tpl/partials: Fix recently introduced deadlock in partials cache

The change in lock logic for `partialCached` in  0927cf739f was naive as it didn't consider cached partials calling other cached partials.

This changeset may look on the large side for this particular issue, but it pulls in part of a working branch, introducing `context.Context` in the template execution.

Note that the context is only partially implemented in this PR, but the upcoming use cases will, as one example, include having access to the top "dot" (e.g. `Page`) all the way down into partials and shortcodes etc.

The earlier benchmarks rerun against master:

```bash
name              old time/op    new time/op    delta
IncludeCached-10    13.6ms ± 2%    13.8ms ± 1%    ~     (p=0.343 n=4+4)

name              old alloc/op   new alloc/op   delta
IncludeCached-10    5.30MB ± 0%    5.35MB ± 0%  +0.96%  (p=0.029 n=4+4)

name              old allocs/op  new allocs/op  delta
IncludeCached-10     74.7k ± 0%     75.3k ± 0%  +0.77%  (p=0.029 n=4+4)
```

Fixes #9519

tpl/collections/apply_test.go

@@ -14,6 +14,7 @@
 package collections
 
 import (
+	"context"
 	"fmt"
 	"io"
 	"reflect"
@@ -51,6 +52,10 @@ func (templateFinder) Execute(t tpl.Template, wr io.Writer, data interface{}) er
 	return nil
 }
 
+func (templateFinder) ExecuteWithContext(ctx context.Context, t tpl.Template, wr io.Writer, data interface{}) error {
+	return nil
+}
+
 func (templateFinder) GetFunc(name string) (reflect.Value, bool) {
 	if name == "dobedobedo" {
 		return reflect.Value{}, false

tpl/internal/go_templates/texttemplate/hugo_template.go

@@ -1,4 +1,4 @@
-// Copyright 2019 The Hugo Authors. All rights reserved.
+// Copyright 2022 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.
@@ -14,6 +14,7 @@
 package template
 
 import (
+	"context"
 	"io"
 	"reflect"
 
@@ -39,14 +40,15 @@ type Preparer interface {
 
 // ExecHelper allows some custom eval hooks.
 type ExecHelper interface {
-	GetFunc(tmpl Preparer, name string) (reflect.Value, bool)
+	Init(ctx context.Context, tmpl Preparer)
-	GetMethod(tmpl Preparer, receiver reflect.Value, name string) (method reflect.Value, firstArg reflect.Value)
+	GetFunc(ctx context.Context, tmpl Preparer, name string) (reflect.Value, reflect.Value, bool)
-	GetMapValue(tmpl Preparer, receiver, key reflect.Value) (reflect.Value, bool)
+	GetMethod(ctx context.Context, tmpl Preparer, receiver reflect.Value, name string) (method reflect.Value, firstArg reflect.Value)
+	GetMapValue(ctx context.Context, tmpl Preparer, receiver, key reflect.Value) (reflect.Value, bool)
 }
 
 // Executer executes a given template.
 type Executer interface {
-	Execute(p Preparer, wr io.Writer, data interface{}) error
+	ExecuteWithContext(ctx context.Context, p Preparer, wr io.Writer, data interface{}) error
 }
 
 type executer struct {
@@ -57,6 +59,48 @@ func NewExecuter(helper ExecHelper) Executer {
 	return &executer{helper: helper}
 }
 
+type (
+	dataContextKeyType    string
+	hasLockContextKeyType string
+)
+
+const (
+	// The data object passed to Execute or ExecuteWithContext gets stored with this key if not already set.
+	DataContextKey = dataContextKeyType("data")
+	// Used in partialCached to signal to nested templates that a lock is already taken.
+	HasLockContextKey = hasLockContextKeyType("hasLock")
+)
+
+// Note: The context is currently not fully implemeted in Hugo. This is a work in progress.
+func (t *executer) ExecuteWithContext(ctx context.Context, p Preparer, wr io.Writer, data interface{}) error {
+	tmpl, err := p.Prepare()
+	if err != nil {
+		return err
+	}
+
+	if v := ctx.Value(DataContextKey); v == nil {
+		ctx = context.WithValue(ctx, DataContextKey, data)
+	}
+
+	value, ok := data.(reflect.Value)
+	if !ok {
+		value = reflect.ValueOf(data)
+	}
+
+	state := &state{
+		ctx:    ctx,
+		helper: t.helper,
+		prep:   p,
+		tmpl:   tmpl,
+		wr:     wr,
+		vars:   []variable{{"$", value}},
+	}
+
+	t.helper.Init(ctx, p)
+
+	return tmpl.executeWithState(state, value)
+}
+
 func (t *executer) Execute(p Preparer, wr io.Writer, data interface{}) error {
 	tmpl, err := p.Prepare()
 	if err != nil {
@@ -77,7 +121,6 @@ func (t *executer) Execute(p Preparer, wr io.Writer, data interface{}) error {
 	}
 
