "bar.js"}, "foo", "foo.js"},
+		{"Basic, no extension, typescript", []string{"foo.ts", "bar.js"}, "foo", "foo.ts"},
+		{"Not found", []string{"foo.js", "bar.js"}, "moo.js", ""},
+		{"Not found, double js extension", []string{"foo.js.js", "bar.js"}, "foo.js", ""},
+		{"Index file, folder only", []string{"foo/index.js", "bar.js"}, "foo", "foo/index.js"},
+		{"Index file, folder and index", []string{"foo/index.js", "bar.js"}, "foo/index", "foo/index.js"},
+		{"Index file, folder and index and suffix", []string{"foo/index.js", "bar.js"}, "foo/index.js", "foo/index.js"},
+		{"Index ESM file, folder only", []string{"foo/index.esm.js", "bar.js"}, "foo", "foo/index.esm.js"},
+		{"Index ESM file, folder and index", []string{"foo/index.esm.js", "bar.js"}, "foo/index", "foo/index.esm.js"},
+		{"Index ESM file, folder and index and suffix", []string{"foo/index.esm.js", "bar.js"}, "foo/index.esm.js", "foo/index.esm.js"},
+		// We added these index.esm.js cases in v0.101.0. The case below is unlikely to happen in the wild, but add a test
+		// to document Hugo's behavior. We pick the file with the name index.js; anything else would be breaking.
+		{"Index and Index ESM file, folder only", []string{"foo/index.esm.js", "foo/index.js", "bar.js"}, "foo", "foo/index.js"},
+
+		// Issue #8949
+		{"Check file before directory", []string{"foo.js", "foo/index.js"}, "foo", "foo.js"},
+	} {
+		c.Run(test.name, func(c *qt.C) {
+			baseDir := "assets"
+			mfs := afero.NewMemMapFs()
+
+			for _, filename := range test.files {
+				c.Assert(afero.WriteFile(mfs, filepath.Join(baseDir, filename), []byte("let foo='bar';"), 0o777), qt.IsNil)
+			}
+
+			conf := testconfig.GetTestConfig(mfs, config.New())
+			fs := hugofs.NewFrom(mfs, conf.BaseConfig())
+
+			p, err := paths.New(fs, conf)
+			c.Assert(err, qt.IsNil)
+			bfs, err := filesystems.NewBase(p, nil)
+			c.Assert(err, qt.IsNil)
+
+			got := resolveComponentInAssets(bfs.Assets.Fs, test.impPath)
+
+			gotPath := ""
+			expect := test.expect
+			if got != nil {
+				gotPath = filepath.ToSlash(got.Filename)
+				expect = path.Join(baseDir, test.expect)
+			}
+
+			c.Assert(gotPath, qt.Equals, expect)
+		})
+	}
+}

media/mediaType.go

@@ -273,9 +273,13 @@ func (t Types) GetByType(tp string) (Type, bool) {
 	return Type{}, false
 }
 
+func (t Types) normalizeSuffix(s string) string {
+	return strings.ToLower(strings.TrimPrefix(s, "."))
+}
+
 // BySuffix will return all media types matching a suffix.
 func (t Types) BySuffix(suffix string) []Type {
-	suffix = strings.ToLower(suffix)
+	suffix = t.normalizeSuffix(suffix)
 	var types []Type
 	for _, tt := range t {
 		if tt.hasSuffix(suffix) {
@@ -287,7 +291,7 @@ func (t Types) BySuffix(suffix string) []Type {
 
 // GetFirstBySuffix will return the first type matching the given suffix.
 func (t Types) GetFirstBySuffix(suffix string) (Type, SuffixInfo, bool) {
-	suffix = strings.ToLower(suffix)
+	suffix = t.normalizeSuffix(suffix)
 	for _, tt := range t {
 		if tt.hasSuffix(suffix) {
 			return tt, SuffixInfo{
@@ -304,7 +308,7 @@ func (t Types) GetFirstBySuffix(suffix string) (Type, SuffixInfo, bool) {
 // is ambiguous.
 // The lookup is case insensitive.
 func (t Types) GetBySuffix(suffix string) (tp Type, si SuffixInfo, found bool) {
-	suffix = strings.ToLower(suffix)
+	suffix = t.normalizeSuffix(suffix)
 	for _, tt := range t {
 		if tt.hasSuffix(suffix) {
 			if found {
@@ -324,7 +328,7 @@ func (t Types) GetBySuffix(suffix string) (tp Type, si SuffixInfo, found bool) {
 }
 
 func (t Types) IsTextSuffix(suffix string) bool {
-	suffix = strings.ToLower(suffix)
+	suffix = t.normalizeSuffix(suffix)
 	for _, tt := range t {
 		if tt.hasSuffix(suffix) {
 			return tt.IsText()

output/outputFormat.go

@@ -120,6 +120,14 @@ var (
 		Rel:         "alternate",
 	}
 
+	GoTmplFormat = Format{
+		Name:           "gotmpl",
+		MediaType:      media.Builtin.TextType,
+		BaseName:       "index",
+		IsPlainText:    true,
+		NotAlternative: true,
+	}
+
 	HTMLFormat = Format{
 		Name:          "html",
 		MediaType:     media.Builtin.HTMLType,
@@ -215,6 +223,7 @@ var DefaultFormats = Formats{
 	RobotsTxtFormat,
 	RSSFormat,
 	SitemapFormat,
+	GoTmplFormat,
 }
 
 func init() {

resources/page/page.go

@@ -71,8 +71,7 @@ type ChildCareProvider interface {
 	// section.
 	RegularPagesRecursive() Pages
 
-	// Resources returns a list of all resources.
-	Resources() resource.Resources
+	resource.ResourcesProvider
 }
 
 type MarkupProvider interface {

resources/resource.go

@@ -47,6 +47,7 @@ var (
 	_ resource.Cloner                    = (*genericResource)(nil)
 	_ resource.ResourcesLanguageMerger   = (*resource.Resources)(nil)
 	_ resource.Identifier                = (*genericResource)(nil)
+	_ resource.PathProvider              = (*genericResource)(nil)
 	_ identity.IdentityGroupProvider     = (*genericResource)(nil)
 	_ identity.DependencyManagerProvider = (*genericResource)(nil)
 	_ identity.Identity                  = (*genericResource)(nil)
@@ -463,6 +464,11 @@ func (l *genericResource) Key() string {
 	return key
 }
 
+// TODO1 test and document this. Consider adding it to the Resource interface.
+func (l *genericResource) Path() string {
+	return l.paths.TargetPath()
+}
+
 func (l *genericResource) MediaType() media.Type {
 	return l.sd.MediaType
 }

resources/resource/resources.go

@@ -16,8 +16,10 @@ package resource
 
 import (
 	"fmt"
+	"path"
 	"strings"
 
+	"github.com/gohugoio/hugo/common/maps"
 	"github.com/gohugoio/hugo/common/paths"
 	"github.com/gohugoio/hugo/hugofs/glob"
 	"github.com/spf13/cast"
@@ -29,6 +31,53 @@ var _ ResourceFinder = (*Resources)(nil)
 // I.e. both pages and images etc.
 type Resources []Resource
 
