Fix case issues with Params

There are currently several Params and case related issues floating around in Hugo.

This is very confusing for users and one of the most common support questions on the forum.

And while there have been done some great leg work in Viper etc., this is of limited value since this and similar doesn't work:

`Params.myCamelCasedParam`

Hugo has control over all the template method invocations, and can take care of all the lower-casing of the map lookup keys.

But that doesn't help with direct template lookups of type `Site.Params.TWITTER_CONFIG.USER_ID`.

This commit solves that by doing some carefully crafted modifications of the templates' AST -- lowercasing the params keys.

This is low-level work, but it's not like the template API wil change -- and this is important enough to defend such "bit fiddling".

Tests are added for all the template engines: Go templates, Ace and Amber.

Fixes #2615
Fixes #1129
Fixes #2590

.gitignore

@@ -11,3 +11,4 @@ cover.out
 .DS_Store
 *~
 vendor/*/
+*.bench

hugolib/case_insensitive_test.go

@@ -0,0 +1,289 @@
+// Copyright 2016 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 hugolib
+
+import (
+	"fmt"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+var (
+	caseMixingSiteConfigTOML = `
+Title = "In an Insensitive Mood"
+DefaultContentLanguage = "nn"
+defaultContentLanguageInSubdir = true
+
+[Blackfriday]
+AngledQuotes = true
+HrefTargetBlank = true
+
+[Params]
+Search = true
+Color = "green"
+mood = "Happy"
+[Params.Colors]
+Blue = "blue"
+Yellow = "yellow"
+
+[Languages]
+[Languages.nn]
+title = "Nynorsk title"
+languageName = "Nynorsk"
+weight = 1
+
+[Languages.en]
+TITLE = "English title"
+LanguageName = "English"
+Mood = "Thoughtful"
+Weight = 2
+COLOR = "Pink"
+[Languages.en.blackfriday]
+angledQuotes = false
+hrefTargetBlank = false
+[Languages.en.Colors]
+BLUE = "blues"
+yellow = "golden"
+`
+	caseMixingPage1En = `
+---
+TITLE: Page1 En Translation
+BlackFriday:
+  AngledQuotes: false
+Color: "black"
+Search: true
+mooD: "sad and lonely"
+ColorS: 
+  Blue: "bluesy"
+  Yellow: "sunny"  
+---
+# "Hi"
+{{< shortcode >}}
+`
+
+	caseMixingPage1 = `
+---
+titLe: Side 1
+blackFriday:
+  angledQuotes: true
+color: "red"
+search: false
+MooD: "sad"
+COLORS: 
+  blue: "heavenly"
+  yelloW: "Sunny"  
+---
+# "Hi"
+{{< shortcode >}}
+`
+
+	caseMixingPage2 = `
+---
+TITLE: Page2 Title
+BlackFriday:
+  AngledQuotes: false
+Color: "black"
+search: true
+MooD: "moody"
+ColorS: 
+  Blue: "sky"
+  YELLOW: "flower"  
+---
+# Hi
+{{< shortcode >}}
+`
+)
+
+func caseMixingTestsWriteCommonSources(t *testing.T) {
+	writeSource(t, filepath.Join("content", "sect1", "page1.md"), caseMixingPage1)
+	writeSource(t, filepath.Join("content", "sect2", "page2.md"), caseMixingPage2)
+	writeSource(t, filepath.Join("content", "sect1", "page1.en.md"), caseMixingPage1En)
+
+	writeSource(t, "layouts/shortcodes/shortcode.html", `
+Shortcode Page: {{ .Page.Params.COLOR }}|{{ .Page.Params.Colors.Blue  }}
+Shortcode Site: {{ .Page.Site.Params.COLOR }}|{{ .Site.Params.COLORS.YELLOW  }}
+`)
+
+	writeSource(t, "layouts/partials/partial.html", `
+Partial Page: {{ .Params.COLOR }}|{{ .Params.Colors.Blue }}
+Partial Site: {{ .Site.Params.COLOR }}|{{ .Site.Params.COLORS.YELLOW }}
+`)
+
+	writeSource(t, "config.toml", caseMixingSiteConfigTOML)
+
+}
+
+func TestCaseInsensitiveConfigurationVariations(t *testing.T) {
+	// See issues 2615, 1129, 2590 and maybe some others
+	// Also see 2598
+	//
+	// Viper is now, at least for the Hugo part, case insensitive
+	// So we need tests for all of it, with needed adjustments on the Hugo side.
+	// Not sure what that will be. Let us see.
+
+	// So all the below with case variations:
+	// config: regular fields, blackfriday config, param with nested map
+	// language: new and overridden values, in regular fields and nested paramsmap
+	// page frontmatter: regular fields, blackfriday config, param with nested map
+
+	testCommonResetState()
+	caseMixingTestsWriteCommonSources(t)
+