 	return tmpl.executeWithState(state, value)
-
 }
 
 // Prepare returns a template ready for execution.
@@ -101,8 +144,9 @@ func (t *Template) executeWithState(state *state, value reflect.Value) (err erro
 // can execute in parallel.
 type state struct {
 	tmpl   *Template
-	prep   Preparer   // Added for Hugo.
+	ctx    context.Context // Added for Hugo. The orignal data context.
-	helper ExecHelper // Added for Hugo.
+	prep   Preparer        // Added for Hugo.
+	helper ExecHelper      // Added for Hugo.
 	wr     io.Writer
 	node   parse.Node // current node, for errors
 	vars   []variable // push-down stack of variable values.
@@ -114,10 +158,11 @@ func (s *state) evalFunction(dot reflect.Value, node *parse.IdentifierNode, cmd
 	name := node.Ident
 
 	var function reflect.Value
+	// Added for Hugo.
+	var first reflect.Value
 	var ok bool
 	if s.helper != nil {
-		// Added for Hugo.
+		function, first, ok = s.helper.GetFunc(s.ctx, s.prep, name)
-		function, ok = s.helper.GetFunc(s.prep, name)
 	}
 
 	if !ok {
@@ -127,6 +172,9 @@ func (s *state) evalFunction(dot reflect.Value, node *parse.IdentifierNode, cmd
 	if !ok {
 		s.errorf("%q is not a defined function", name)
 	}
+	if first != zero {
+		return s.evalCall(dot, function, cmd, name, args, final, first)
+	}
 	return s.evalCall(dot, function, cmd, name, args, final)
 }
 
@@ -159,7 +207,7 @@ func (s *state) evalField(dot reflect.Value, fieldName string, node parse.Node,
 	var first reflect.Value
 	var method reflect.Value
 	if s.helper != nil {
-		method, first = s.helper.GetMethod(s.prep, ptr, fieldName)
+		method, first = s.helper.GetMethod(s.ctx, s.prep, ptr, fieldName)
 	} else {
 		method = ptr.MethodByName(fieldName)
 	}
@@ -198,7 +246,7 @@ func (s *state) evalField(dot reflect.Value, fieldName string, node parse.Node,
 			var result reflect.Value
 			if s.helper != nil {
 				// Added for Hugo.
-				result, _ = s.helper.GetMapValue(s.prep, receiver, nameVal)
+				result, _ = s.helper.GetMapValue(s.ctx, s.prep, receiver, nameVal)
 			} else {
 				result = receiver.MapIndex(nameVal)
 			}

tpl/internal/go_templates/texttemplate/hugo_template_test.go

@@ -1,4 +1,4 @@
-// Copyright 2019 The Hugo Authors. All rights reserved.
+// Copyright 2022 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.
@@ -15,6 +15,7 @@ package template
 
 import (
 	"bytes"
+	"context"
 	"reflect"
 	"strings"
 	"testing"
@@ -35,24 +36,26 @@ func (t TestStruct) Hello2(arg1, arg2 string) string {
 	return arg1 + " " + arg2
 }
 
-type execHelper struct {
+type execHelper struct{}
+
+func (e *execHelper) Init(ctx context.Context, tmpl Preparer) {
 }
 