+// TODO1
+// TODO1 move to a func + template func. Maybe.
+func (r Resources) Mount(base, target string) ResourceGetter {
+	return resourceGetterFunc(func(namev any) Resource {
+		name1, err := cast.ToStringE(namev)
+		if err != nil {
+			panic(err)
+		}
+
+		isTargetAbs := strings.HasPrefix(target, "/")
+
+		if target != "" {
+			name1 = strings.TrimPrefix(name1, target)
+			if !isTargetAbs {
+				name1 = paths.TrimLeading(name1)
+			}
+		}
+
+		if base != "" && isTargetAbs {
+			name1 = path.Join(base, name1)
+		}
+
+		for _, res := range r {
+			name2 := res.Name()
+
+			if base != "" && !isTargetAbs {
+				name2 = paths.TrimLeading(strings.TrimPrefix(name2, base))
+			}
+
+			// TODO1 remove.
+			// fmt.Println("name1", name1, "name2", name2, "base", base)
+
+			if strings.EqualFold(name1, name2) {
+				return res
+			}
+
+		}
+
+		return nil
+	})
+}
+
+type ResourcesProvider interface {
+	// Resources returns a list of all resources.
+	Resources() Resources
+}
+
 // var _ resource.ResourceFinder = (*Namespace)(nil)
 // ResourcesConverter converts a given slice of Resource objects to Resources.
 type ResourcesConverter interface {
@@ -63,13 +112,25 @@ func (r Resources) Get(name any) Resource {
 		panic(err)
 	}
 
-	namestr = paths.AddLeadingSlash(namestr)
+	isDotCurrent := strings.HasPrefix(namestr, "./")
+	if isDotCurrent {
+		namestr = strings.TrimPrefix(namestr, "./")
+	} else {
+		namestr = paths.AddLeadingSlash(namestr)
+	}
+
+	check := func(name string) bool {
+		if !isDotCurrent {
+			name = paths.AddLeadingSlash(name)
+		}
+		return strings.EqualFold(namestr, name)
+	}
 
 	// First check the Name.
 	// Note that this can be modified by the user in the front matter,
 	// also, it does not contain any language code.
 	for _, resource := range r {
-		if strings.EqualFold(namestr, paths.AddLeadingSlash(resource.Name())) {
+		if check(resource.Name()) {
 			return resource
 		}
 	}
@@ -77,7 +138,7 @@ func (r Resources) Get(name any) Resource {
 	// Finally, check the normalized name.
 	for _, resource := range r {
 		if nop, ok := resource.(NameNormalizedProvider); ok {
-			if strings.EqualFold(namestr, paths.AddLeadingSlash(nop.NameNormalized())) {
+			if check(nop.NameNormalized()) {
 				return resource
 			}
 		}
@@ -197,14 +258,35 @@ type Source interface {
 	Publish() error
 }
 
-// ResourceFinder provides methods to find Resources.
-// Note that GetRemote (as found in resources.GetRemote) is
-// not covered by this interface, as this is only available as a global template function.
-type ResourceFinder interface {
+type ResourceGetter interface {
 	// Get locates the Resource with the given name in the current context (e.g. in .Page.Resources).
 	//
 	// It returns nil if no Resource could found, panics if name is invalid.
 	Get(name any) Resource
+}
+
+type IsProbablySameResourceGetter interface {
+	IsProbablySameResourceGetter(other ResourceGetter) bool
+}
+
+// StaleInfoResourceGetter is a ResourceGetter that also provides information about
+// whether the underlying resources are stale.
+type StaleInfoResourceGetter interface {
+	StaleInfo
+	ResourceGetter
+}
+
+type resourceGetterFunc func(name any) Resource
+
+func (f resourceGetterFunc) Get(name any) Resource {
+	return f(name)
+}
+
+// ResourceFinder provides methods to find Resources.
+// Note that GetRemote (as found in resources.GetRemote) is
+// not covered by this interface, as this is only available as a global template function.
+type ResourceFinder interface {
+	ResourceGetter
 
 	// GetMatch finds the first Resource matching the given pattern, or nil if none found.
 	//
@@ -235,3 +317,92 @@ type ResourceFinder interface {
 	// It returns nil if no Resources could found, panics if typ is invalid.
 	ByType(typ any) Resources
 }
+
+// NewCachedResourceGetter creates a new ResourceGetter from the given objects.
+// If multiple objects are provided, they are merged into one where
+// the first match wins.
+func NewCachedResourceGetter(os ...any) *cachedResourceGetter {
+	var getters multiResourceGetter
+	for _, o := range os {
+		if g, ok := unwrapResourceGetter(o); ok {
+			getters = append(getters, g)
+		}
+	}
+
+	return &cachedResourceGetter{
+		cache:    maps.NewCache[string, Resource](),
+		delegate: getters,
+	}
+}
+
+type multiResourceGetter []ResourceGetter
+
+func (m multiResourceGetter) Get(name any) Resource {
+	for _, g := range m {
+		if res := g.Get(name); res != nil {
+			return res
+		}
+	}
+	return nil
+}
+
+var (
+	_ ResourceGetter               = (*cachedResourceGetter)(nil)
+	_ IsProbablySameResourceGetter = (*cachedResourceGetter)(nil)
+)
+
+type cachedResourceGetter struct {
+	cache    *maps.Cache[string, Resource]
+	delegate ResourceGetter
+}
+
+func (c *cachedResourceGetter) Get(name any) Resource {
+	namestr, err := cast.ToStringE(name)
+	if err != nil {
+		panic(err)
+	}
+	v, _ := c.cache.GetOrCreate(namestr, func() (Resource, error) {
+		v := c.delegate.Get(name)
+		return v, nil
+	})
+	return v
+}
+
+func (c *cachedResourceGetter) IsProbablySameResourceGetter(other ResourceGetter) bool {
+	isProbablyEq := true
+	var count int
+	c.cache.ForEeach(func(k string, v Resource) bool {
+		count++
+		if v != other.Get(k) {
+			isProbablyEq = false
+			return false
+		}
+		return true
+	})
+
+	return count > 0 && isProbablyEq
+}
+
+func unwrapResourceGetter(v any) (ResourceGetter, bool) {
+	if v == nil {
+		return nil, false
+	}
+	switch vv := v.(type) {
+	case ResourceGetter:
+		return vv, true
+	case ResourcesProvider:
+		return vv.Resources(), true
+	case func(name any) Resource:
+		return resourceGetterFunc(vv), true
+	case []any:
+		var getters multiResourceGetter
+		for _, vv := range vv {
+			if g, ok := unwrapResourceGetter(vv); ok {
+				getters = append(getters, g)
+			}
+		}
+		return getters, len(getters) > 0
+	}
+
+	return nil, false
+}