+	writeSource(t, filepath.Join("layouts", "_default", "baseof.html"), `
+Block Page Colors: {{ .Params.COLOR }}|{{ .Params.Colors.Blue }}	
+{{ block "main" . }}default{{end}}`)
+
+	writeSource(t, filepath.Join("layouts", "sect2", "single.html"), `
+{{ define "main"}}
+Page Colors: {{ .Params.CoLOR }}|{{ .Params.Colors.Blue }}
+Site Colors: {{ .Site.Params.COlOR }}|{{ .Site.Params.COLORS.YELLOW }}
+{{ .Content }}
+{{ partial "partial.html" . }}
+{{ end }}
+`)
+
+	writeSource(t, filepath.Join("layouts", "_default", "single.html"), `
+Page Title: {{ .Title }}
+Site Title: {{ .Site.Title }}
+Site Lang Mood: {{ .Site.Language.Params.MOoD }}
+Page Colors: {{ .Params.COLOR }}|{{ .Params.Colors.Blue }}
+Site Colors: {{ .Site.Params.COLOR }}|{{ .Site.Params.COLORS.YELLOW }}
+{{ .Content }}
+{{ partial "partial.html" . }}
+`)
+
+	if err := LoadGlobalConfig("", "config.toml"); err != nil {
+		t.Fatalf("Failed to load config: %s", err)
+	}
+
+	sites, err := NewHugoSitesFromConfiguration()
+
+	if err != nil {
+		t.Fatalf("Failed to create sites: %s", err)
+	}
+
+	err = sites.Build(BuildCfg{})
+
+	if err != nil {
+		t.Fatalf("Failed to build sites: %s", err)
+	}
+
+	assertFileContent(t, filepath.Join("public", "nn", "sect1", "page1", "index.html"), true,
+		"Page Colors: red|heavenly",
+		"Site Colors: green|yellow",
+		"Site Lang Mood: Happy",
+		"Shortcode Page: red|heavenly",
+		"Shortcode Site: green|yellow",
+		"Partial Page: red|heavenly",
+		"Partial Site: green|yellow",
+		"Page Title: Side 1",
+		"Site Title: Nynorsk title",
+		"&laquo;Hi&raquo;", // angled quotes
+	)
+
+	assertFileContent(t, filepath.Join("public", "en", "sect1", "page1", "index.html"), true,
+		"Site Colors: Pink|golden",
+		"Page Colors: black|bluesy",
+		"Site Lang Mood: Thoughtful",
+		"Page Title: Page1 En Translation",
+		"Site Title: English title",
+		"&ldquo;Hi&rdquo;",
+	)
+
+	assertFileContent(t, filepath.Join("public", "nn", "sect2", "page2", "index.html"), true,
+		"Page Colors: black|sky",
+		"Site Colors: green|yellow",
+		"Shortcode Page: black|sky",
+		"Block Page Colors: black|sky",
+		"Partial Page: black|sky",
+		"Partial Site: green|yellow",
+	)
+}
+
+func TestCaseInsensitiveConfigurationForAllTemplateEngines(t *testing.T) {
+	noOp := func(s string) string {
+		return s
+	}
+
+	amberFixer := func(s string) string {
+		fixed := strings.Replace(s, "{{ .Site.Params", "{{ Site.Params", -1)
+		fixed = strings.Replace(fixed, "{{ .Params", "{{ Params", -1)
+		fixed = strings.Replace(fixed, ".Content", "Content", -1)
+		fixed = strings.Replace(fixed, "{{", "#{", -1)
+		fixed = strings.Replace(fixed, "}}", "}", -1)
+
+		return fixed
+	}
+
+	for _, config := range []struct {
+		suffix        string
+		templateFixer func(s string) string
+	}{
+		{"amber", amberFixer},
+		{"html", noOp},
+		{"ace", noOp},
+	} {
+		doTestCaseInsensitiveConfigurationForTemplateEngine(t, config.suffix, config.templateFixer)
+
+	}
+
+}
+
+func doTestCaseInsensitiveConfigurationForTemplateEngine(t *testing.T, suffix string, templateFixer func(s string) string) {
+
+	testCommonResetState()
+	caseMixingTestsWriteCommonSources(t)
+
+	t.Log("Testing", suffix)
+
+	templTemplate := `
+p
+	|
+	| Page Colors: {{ .Params.CoLOR }}|{{ .Params.Colors.Blue }}
+	| Site Colors: {{ .Site.Params.COlOR }}|{{ .Site.Params.COLORS.YELLOW }}
+	| {{ .Content }}
+
+`
+
+	templ := templateFixer(templTemplate)
+
+	t.Log(templ)
+
+	writeSource(t, filepath.Join("layouts", "_default", fmt.Sprintf("single.%s", suffix)), templ)
+
+	if err := LoadGlobalConfig("", "config.toml"); err != nil {
+		t.Fatalf("Failed to load config: %s", err)
+	}
+
+	sites, err := NewHugoSitesFromConfiguration()
+
+	if err != nil {
+		t.Fatalf("Failed to create sites: %s", err)
+	}
+
+	err = sites.Build(BuildCfg{})
+
+	if err != nil {
+		t.Fatalf("Failed to build sites: %s", err)
+	}
+
+	assertFileContent(t, filepath.Join("public", "nn", "sect1", "page1", "index.html"), true,
+		"Page Colors: red|heavenly",
+		"Site Colors: green|yellow",
+		"Shortcode Page: red|heavenly",
+		"Shortcode Site: green|yellow",
+	)
+
+}