-func (e *execHelper) GetFunc(tmpl Preparer, name string) (reflect.Value, bool) {
+func (e *execHelper) GetFunc(ctx context.Context, tmpl Preparer, name string) (reflect.Value, reflect.Value, bool) {
 	if name == "print" {
-		return zero, false
+		return zero, zero, false
 	}
 	return reflect.ValueOf(func(s string) string {
 		return "hello " + s
-	}), true
+	}), zero, true
 }
 
-func (e *execHelper) GetMapValue(tmpl Preparer, m, key reflect.Value) (reflect.Value, bool) {
+func (e *execHelper) GetMapValue(ctx context.Context, tmpl Preparer, m, key reflect.Value) (reflect.Value, bool) {
 	key = reflect.ValueOf(strings.ToLower(key.String()))
 	return m.MapIndex(key), true
 }
 
-func (e *execHelper) GetMethod(tmpl Preparer, receiver reflect.Value, name string) (method reflect.Value, firstArg reflect.Value) {
+func (e *execHelper) GetMethod(ctx context.Context, tmpl Preparer, receiver reflect.Value, name string) (method reflect.Value, firstArg reflect.Value) {
 	if name != "Hello1" {
 		return zero, zero
 	}
@@ -78,12 +81,11 @@ Method: {{ .Hello1 "v1" }}
 	var b bytes.Buffer
 	data := TestStruct{S: "sv", M: map[string]string{"a": "av"}}
 
-	c.Assert(ex.Execute(templ, &b, data), qt.IsNil)
+	c.Assert(ex.ExecuteWithContext(context.Background(), templ, &b, data), qt.IsNil)
 	got := b.String()
 
 	c.Assert(got, qt.Contains, "foo")
 	c.Assert(got, qt.Contains, "hello hugo")
 	c.Assert(got, qt.Contains, "Map: av")
 	c.Assert(got, qt.Contains, "Method: v2 v1")
-
 }

tpl/partials/integration_test.go

@@ -75,6 +75,34 @@ partialCached: foo
 `)
 }
 
+// Issue 9519
+func TestIncludeCachedRecursion(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- config.toml --
+baseURL = 'http://example.com/'
+-- layouts/index.html --
+{{ partials.IncludeCached "p1.html" . }}
+-- layouts/partials/p1.html --
+{{ partials.IncludeCached "p2.html" . }}
+-- layouts/partials/p2.html --
+P2
+
+  `
+
+	b := hugolib.NewIntegrationTestBuilder(
+		hugolib.IntegrationTestConfig{
+			T:           t,
+			TxtarString: files,
+		},
+	).Build()
+
+	b.AssertFileContent("public/index.html", `
+P2
+`)
+}
+
 func TestIncludeCacheHints(t *testing.T) {
 	t.Parallel()
 

tpl/partials/partials.go

@@ -16,6 +16,7 @@
 package partials
 
 import (
+	"context"
 	"errors"
 	"fmt"
 	"html/template"
@@ -100,8 +101,9 @@ func (c *contextWrapper) Set(in interface{}) string {
 // If the partial contains a return statement, that value will be returned.
 // Else, the rendered output will be returned:
 // A string if the partial is a text/template, or template.HTML when html/template.
-func (ns *Namespace) Include(name string, contextList ...interface{}) (interface{}, error) {
+// Note that ctx is provided by Hugo, not the end user.
-	name, result, err := ns.include(name, contextList...)
+func (ns *Namespace) Include(ctx context.Context, name string, contextList ...interface{}) (interface{}, error) {
+	name, result, err := ns.include(ctx, name, contextList...)
 	if err != nil {
 		return result, err
 	}
@@ -115,10 +117,10 @@ func (ns *Namespace) Include(name string, contextList ...interface{}) (interface
 
 // include is a helper function that lookups and executes the named partial.
 // Returns the final template name and the rendered output.
-func (ns *Namespace) include(name string, contextList ...interface{}) (string, interface{}, error) {
+func (ns *Namespace) include(ctx context.Context, name string, dataList ...interface{}) (string, interface{}, error) {
-	var context interface{}
+	var data interface{}
-	if len(contextList) > 0 {
+	if len(dataList) > 0 {
-		context = contextList[0]
+		data = dataList[0]
 	}
 
 	var n string
@@ -149,8 +151,8 @@ func (ns *Namespace) include(name string, contextList ...interface{}) (string, i
 		// Wrap the context sent to the template to capture the return value.
 		// Note that the template is rewritten to make sure that the dot (".")
 		// and the $ variable points to Arg.
-		context = &contextWrapper{
+		data = &contextWrapper{
-			Arg: context,
+			Arg: data,
 		}
 