resources/resource/resources_test.go

@@ -0,0 +1,125 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package resource
+
+import (
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestResourcesMount(t *testing.T) {
+	c := qt.New(t)
+	c.Assert(true, qt.IsTrue)
+
+	var m ResourceGetter
+	var r Resources
+
+	check := func(in, expect string) {
+		c.Helper()
+		r := m.Get(in)
+		c.Assert(r, qt.Not(qt.IsNil))
+		c.Assert(r.Name(), qt.Equals, expect)
+	}
+
+	checkNil := func(in string) {
+		c.Helper()
+		r := m.Get(in)
+		c.Assert(r, qt.IsNil)
+	}
+
+	// Misc tests.
+	r = Resources{
+		testResource{name: "/foo/theme.css"},
+	}
+
+	m = r.Mount("/foo", ".")
+	check("./theme.css", "/foo/theme.css")
+
+	// Relative target.
+	r = Resources{
+		testResource{name: "/a/b/c/d.txt"},
+		testResource{name: "/a/b/c/e/f.txt"},
+		testResource{name: "/a/b/d.txt"},
+		testResource{name: "/a/b/e.txt"},
+	}
+
+	// namvev ./theme.css base /js/hugoheadlessui/components target . name /js/hugoheadlessui/components/theme.css name1 theme.css name2 .
+
+	m = r.Mount("/a/b/c", "z")
+	check("z/d.txt", "/a/b/c/d.txt")
+	// check("./z/d.txt", "/a/b/c/d.txt")
+	check("z/e/f.txt", "/a/b/c/e/f.txt")
+
+	m = r.Mount("/a/b", "")
+	check("d.txt", "/a/b/d.txt")
+	m = r.Mount("/a/b", ".")
+	check("d.txt", "/a/b/d.txt")
+	m = r.Mount("/a/b", "./")
+	check("d.txt", "/a/b/d.txt")
+	check("./d.txt", "/a/b/d.txt")
+
+	m = r.Mount("/a/b", ".")
+	check("./d.txt", "/a/b/d.txt")
+
+	// Absolute target.
+	m = r.Mount("/a/b/c", "/z")
+	check("/z/d.txt", "/a/b/c/d.txt")
+	check("/z/e/f.txt", "/a/b/c/e/f.txt")
+	checkNil("/z/f.txt")
+
+	m = r.Mount("/a/b", "/z")
+	check("/z/c/d.txt", "/a/b/c/d.txt")
+	check("/z/c/e/f.txt", "/a/b/c/e/f.txt")
+	check("/z/d.txt", "/a/b/d.txt")
+	checkNil("/z/f.txt")
+
+	m = r.Mount("", "")
+	check("/a/b/c/d.txt", "/a/b/c/d.txt")
+	check("/a/b/c/e/f.txt", "/a/b/c/e/f.txt")
+	check("/a/b/d.txt", "/a/b/d.txt")
+	checkNil("/a/b/f.txt")
+
+	m = r.Mount("/a/b", "/a/b")
+	check("/a/b/c/d.txt", "/a/b/c/d.txt")
+	check("/a/b/c/e/f.txt", "/a/b/c/e/f.txt")
+	check("/a/b/d.txt", "/a/b/d.txt")
+	checkNil("/a/b/f.txt")
+
+	// Resources with relative paths.
+	r = Resources{
+		testResource{name: "a/b/c/d.txt"},
+		testResource{name: "a/b/c/e/f.txt"},
+		testResource{name: "a/b/d.txt"},
+		testResource{name: "a/b/e.txt"},
+		testResource{name: "n.txt"},
+	}
+
+	m = r.Mount("a/b", "z")
+	check("z/d.txt", "a/b/d.txt")
+	checkNil("/z/d.txt")
+}
+
+type testResource struct {
+	Resource
+	name string
+}
+
+func (r testResource) Name() string {
+	return r.name
+}
+
+func (r testResource) NameNormalized() string {
+	return r.name
+}

resources/resource/resourcetypes.go

@@ -108,6 +108,14 @@ type MediaTypeProvider interface {
 	MediaType() media.Type
 }
 
+// TODO1 consider removing.s
+type PathProvider interface {
+	// Path is the relative path to this resource.
+	// In most cases this will be the same as the RelPermalink(),
+	// but it will not trigger any lazy publishing.
+	Path() string
+}
+
 type ResourceLinksProvider interface {
 	// Permalink represents the absolute link to this resource.
 	Permalink() string
@@ -244,6 +252,13 @@ type StaleInfo interface {
 	StaleVersion() uint32
 }
 
+// StaleInfoFunc is a function that returns the StaleVersion for one or more resources.
+type StaleInfoFunc func() uint32
+
+func (f StaleInfoFunc) StaleVersion() uint32 {
+	return f()
+}
+
 // StaleVersion returns the StaleVersion for the given os,
 // or 0 if not set.
 func StaleVersion(os any) uint32 {

resources/resource_transformers/js/build.go

@@ -1,4 +1,4 @@
-// Copyright 2020 The Hugo Authors. All rights reserved.
+// Copyright 2024 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -14,209 +14,64 @@
 package js
 
 import (
-	"errors"
-	"fmt"
-	"io"
-	"os"
 	"path"
-	"path/filepath"
 	"regexp"
-	"strings"
-
-	"github.com/spf13/afero"
-
-	"github.com/gohugoio/hugo/hugofs"
-	"github.com/gohugoio/hugo/media"
-
-	"github.com/gohugoio/hugo/common/herrors"
-	"github.com/gohugoio/hugo/common/text"
-
-	"github.com/gohugoio/hugo/hugolib/filesystems"
-	"github.com/gohugoio/hugo/resources/internal"
 
 	"github.com/evanw/esbuild/pkg/api"
+	"github.com/gohugoio/hugo/hugolib/filesystems"
+	"github.com/gohugoio/hugo/internal/js/esbuild"
+
 	"github.com/gohugoio/hugo/resources"
 	"github.com/gohugoio/hugo/resources/resource"
 )
 
 // Client context for ESBuild.
 type Client struct {
-	rs  *resources.Spec
-	sfs *filesystems.SourceFilesystem
+	c *esbuild.BuildClient
 }
 
 // New creates a new client context.
 func New(fs *filesystems.SourceFilesystem, rs *resources.Spec) *Client {
 	return &Client{
-		rs:  rs,
-		sfs: fs,
+		c: esbuild.NewBuildClient(fs, rs),
 	}
 }
 