hugolib/page.go

@@ -901,6 +901,9 @@ func (p *Page) update(f interface{}) error {
 		return fmt.Errorf("no metadata found")
 	}
 	m := f.(map[string]interface{})
+	// Needed for case insensitive fetching of params values
+	helpers.ToLowerMap(m)
+
 	var err error
 	var draft, published, isCJKLanguage *bool
 	for k, v := range m {

hugolib/site.go

@@ -1805,7 +1805,7 @@ func (s *Site) renderForLayouts(name string, d interface{}, w io.Writer, layouts
 	if err := s.renderThing(d, layout, w); err != nil {
 
 		// Behavior here should be dependent on if running in server or watch mode.
-		distinctErrorLogger.Printf("Error while rendering %s: %v", name, err)
+		distinctErrorLogger.Printf("Error while rendering %s: %.60s…", name, err)
 		if !s.running() && !testMode {
 			// TODO(bep) check if this can be propagated
 			os.Exit(-1)

hugolib/site_render.go

@@ -58,7 +58,7 @@ func (s *Site) renderPages() error {
 
 	err := <-errs
 	if err != nil {
-		return fmt.Errorf("Error(s) rendering pages: %s", err)
+		return fmt.Errorf("Error(s) rendering pages: %.60s…", err)
 	}
 	return nil
 }

tpl/template.go

@@ -213,11 +213,16 @@ func (t *GoHTMLTemplate) AddInternalShortcode(name, content string) error {
 