 		// We don't care about any template output.
@@ -161,13 +163,13 @@ func (ns *Namespace) include(name string, contextList ...interface{}) (string, i
 		w = b
 	}
 
-	if err := ns.deps.Tmpl().Execute(templ, w, context); err != nil {
+	if err := ns.deps.Tmpl().ExecuteWithContext(ctx, templ, w, data); err != nil {
-		return "", "", err
+		return "", nil, err
 	}
 
 	var result interface{}
 
-	if ctx, ok := context.(*contextWrapper); ok {
+	if ctx, ok := data.(*contextWrapper); ok {
 		result = ctx.Result
 	} else if _, ok := templ.(*texttemplate.Template); ok {
 		result = w.(fmt.Stringer).String()
@@ -179,17 +181,18 @@ func (ns *Namespace) include(name string, contextList ...interface{}) (string, i
 }
 
 // IncludeCached executes and caches partial templates.  The cache is created with name+variants as the key.
-func (ns *Namespace) IncludeCached(name string, context interface{}, variants ...interface{}) (interface{}, error) {
+// Note that ctx is provided by Hugo, not the end user.
+func (ns *Namespace) IncludeCached(ctx context.Context, name string, context interface{}, variants ...interface{}) (interface{}, error) {
 	key, err := createKey(name, variants...)
 	if err != nil {
 		return nil, err
 	}
 
-	result, err := ns.getOrCreate(key, context)
+	result, err := ns.getOrCreate(ctx, key, context)
 	if err == errUnHashable {
 		// Try one more
 		key.variant = helpers.HashString(key.variant)
-		result, err = ns.getOrCreate(key, context)
+		result, err = ns.getOrCreate(ctx, key, context)
 	}
 
 	return result, err
@@ -218,7 +221,7 @@ func createKey(name string, variants ...interface{}) (partialCacheKey, error) {
 
 var errUnHashable = errors.New("unhashable")
 
-func (ns *Namespace) getOrCreate(key partialCacheKey, context interface{}) (result interface{}, err error) {
+func (ns *Namespace) getOrCreate(ctx context.Context, key partialCacheKey, context interface{}) (result interface{}, err error) {
 	start := time.Now()
 	defer func() {
 		if r := recover(); r != nil {
@@ -230,9 +233,16 @@ func (ns *Namespace) getOrCreate(key partialCacheKey, context interface{}) (resu
 		}
 	}()
 
-	ns.cachedPartials.RLock()
+	// We may already have a write lock.
+	hasLock := tpl.GetHasLockFromContext(ctx)
+
+	if !hasLock {
+		ns.cachedPartials.RLock()
+	}
 	p, ok := ns.cachedPartials.p[key]
-	ns.cachedPartials.RUnlock()
+	if !hasLock {
+		ns.cachedPartials.RUnlock()
+	}
 
 	if ok {
 		if ns.deps.Metrics != nil {
@@ -246,11 +256,14 @@ func (ns *Namespace) getOrCreate(key partialCacheKey, context interface{}) (resu
 		return p, nil
 	}
 
-	ns.cachedPartials.Lock()
+	if !hasLock {
-	defer ns.cachedPartials.Unlock()
+		ns.cachedPartials.Lock()
+		defer ns.cachedPartials.Unlock()
+		ctx = tpl.SetHasLockInContext(ctx, true)
+	}
 
 	var name string
-	name, p, err = ns.include(key.name, context)
+	name, p, err = ns.include(ctx, key.name, context)
 	if err != nil {
 		return nil, err
 	}