-type buildTransformation struct {
-	optsm map[string]any
-	c     *Client
-}
-
-func (t *buildTransformation) Key() internal.ResourceTransformationKey {
-	return internal.NewResourceTransformationKey("jsbuild", t.optsm)
-}
-
-func (t *buildTransformation) Transform(ctx *resources.ResourceTransformationCtx) error {
-	ctx.OutMediaType = media.Builtin.JavascriptType
-
-	opts, err := decodeOptions(t.optsm)
-	if err != nil {
-		return err
-	}
-
-	if opts.TargetPath != "" {
-		ctx.OutPath = opts.TargetPath
-	} else {
-		ctx.ReplaceOutPathExtension(".js")
-	}
-
-	src, err := io.ReadAll(ctx.From)
-	if err != nil {
-		return err
-	}
-
-	opts.sourceDir = filepath.FromSlash(path.Dir(ctx.SourcePath))
-	opts.resolveDir = t.c.rs.Cfg.BaseConfig().WorkingDir // where node_modules gets resolved
-	opts.contents = string(src)
-	opts.mediaType = ctx.InMediaType
-	opts.tsConfig = t.c.rs.ResolveJSConfigFile("tsconfig.json")
-
-	buildOptions, err := toBuildOptions(opts)
-	if err != nil {
-		return err
-	}
-
-	buildOptions.Plugins, err = createBuildPlugins(ctx.DependencyManager, t.c, opts)
-	if err != nil {
-		return err
-	}
-
-	if buildOptions.Sourcemap == api.SourceMapExternal && buildOptions.Outdir == "" {
-		buildOptions.Outdir, err = os.MkdirTemp(os.TempDir(), "compileOutput")
-		if err != nil {
-			return err
-		}
-		defer os.Remove(buildOptions.Outdir)
-	}
-
-	if opts.Inject != nil {
-		// Resolve the absolute filenames.
-		for i, ext := range opts.Inject {
-			impPath := filepath.FromSlash(ext)
-			if filepath.IsAbs(impPath) {
-				return fmt.Errorf("inject: absolute paths not supported, must be relative to /assets")
-			}
-
-			m := resolveComponentInAssets(t.c.rs.Assets.Fs, impPath)
-
-			if m == nil {
-				return fmt.Errorf("inject: file %q not found", ext)
-			}
-
-			opts.Inject[i] = m.Filename
-
-		}
-
-		buildOptions.Inject = opts.Inject
-
-	}
-
-	result := api.Build(buildOptions)
-
-	if len(result.Errors) > 0 {
-
-		createErr := func(msg api.Message) error {
-			loc := msg.Location
-			if loc == nil {
-				return errors.New(msg.Text)
-			}
-			path := loc.File
-			if path == stdinImporter {
-				path = ctx.SourcePath
-			}
-
-			errorMessage := msg.Text
-			errorMessage = strings.ReplaceAll(errorMessage, nsImportHugo+":", "")
-
-			var (
-				f   afero.File
-				err error
-			)
-
-			if strings.HasPrefix(path, nsImportHugo) {
-				path = strings.TrimPrefix(path, nsImportHugo+":")
-				f, err = hugofs.Os.Open(path)
-			} else {
-				var fi os.FileInfo
-				fi, err = t.c.sfs.Fs.Stat(path)
-				if err == nil {
-					m := fi.(hugofs.FileMetaInfo).Meta()
-					path = m.Filename
-					f, err = m.Open()
-				}
-
-			}
-
-			if err == nil {
-				fe := herrors.
-					NewFileErrorFromName(errors.New(errorMessage), path).
-					UpdatePosition(text.Position{Offset: -1, LineNumber: loc.Line, ColumnNumber: loc.Column}).
-					UpdateContent(f, nil)
-
-				f.Close()
-				return fe
-			}
-
-			return fmt.Errorf("%s", errorMessage)
-		}
-
-		var errors []error
-
-		for _, msg := range result.Errors {
-			errors = append(errors, createErr(msg))
-		}
-
-		// Return 1, log the rest.
-		for i, err := range errors {
-			if i > 0 {
-				t.c.rs.Logger.Errorf("js.Build failed: %s", err)
-			}
-		}
-
-		return errors[0]
-	}
-
-	if buildOptions.Sourcemap == api.SourceMapExternal {
-		content := string(result.OutputFiles[1].Contents)
-		symPath := path.Base(ctx.OutPath) + ".map"
-		re := regexp.MustCompile(`//# sourceMappingURL=.*\n?`)
-		content = re.ReplaceAllString(content, "//# sourceMappingURL="+symPath+"\n")
-
-		if err = ctx.PublishSourceMap(string(result.OutputFiles[0].Contents)); err != nil {
-			return err
-		}
-		_, err := ctx.To.Write([]byte(content))
-		if err != nil {
-			return err
-		}
-	} else {
-		_, err := ctx.To.Write(result.OutputFiles[0].Contents)
-		if err != nil {
-			return err
-		}
-	}
-	return nil
-}
-
-// Process process esbuild transform
+// Process processes a resource with the user provided options.
 func (c *Client) Process(res resources.ResourceTransformer, opts map[string]any) (resource.Resource, error) {
 	return res.Transform(
 		&buildTransformation{c: c, optsm: opts},
 	)
 }
+
+func (c *Client) transform(opts esbuild.Options, transformCtx *resources.ResourceTransformationCtx) (api.BuildResult, error) {
+	if transformCtx.DependencyManager != nil {
+		opts.DependencyManager = transformCtx.DependencyManager
+	}
+	result, err := c.c.Build(opts)
+	if err != nil {
+		return result, err
+	}
+
+	if opts.ExternalOptions.SourceMap == "external" {
+		content := string(result.OutputFiles[1].Contents)
+		symPath := path.Base(transformCtx.OutPath) + ".map"
+		re := regexp.MustCompile(`//# sourceMappingURL=.*\n?`)
+		content = re.ReplaceAllString(content, "//# sourceMappingURL="+symPath+"\n")
+
+		if err = transformCtx.PublishSourceMap(string(result.OutputFiles[0].Contents)); err != nil {
+			return result, err
+		}
+		_, err := transformCtx.To.Write([]byte(content))
+		if err != nil {
+			return result, err
+		}
+	} else {
+		_, err := transformCtx.To.Write(result.OutputFiles[0].Contents)
+		if err != nil {
+			return result, err
+		}
+
+	}
+	return result, nil
+}

resources/resource_transformers/js/build_test.go

@@ -1,14 +0,0 @@
-// Copyright 2020 The Hugo Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package js

resources/resource_transformers/js/js_integration_test.go

@@ -1,4 +1,4 @@
-// Copyright 2021 The Hugo Authors. All rights reserved.
+// Copyright 2024 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.

resources/resource_transformers/js/options.go

@@ -1,461 +0,0 @@
-// Copyright 2020 The Hugo Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package js
-
-import (
-	"encoding/json"
-	"fmt"
-	"os"
-	"path/filepath"
-	"strings"
-
-	"github.com/gohugoio/hugo/common/maps"
-	"github.com/gohugoio/hugo/common/paths"
-	"github.com/gohugoio/hugo/identity"
-	"github.com/spf13/afero"
-
-	"github.com/evanw/esbuild/pkg/api"
-
-	"github.com/gohugoio/hugo/hugofs"
-	"github.com/gohugoio/hugo/media"
-	"github.com/mitchellh/mapstructure"
-)
-
-const (
-	nsImportHugo = "ns-hugo"
-	nsParams     = "ns-params"
-
-	stdinImporter = "<stdin>"
-)
-
-// Options esbuild configuration
-type Options struct {
-	// If not set, the source path will be used as the base target path.
-	// Note that the target path's extension may change if the target MIME type
-	// is different, e.g. when the source is TypeScript.
-	TargetPath string
-
-	// Whether to minify to output.
-	Minify bool
-
-	// Whether to write mapfiles
-	SourceMap string
-
-	// The language target.
-	// One of: es2015, es2016, es2017, es2018, es2019, es2020 or esnext.
-	// Default is esnext.
-	Target string
-
-	// The output format.
-	// One of: iife, cjs, esm
-	// Default is to esm.
-	Format string
-
-	// External dependencies, e.g. "react".
-	Externals []string
-
-	// This option allows you to automatically replace a global variable with an import from another file.
-	// The filenames must be relative to /assets.
-	// See https://esbuild.github.io/api/#inject
-	Inject []string
-
-	// User defined symbols.
-	Defines map[string]any
-
-	// Maps a component import to another.
-	Shims map[string]string
-
-	// User defined params. Will be marshaled to JSON and available as "@params", e.g.
-	//     import * as params from '@params';
-	Params any
-
-	// What to use instead of React.createElement.
-	JSXFactory string
-
-	// What to use instead of React.Fragment.
-	JSXFragment string
-
-	// What to do about JSX syntax.
-	// See https://esbuild.github.io/api/#jsx
-	JSX string
-
-	// Which library to use to automatically import JSX helper functions from. Only works if JSX is set to automatic.
-	// See https://esbuild.github.io/api/#jsx-import-source
-	JSXImportSource string
-
-	// There is/was a bug in WebKit with severe performance issue with the tracking
-	// of TDZ checks in JavaScriptCore.
-	//
-	// Enabling this flag removes the TDZ and `const` assignment checks and
-	// may improve performance of larger JS codebases until the WebKit fix
-	// is in widespread use.
-	//
-	// See https://bugs.webkit.org/show_bug.cgi?id=199866
-	// Deprecated: This no longer have any effect and will be removed.
-	// TODO(bep) remove. See https://github.com/evanw/esbuild/commit/869e8117b499ca1dbfc5b3021938a53ffe934dba
-	AvoidTDZ bool
-
-	mediaType  media.Type
-	outDir     string
-	contents   string
-	sourceDir  string
-	resolveDir string
-	tsConfig   string
-}
-
-func decodeOptions(m map[string]any) (Options, error) {
-	var opts Options
-
-	if err := mapstructure.WeakDecode(m, &opts); err != nil {
-		return opts, err
-	}
-
-	if opts.TargetPath != "" {
-		opts.TargetPath = paths.ToSlashTrimLeading(opts.TargetPath)
-	}
-
-	opts.Target = strings.ToLower(opts.Target)
-	opts.Format = strings.ToLower(opts.Format)
-
-	return opts, nil
-}
-
-var extensionToLoaderMap = map[string]api.Loader{
-	".js":   api.LoaderJS,
-	".mjs":  api.LoaderJS,
-	".cjs":  api.LoaderJS,
-	".jsx":  api.LoaderJSX,
-	".ts":   api.LoaderTS,
-	".tsx":  api.LoaderTSX,
-	".css":  api.LoaderCSS,
-	".json": api.LoaderJSON,
-	".txt":  api.LoaderText,
-}
-
-func loaderFromFilename(filename string) api.Loader {
-	l, found := extensionToLoaderMap[filepath.Ext(filename)]
-	if found {
-		return l
-	}
-	return api.LoaderJS
-}
-
-func resolveComponentInAssets(fs afero.Fs, impPath string) *hugofs.FileMeta {
-	findFirst := func(base string) *hugofs.FileMeta {
-		// This is the most common sub-set of ESBuild's default extensions.
-		// We assume that imports of JSON, CSS etc. will be using their full
-		// name with extension.
-		for _, ext := range []string{".js", ".ts", ".tsx", ".jsx"} {
-			if strings.HasSuffix(impPath, ext) {
-				// Import of foo.js.js need the full name.
-				continue
-			}
-			if fi, err := fs.Stat(base + ext); err == nil {
-				return fi.(hugofs.FileMetaInfo).Meta()
-			}
-		}
-
-		// Not found.
-		return nil
-	}
-
-	var m *hugofs.FileMeta
-
-	// We need to check if this is a regular file imported without an extension.
-	// There may be ambiguous situations where both foo.js and foo/index.js exists.
-	// This import order is in line with both how Node and ESBuild's native
-	// import resolver works.
-
-	// It may be a regular file imported without an extension, e.g.
-	// foo or foo/index.
-	m = findFirst(impPath)
-	if m != nil {
-		return m
-	}
-
-	base := filepath.Base(impPath)
-	if base == "index" {
-		// try index.esm.js etc.
-		m = findFirst(impPath + ".esm")
-		if m != nil {
-			return m
-		}
-	}
-
-	// Check the path as is.
-	fi, err := fs.Stat(impPath)
-
-	if err == nil {
-		if fi.IsDir() {
-			m = findFirst(filepath.Join(impPath, "index"))
-			if m == nil {
-				m = findFirst(filepath.Join(impPath, "index.esm"))
-			}
-		} else {
-			m = fi.(hugofs.FileMetaInfo).Meta()
-		}
-	} else if strings.HasSuffix(base, ".js") {
-		m = findFirst(strings.TrimSuffix(impPath, ".js"))
-	}
-
-	return m
-}
-
-func createBuildPlugins(depsManager identity.Manager, c *Client, opts Options) ([]api.Plugin, error) {
-	fs := c.rs.Assets
-
-	resolveImport := func(args api.OnResolveArgs) (api.OnResolveResult, error) {
-		impPath := args.Path
-		if opts.Shims != nil {
-			override, found := opts.Shims[impPath]
-			if found {
-				impPath = override
-			}
-		}
-		isStdin := args.Importer == stdinImporter
-		var relDir string
-		if !isStdin {
-			rel, found := fs.MakePathRelative(args.Importer, true)
-			if !found {
-				// Not in any of the /assets folders.
-				// This is an import from a node_modules, let
-				// ESBuild resolve this.
-				return api.OnResolveResult{}, nil