tpl/template.go

@@ -14,6 +14,7 @@
 package tpl
 
 import (
+	"context"
 	"io"
 	"reflect"
 	"regexp"
@@ -53,6 +54,7 @@ type UnusedTemplatesProvider interface {
 type TemplateHandler interface {
 	TemplateFinder
 	Execute(t Template, wr io.Writer, data interface{}) error
+	ExecuteWithContext(ctx context.Context, t Template, wr io.Writer, data interface{}) error
 	LookupLayout(d output.LayoutDescriptor, f output.Format) (Template, bool, error)
 	HasTemplate(name string) bool
 }
@@ -144,3 +146,20 @@ func extractBaseOf(err string) string {
 type TemplateFuncGetter interface {
 	GetFunc(name string) (reflect.Value, bool)
 }
+
+// GetDataFromContext returns the template data context (usually .Page) from ctx if set.
+// NOte: This is not fully implemented yet.
+func GetDataFromContext(ctx context.Context) interface{} {
+	return ctx.Value(texttemplate.DataContextKey)
+}
+
+func GetHasLockFromContext(ctx context.Context) bool {
+	if v := ctx.Value(texttemplate.HasLockContextKey); v != nil {
+		return v.(bool)
+	}
+	return false
+}
+
+func SetHasLockInContext(ctx context.Context, hasLock bool) context.Context {
+	return context.WithValue(ctx, texttemplate.HasLockContextKey, hasLock)
+}

tpl/tplimpl/template.go

@@ -15,6 +15,7 @@ package tplimpl
 
 import (
 	"bytes"
+	"context"
 	"embed"
 	"io"
 	"io/fs"
@@ -225,6 +226,10 @@ func (t templateExec) Clone(d *deps.Deps) *templateExec {
 }
 
 func (t *templateExec) Execute(templ tpl.Template, wr io.Writer, data interface{}) error {
+	return t.ExecuteWithContext(context.Background(), templ, wr, data)
+}
+
+func (t *templateExec) ExecuteWithContext(ctx context.Context, templ tpl.Template, wr io.Writer, data interface{}) error {
 	if rlocker, ok := templ.(types.RLocker); ok {
 		rlocker.RLock()
 		defer rlocker.RUnlock()
@@ -249,11 +254,10 @@ func (t *templateExec) Execute(templ tpl.Template, wr io.Writer, data interface{
 		}
 	}
 
-	execErr := t.executor.Execute(templ, wr, data)
+	execErr := t.executor.ExecuteWithContext(ctx, templ, wr, data)
 	if execErr != nil {
 		execErr = t.addFileContext(templ, execErr)
 	}
-
 	return execErr
 }
 

tpl/tplimpl/template_funcs.go

@@ -16,6 +16,7 @@
 package tplimpl
 
 import (
+	"context"
 	"reflect"
 	"strings"
 
@@ -61,8 +62,9 @@ import (
 )
 
 var (
-	_    texttemplate.ExecHelper = (*templateExecHelper)(nil)
+	_                texttemplate.ExecHelper = (*templateExecHelper)(nil)
-	zero reflect.Value
+	zero             reflect.Value
+	contextInterface = reflect.TypeOf((*context.Context)(nil)).Elem()
 )
 
 type templateExecHelper struct {
@@ -70,14 +72,27 @@ type templateExecHelper struct {
 	funcs   map[string]reflect.Value
 }
 
-func (t *templateExecHelper) GetFunc(tmpl texttemplate.Preparer, name string) (reflect.Value, bool) {
+func (t *templateExecHelper) GetFunc(ctx context.Context, tmpl texttemplate.Preparer, name string) (fn reflect.Value, firstArg reflect.Value, found bool) {
 	if fn, found := t.funcs[name]; found {
-		return fn, true
+		if fn.Type().NumIn() > 0 {
+			first := fn.Type().In(0)
+			if first.Implements(contextInterface) {
+				// TODO(bep) check if we can void this conversion every time -- and if that matters.
+				// The first argument may be context.Context. This is never provided by the end user, but it's used to pass down
+				// contextual information, e.g. the top level data context (e.g. Page).
+				return fn, reflect.ValueOf(ctx), true
+			}
+		}
+
+		return fn, zero, true
 	}
-	return zero, false
+	return zero, zero, false
 }
 
-func (t *templateExecHelper) GetMapValue(tmpl texttemplate.Preparer, receiver, key reflect.Value) (reflect.Value, bool) {
+func (t *templateExecHelper) Init(ctx context.Context, tmpl texttemplate.Preparer) {
+}
+
+func (t *templateExecHelper) GetMapValue(ctx context.Context, tmpl texttemplate.Preparer, receiver, key reflect.Value) (reflect.Value, bool) {
 	if params, ok := receiver.Interface().(maps.Params); ok {
 		// Case insensitive.
 		keystr := strings.ToLower(key.String())
@@ -93,10 +108,11 @@ func (t *templateExecHelper) GetMapValue(tmpl texttemplate.Preparer, receiver, k
 	return v, v.IsValid()
 }
 
-func (t *templateExecHelper) GetMethod(tmpl texttemplate.Preparer, receiver reflect.Value, name string) (method reflect.Value, firstArg reflect.Value) {
+func (t *templateExecHelper) GetMethod(ctx context.Context, tmpl texttemplate.Preparer, receiver reflect.Value, name string) (method reflect.Value, firstArg reflect.Value) {
 	if t.running {
 		// This is a hot path and receiver.MethodByName really shows up in the benchmarks,
 		// so we maintain a list of method names with that signature.
+		// TODO(bep) I have a branch that makes this construct superflous.
 		switch name {
 		case "GetPage", "Render":
 			if info, ok := tmpl.(tpl.Info); ok {
@@ -107,7 +123,21 @@ func (t *templateExecHelper) GetMethod(tmpl texttemplate.Preparer, receiver refl
 		}
 	}
 
-	return receiver.MethodByName(name), zero
+	fn := receiver.MethodByName(name)
+	if !fn.IsValid() {
+		return zero, zero
+	}
+
+	if fn.Type().NumIn() > 0 {
+		first := fn.Type().In(0)
+		if first.Implements(contextInterface) {
+			// The first argument may be context.Context. This is never provided by the end user, but it's used to pass down
+			// contextual information, e.g. the top level data context (e.g. Page).
+			return fn, reflect.ValueOf(ctx)
+		}
+	}
+
+	return fn, zero
 }
 
 func newTemplateExecuter(d *deps.Deps) (texttemplate.Executer, map[string]reflect.Value) {

tpl/tplimpl/template_funcs_test.go

@@ -15,6 +15,7 @@ package tplimpl
 
 import (
 	"bytes"
+	"context"
 	"fmt"
 	"path/filepath"
 	"reflect"
@@ -145,8 +146,7 @@ func TestPartialCached(t *testing.T) {
 	partial := `Now: {{ now.UnixNano }}`
 	name := "testing"
 
-	var data struct {
+	var data struct{}
-	}
 
 	v := newTestConfig()
 
@@ -168,19 +168,19 @@ func TestPartialCached(t *testing.T) {
 
 	ns := partials.New(de)
 
-	res1, err := ns.IncludeCached(name, &data)
+	res1, err := ns.IncludeCached(context.Background(), name, &data)
 	c.Assert(err, qt.IsNil)
 
 	for j := 0; j < 10; j++ {
 		time.Sleep(2 * time.Nanosecond)
-		res2, err := ns.IncludeCached(name, &data)
+		res2, err := ns.IncludeCached(context.Background(), name, &data)
 		c.Assert(err, qt.IsNil)
 
 		if !reflect.DeepEqual(res1, res2) {
 			t.Fatalf("cache mismatch")
 		}
 
-		res3, err := ns.IncludeCached(name, &data, fmt.Sprintf("variant%d", j))
+		res3, err := ns.IncludeCached(context.Background(), name, &data, fmt.Sprintf("variant%d", j))
 		c.Assert(err, qt.IsNil)
 
 		if reflect.DeepEqual(res1, res3) {
@@ -191,14 +191,14 @@ func TestPartialCached(t *testing.T) {
 
 func BenchmarkPartial(b *testing.B) {
 	doBenchmarkPartial(b, func(ns *partials.Namespace) error {
-		_, err := ns.Include("bench1")
+		_, err := ns.Include(context.Background(), "bench1")
 		return err
 	})
 }
 
 func BenchmarkPartialCached(b *testing.B) {
 	doBenchmarkPartial(b, func(ns *partials.Namespace) error {
-		_, err := ns.IncludeCached("bench1", nil)
+		_, err := ns.IncludeCached(context.Background(), "bench1", nil)
 		return err
 	})
 }