-			}
-
-			relDir = filepath.Dir(rel)
-		} else {
-			relDir = opts.sourceDir
-		}
-
-		// Imports not starting with a "." is assumed to live relative to /assets.
-		// Hugo makes no assumptions about the directory structure below /assets.
-		if relDir != "" && strings.HasPrefix(impPath, ".") {
-			impPath = filepath.Join(relDir, impPath)
-		}
-
-		m := resolveComponentInAssets(fs.Fs, impPath)
-
-		if m != nil {
-			depsManager.AddIdentity(m.PathInfo)
-
-			// Store the source root so we can create a jsconfig.json
-			// to help IntelliSense when the build is done.
-			// This should be a small number of elements, and when
-			// in server mode, we may get stale entries on renames etc.,
-			// but that shouldn't matter too much.
-			c.rs.JSConfigBuilder.AddSourceRoot(m.SourceRoot)
-			return api.OnResolveResult{Path: m.Filename, Namespace: nsImportHugo}, nil
-		}
-
-		// Fall back to ESBuild's resolve.
-		return api.OnResolveResult{}, nil
-	}
-
-	importResolver := api.Plugin{
-		Name: "hugo-import-resolver",
-		Setup: func(build api.PluginBuild) {
-			build.OnResolve(api.OnResolveOptions{Filter: `.*`},
-				func(args api.OnResolveArgs) (api.OnResolveResult, error) {
-					return resolveImport(args)
-				})
-			build.OnLoad(api.OnLoadOptions{Filter: `.*`, Namespace: nsImportHugo},
-				func(args api.OnLoadArgs) (api.OnLoadResult, error) {
-					b, err := os.ReadFile(args.Path)
-					if err != nil {
-						return api.OnLoadResult{}, fmt.Errorf("failed to read %q: %w", args.Path, err)
-					}
-					c := string(b)
-					return api.OnLoadResult{
-						// See https://github.com/evanw/esbuild/issues/502
-						// This allows all modules to resolve dependencies
-						// in the main project's node_modules.
-						ResolveDir: opts.resolveDir,
-						Contents:   &c,
-						Loader:     loaderFromFilename(args.Path),
-					}, nil
-				})
-		},
-	}
-
-	params := opts.Params
-	if params == nil {
-		// This way @params will always resolve to something.
-		params = make(map[string]any)
-	}
-
-	b, err := json.Marshal(params)
-	if err != nil {
-		return nil, fmt.Errorf("failed to marshal params: %w", err)
-	}
-	bs := string(b)
-	paramsPlugin := api.Plugin{
-		Name: "hugo-params-plugin",
-		Setup: func(build api.PluginBuild) {
-			build.OnResolve(api.OnResolveOptions{Filter: `^@params$`},
-				func(args api.OnResolveArgs) (api.OnResolveResult, error) {
-					return api.OnResolveResult{
-						Path:      args.Path,
-						Namespace: nsParams,
-					}, nil
-				})
-			build.OnLoad(api.OnLoadOptions{Filter: `.*`, Namespace: nsParams},
-				func(args api.OnLoadArgs) (api.OnLoadResult, error) {
-					return api.OnLoadResult{
-						Contents: &bs,
-						Loader:   api.LoaderJSON,
-					}, nil
-				})
-		},
-	}
-
-	return []api.Plugin{importResolver, paramsPlugin}, nil
-}
-
-func toBuildOptions(opts Options) (buildOptions api.BuildOptions, err error) {
-	var target api.Target
-	switch opts.Target {
-	case "", "esnext":
-		target = api.ESNext
-	case "es5":
-		target = api.ES5
-	case "es6", "es2015":
-		target = api.ES2015
-	case "es2016":
-		target = api.ES2016
-	case "es2017":
-		target = api.ES2017
-	case "es2018":
-		target = api.ES2018
-	case "es2019":
-		target = api.ES2019
-	case "es2020":
-		target = api.ES2020
-	case "es2021":
-		target = api.ES2021
-	case "es2022":
-		target = api.ES2022
-	case "es2023":
-		target = api.ES2023
-	default:
-		err = fmt.Errorf("invalid target: %q", opts.Target)
-		return
-	}
-
-	mediaType := opts.mediaType
-	if mediaType.IsZero() {
-		mediaType = media.Builtin.JavascriptType
-	}
-
-	var loader api.Loader
-	switch mediaType.SubType {
-	// TODO(bep) ESBuild support a set of other loaders, but I currently fail
-	// to see the relevance. That may change as we start using this.
-	case media.Builtin.JavascriptType.SubType:
-		loader = api.LoaderJS
-	case media.Builtin.TypeScriptType.SubType:
-		loader = api.LoaderTS
-	case media.Builtin.TSXType.SubType:
-		loader = api.LoaderTSX
-	case media.Builtin.JSXType.SubType:
-		loader = api.LoaderJSX
-	default:
-		err = fmt.Errorf("unsupported Media Type: %q", opts.mediaType)
-		return
-	}
-
-	var format api.Format
-	// One of: iife, cjs, esm
-	switch opts.Format {
-	case "", "iife":
-		format = api.FormatIIFE
-	case "esm":
-		format = api.FormatESModule
-	case "cjs":
-		format = api.FormatCommonJS
-	default:
-		err = fmt.Errorf("unsupported script output format: %q", opts.Format)
-		return
-	}
-
-	var jsx api.JSX
-	switch opts.JSX {
-	case "", "transform":
-		jsx = api.JSXTransform
-	case "preserve":
-		jsx = api.JSXPreserve
-	case "automatic":
-		jsx = api.JSXAutomatic
-	default:
-		err = fmt.Errorf("unsupported jsx type: %q", opts.JSX)
-		return
-	}
-
-	var defines map[string]string
-	if opts.Defines != nil {
-		defines = maps.ToStringMapString(opts.Defines)
-	}
-
-	// By default we only need to specify outDir and no outFile
-	outDir := opts.outDir
-	outFile := ""
-	var sourceMap api.SourceMap
-	switch opts.SourceMap {
-	case "inline":
-		sourceMap = api.SourceMapInline
-	case "external":
-		sourceMap = api.SourceMapExternal
-	case "":
-		sourceMap = api.SourceMapNone
-	default:
-		err = fmt.Errorf("unsupported sourcemap type: %q", opts.SourceMap)
-		return
-	}
-
-	buildOptions = api.BuildOptions{
-		Outfile: outFile,
-		Bundle:  true,
-
-		Target:    target,
-		Format:    format,
-		Sourcemap: sourceMap,
-
-		MinifyWhitespace:  opts.Minify,
-		MinifyIdentifiers: opts.Minify,
-		MinifySyntax:      opts.Minify,
-
-		Outdir: outDir,
-		Define: defines,
-
-		External: opts.Externals,
-
-		JSXFactory:  opts.JSXFactory,
-		JSXFragment: opts.JSXFragment,
-
-		JSX:             jsx,
-		JSXImportSource: opts.JSXImportSource,
-
-		Tsconfig: opts.tsConfig,
-
-		// Note: We're not passing Sourcefile to ESBuild.
-		// This makes ESBuild pass `stdin` as the Importer to the import
-		// resolver, which is what we need/expect.
-		Stdin: &api.StdinOptions{
-			Contents:   opts.contents,
-			ResolveDir: opts.resolveDir,
-			Loader:     loader,
-		},
-	}
-	return
-}

resources/resource_transformers/js/options_test.go

@@ -1,241 +0,0 @@
-// Copyright 2020 The Hugo Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package js
-
-import (
-	"path"
-	"path/filepath"
-	"testing"
-
-	"github.com/gohugoio/hugo/config"
-	"github.com/gohugoio/hugo/config/testconfig"
-	"github.com/gohugoio/hugo/hugofs"
-	"github.com/gohugoio/hugo/hugolib/filesystems"
-	"github.com/gohugoio/hugo/hugolib/paths"
-	"github.com/gohugoio/hugo/media"
-
-	"github.com/spf13/afero"
-
-	"github.com/evanw/esbuild/pkg/api"
-
-	qt "github.com/frankban/quicktest"
-)
-
-// This test is added to test/warn against breaking the "stability" of the
-// cache key. It's sometimes needed to break this, but should be avoided if possible.
-func TestOptionKey(t *testing.T) {
-	c := qt.New(t)
-
-	opts := map[string]any{
-		"TargetPath": "foo",
-		"Target":     "es2018",
-	}
-
-	key := (&buildTransformation{optsm: opts}).Key()
-
-	c.Assert(key.Value(), qt.Equals, "jsbuild_1533819657654811600")
-}
-
-func TestToBuildOptions(t *testing.T) {
-	c := qt.New(t)
-
-	opts, err := toBuildOptions(Options{mediaType: media.Builtin.JavascriptType})
-
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle: true,
-		Target: api.ESNext,
-		Format: api.FormatIIFE,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-	})
-
-	opts, err = toBuildOptions(Options{
-		Target:    "es2018",
-		Format:    "cjs",
-		Minify:    true,
-		mediaType: media.Builtin.JavascriptType,
-		AvoidTDZ:  true,
-	})
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle:            true,
-		Target:            api.ES2018,
-		Format:            api.FormatCommonJS,
-		MinifyIdentifiers: true,
-		MinifySyntax:      true,
-		MinifyWhitespace:  true,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-	})
-
-	opts, err = toBuildOptions(Options{
-		Target: "es2018", Format: "cjs", Minify: true, mediaType: media.Builtin.JavascriptType,
-		SourceMap: "inline",
-	})
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle:            true,
-		Target:            api.ES2018,
-		Format:            api.FormatCommonJS,
-		MinifyIdentifiers: true,
-		MinifySyntax:      true,
-		MinifyWhitespace:  true,
-		Sourcemap:         api.SourceMapInline,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-	})
-
-	opts, err = toBuildOptions(Options{
-		Target: "es2018", Format: "cjs", Minify: true, mediaType: media.Builtin.JavascriptType,
-		SourceMap: "inline",
-	})
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle:            true,
-		Target:            api.ES2018,
-		Format:            api.FormatCommonJS,
-		MinifyIdentifiers: true,
-		MinifySyntax:      true,
-		MinifyWhitespace:  true,
-		Sourcemap:         api.SourceMapInline,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-	})
-
-	opts, err = toBuildOptions(Options{
-		Target: "es2018", Format: "cjs", Minify: true, mediaType: media.Builtin.JavascriptType,
-		SourceMap: "external",
-	})
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle:            true,
-		Target:            api.ES2018,
-		Format:            api.FormatCommonJS,
-		MinifyIdentifiers: true,
-		MinifySyntax:      true,
-		MinifyWhitespace:  true,
-		Sourcemap:         api.SourceMapExternal,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-	})
-
-	opts, err = toBuildOptions(Options{
-		mediaType: media.Builtin.JavascriptType,
-		JSX:       "automatic", JSXImportSource: "preact",
-	})
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle: true,
-		Target: api.ESNext,
-		Format: api.FormatIIFE,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-		JSX:             api.JSXAutomatic,
-		JSXImportSource: "preact",
-	})
-}
-
-func TestToBuildOptionsTarget(t *testing.T) {
-	c := qt.New(t)
-
-	for _, test := range []struct {
-		target string
-		expect api.Target
-	}{
-		{"es2015", api.ES2015},
-		{"es2016", api.ES2016},
-		{"es2017", api.ES2017},
-		{"es2018", api.ES2018},
-		{"es2019", api.ES2019},
-		{"es2020", api.ES2020},
-		{"es2021", api.ES2021},
-		{"es2022", api.ES2022},
-		{"es2023", api.ES2023},
-		{"", api.ESNext},
-		{"esnext", api.ESNext},
-	} {
-		c.Run(test.target, func(c *qt.C) {
-			opts, err := toBuildOptions(Options{
-				Target:    test.target,
-				mediaType: media.Builtin.JavascriptType,
-			})
-			c.Assert(err, qt.IsNil)
-			c.Assert(opts.Target, qt.Equals, test.expect)
-		})
-	}
-}
-
-func TestResolveComponentInAssets(t *testing.T) {
-	c := qt.New(t)
-
-	for _, test := range []struct {
-		name    string
-		files   []string
-		impPath string
-		expect  string
-	}{
-		{"Basic, extension", []string{"foo.js", "bar.js"}, "foo.js", "foo.js"},
-		{"Basic, no extension", []string{"foo.js", "bar.js"}, "foo", "foo.js"},
-		{"Basic, no extension, typescript", []string{"foo.ts", "bar.js"}, "foo", "foo.ts"},
-		{"Not found", []string{"foo.js", "bar.js"}, "moo.js", ""},
-		{"Not found, double js extension", []string{"foo.js.js", "bar.js"}, "foo.js", ""},
-		{"Index file, folder only", []string{"foo/index.js", "bar.js"}, "foo", "foo/index.js"},
-		{"Index file, folder and index", []string{"foo/index.js", "bar.js"}, "foo/index", "foo/index.js"},
-		{"Index file, folder and index and suffix", []string{"foo/index.js", "bar.js"}, "foo/index.js", "foo/index.js"},
-		{"Index ESM file, folder only", []string{"foo/index.esm.js", "bar.js"}, "foo", "foo/index.esm.js"},
-		{"Index ESM file, folder and index", []string{"foo/index.esm.js", "bar.js"}, "foo/index", "foo/index.esm.js"},
-		{"Index ESM file, folder and index and suffix", []string{"foo/index.esm.js", "bar.js"}, "foo/index.esm.js", "foo/index.esm.js"},
-		// We added these index.esm.js cases in v0.101.0. The case below is unlikely to happen in the wild, but add a test
-		// to document Hugo's behavior. We pick the file with the name index.js; anything else would be breaking.
-		{"Index and Index ESM file, folder only", []string{"foo/index.esm.js", "foo/index.js", "bar.js"}, "foo", "foo/index.js"},
-
-		// Issue #8949
-		{"Check file before directory", []string{"foo.js", "foo/index.js"}, "foo", "foo.js"},
-	} {
-		c.Run(test.name, func(c *qt.C) {
-			baseDir := "assets"
-			mfs := afero.NewMemMapFs()
-
-			for _, filename := range test.files {
-				c.Assert(afero.WriteFile(mfs, filepath.Join(baseDir, filename), []byte("let foo='bar';"), 0o777), qt.IsNil)
-			}
-
-			conf := testconfig.GetTestConfig(mfs, config.New())
-			fs := hugofs.NewFrom(mfs, conf.BaseConfig())
-
-			p, err := paths.New(fs, conf)
-			c.Assert(err, qt.IsNil)
-			bfs, err := filesystems.NewBase(p, nil)
-			c.Assert(err, qt.IsNil)
-
-			got := resolveComponentInAssets(bfs.Assets.Fs, test.impPath)
-
-			gotPath := ""
-			expect := test.expect
-			if got != nil {
-				gotPath = filepath.ToSlash(got.Filename)
-				expect = path.Join(baseDir, test.expect)
-			}
-
-			c.Assert(gotPath, qt.Equals, expect)
-		})
-	}
-}

resources/resource_transformers/js/transform.go

@@ -0,0 +1,68 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package js
+
+import (
+	"io"
+	"path"
+	"path/filepath"
+
+	"github.com/gohugoio/hugo/internal/js/esbuild"
+	"github.com/gohugoio/hugo/media"
+	"github.com/gohugoio/hugo/resources"
+	"github.com/gohugoio/hugo/resources/internal"
+)
+
+type buildTransformation struct {
+	optsm map[string]any
+	c     *Client
+}
+
+func (t *buildTransformation) Key() internal.ResourceTransformationKey {
+	return internal.NewResourceTransformationKey("jsbuild", t.optsm)
+}
+
+func (t *buildTransformation) Transform(ctx *resources.ResourceTransformationCtx) error {
+	ctx.OutMediaType = media.Builtin.JavascriptType
+
+	var opts esbuild.Options
+
+	if t.optsm != nil {
+		optsExt, err := esbuild.DecodeExternalOptions(t.optsm)
+		if err != nil {
+			return err
+		}
+		opts.ExternalOptions = optsExt
+	}
+
+	if opts.TargetPath != "" {
+		ctx.OutPath = opts.TargetPath
+	} else {
+		ctx.ReplaceOutPathExtension(".js")
+	}
+
+	src, err := io.ReadAll(ctx.From)
+	if err != nil {
+		return err
+	}
+
+	opts.SourceDir = filepath.FromSlash(path.Dir(ctx.SourcePath))
+	opts.Contents = string(src)
+	opts.MediaType = ctx.InMediaType
+	opts.Stdin = true
+
+	_, err = t.c.transform(opts, ctx)
+
+	return err
+}

resources/transform.go

@@ -52,6 +52,7 @@ var (
 	_ identity.IdentityGroupProvider     = (*resourceAdapterInner)(nil)
 	_ resource.Source                    = (*resourceAdapter)(nil)
 	_ resource.Identifier                = (*resourceAdapter)(nil)
+	_ resource.PathProvider              = (*resourceAdapter)(nil)
 	_ resource.ResourceNameTitleProvider = (*resourceAdapter)(nil)
 	_ resource.WithResourceMetaProvider  = (*resourceAdapter)(nil)
 	_ identity.DependencyManagerProvider = (*resourceAdapter)(nil)
@@ -277,6 +278,11 @@ func (r *resourceAdapter) Key() string {
 	return r.target.(resource.Identifier).Key()
 }
 
+func (r *resourceAdapter) Path() string {
+	r.init(false, false)
+	return r.target.(resource.PathProvider).Path()
+}
+
 func (r *resourceAdapter) MediaType() media.Type {
 	r.init(false, false)
 	return r.target.MediaType()

tpl/js/init.go

@@ -24,7 +24,10 @@ const name = "js"
 
 func init() {
 	f := func(d *deps.Deps) *internal.TemplateFuncsNamespace {
-		ctx := New(d)
+		ctx, err := New(d)
+		if err != nil {
+			panic(err)
+		}
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,

tpl/js/js.go

@@ -1,4 +1,4 @@
-// Copyright 2020 The Hugo Authors. All rights reserved.
+// Copyright 2024 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -16,30 +16,47 @@ package js
 
 import (
 	"errors"
+	"path"
 
+	"github.com/gohugoio/hugo/common/maps"
 	"github.com/gohugoio/hugo/deps"
+	"github.com/gohugoio/hugo/internal/js/esbuild"
 	"github.com/gohugoio/hugo/resources"
 	"github.com/gohugoio/hugo/resources/resource"
+	"github.com/gohugoio/hugo/resources/resource_factories/create"
 	"github.com/gohugoio/hugo/resources/resource_transformers/babel"
-	"github.com/gohugoio/hugo/resources/resource_transformers/js"
+	jstransform "github.com/gohugoio/hugo/resources/resource_transformers/js"
 	"github.com/gohugoio/hugo/tpl/internal/resourcehelpers"
 )
 
 // New returns a new instance of the js-namespaced template functions.
-func New(deps *deps.Deps) *Namespace {
+func New(deps *deps.Deps) (*Namespace, error) {
 	if deps.ResourceSpec == nil {
-		return &Namespace{}
+		return &Namespace{}, nil
 	}
+
+	batcherClient, err := esbuild.NewBatcherClient(deps)
+	if err != nil {
+		return nil, err
+	}
+
 	return &Namespace{
-		client:      js.New(deps.BaseFs.Assets, deps.ResourceSpec),
-		babelClient: babel.New(deps.ResourceSpec),
-	}
+		d:                 deps,
+		jsTransformClient: jstransform.New(deps.BaseFs.Assets, deps.ResourceSpec),
+		jsBatcherClient:   batcherClient,
+		createClient:      create.New(deps.ResourceSpec),
+		babelClient:       babel.New(deps.ResourceSpec),
+	}, nil
 }
 
 // Namespace provides template functions for the "js" namespace.
 type Namespace struct {
-	client      *js.Client
-	babelClient *babel.Client
+	d *deps.Deps
+
+	jsTransformClient *jstransform.Client
+	createClient      *create.Client
+	babelClient       *babel.Client
+	jsBatcherClient   *esbuild.BatcherClient
 }
 
 // Build processes the given Resource with ESBuild.
@@ -65,7 +82,18 @@ func (ns *Namespace) Build(args ...any) (resource.Resource, error) {
 		m = map[string]any{"targetPath": targetPath}
 	}
 
-	return ns.client.Process(r, m)
+	return ns.jsTransformClient.Process(r, m)
+}
+
+func (ns *Namespace) Batch(id string, store *maps.Scratch) (esbuild.Batcher, error) {
+	key := path.Join(esbuild.NsBatch, id)
+	b, err := store.GetOrCreate(key, func() (any, error) {
+		return ns.jsBatcherClient.New(id)
+	})
+	if err != nil {
+		return nil, err
+	}
+	return b.(esbuild.Batcher), nil
 }
 
 // Babel processes the given Resource with Babel.

tpl/tplimpl/embedded/templates/_hugo/build/js/batch-esm-runner.gotmpl

@@ -0,0 +1,16 @@
+{{ range $i, $e := .Scripts -}}
+  {{ printf "import { %s as Script%d } from %q;" .Export $i .Import }}
+{{ end -}}
+{{ range $i, $e := .Runners }}
+  {{ printf "import { %s as Run%d } from %q;" .Export $i .Import }}
+{{ end }}
+{{/*  */}}
+let scripts = [];
+{{ range $i, $e := .Scripts -}}
+  scripts.push({{ .RunnerJSON $i }});
+{{ end -}}
+{{/*  */}}
+{{ range $i, $e := .Runners }}
+  {{ $id := printf "Run%d" $i }}
+  {{ $id }}(scripts);
+{{ end }}