 func (t *GoHTMLTemplate) AddTemplate(name, tpl string) error {
 	t.checkState()
-	_, err := t.New(name).Parse(tpl)
+	templ, err := t.New(name).Parse(tpl)
 	if err != nil {
 		t.errors = append(t.errors, &templateErr{name: name, err: err})
+		return err
 	}
-	return err
+	if err := applyTemplateTransformers(templ); err != nil {
+		return err
+	}
+
+	return nil
 }
 
 func (t *GoHTMLTemplate) AddTemplateFileWithMaster(name, overlayFilename, masterFilename string) error {
@@ -264,7 +269,11 @@ func (t *GoHTMLTemplate) AddTemplateFileWithMaster(name, overlayFilename, master
 		// The extra lookup is a workaround, see
 		// * https://github.com/golang/go/issues/16101
 		// * https://github.com/spf13/hugo/issues/2549
-		t.overlays[name] = overlayTpl.Lookup(overlayTpl.Name())
+		overlayTpl = overlayTpl.Lookup(overlayTpl.Name())
+		if err := applyTemplateTransformers(overlayTpl); err != nil {
+			return err
+		}
+		t.overlays[name] = overlayTpl
 	}
 
 	return err
@@ -291,11 +300,12 @@ func (t *GoHTMLTemplate) AddAceTemplate(name, basePath, innerPath string, baseCo
 		t.errors = append(t.errors, &templateErr{name: name, err: err})
 		return err
 	}
-	_, err = ace.CompileResultWithTemplate(t.New(name), parsed, nil)
+	templ, err := ace.CompileResultWithTemplate(t.New(name), parsed, nil)
 	if err != nil {
 		t.errors = append(t.errors, &templateErr{name: name, err: err})
+		return err
 	}
-	return err
+	return applyTemplateTransformers(templ)
 }
 
 func (t *GoHTMLTemplate) AddTemplateFile(name, baseTemplatePath, path string) error {
@@ -317,9 +327,12 @@ func (t *GoHTMLTemplate) AddTemplateFile(name, baseTemplatePath, path string) er
 			return err
 		}
 
-		if _, err := compiler.CompileWithTemplate(t.New(templateName)); err != nil {
+		templ, err := compiler.CompileWithTemplate(t.New(templateName))
+		if err != nil {
 			return err
 		}
+
+		return applyTemplateTransformers(templ)
 	case ".ace":
 		var innerContent, baseContent []byte
 		innerContent, err := afero.ReadFile(hugofs.Source(), path)
@@ -353,8 +366,6 @@ func (t *GoHTMLTemplate) AddTemplateFile(name, baseTemplatePath, path string) er
 		return t.AddTemplate(name, string(b))
 	}
 
-	return nil
-
 }
 
 func (t *GoHTMLTemplate) GenerateTemplateNameFrom(base, path string) string {
@@ -467,7 +478,7 @@ func (t *GoHTMLTemplate) loadTemplates(absPath string, prefix string) {
 			}
 
 			if err := t.AddTemplateFile(tplName, baseTemplatePath, path); err != nil {
-				jww.ERROR.Printf("Failed to add template %s: %s", tplName, err)
+				jww.ERROR.Printf("Failed to add template %s in path %s: %s", tplName, path, err)
 			}
 
 		}

tpl/template_ast_transformers.go

@@ -0,0 +1,256 @@
+// Copyright 2016 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 tpl
+
+import (
+	"errors"
+	"html/template"
+	"strings"
+	"text/template/parse"
+)
+
+// decl keeps track of the variable mappings, i.e. $mysite => .Site etc.
+type decl map[string]string
+
+var paramsPaths = [][]string{
+	{"Params"},
+	{"Site", "Params"},
+
+	// Site and Pag referenced from shortcodes
+	{"Page", "Site", "Params"},
+	{"Page", "Params"},
+
+	{"Site", "Language", "Params"},
+}
+
+type templateContext struct {
+	decl  decl
+	templ *template.Template
+}
+
+func newTemplateContext(templ *template.Template) *templateContext {
+	return &templateContext{templ: templ, decl: make(map[string]string)}
+
+}
+
+func applyTemplateTransformers(templ *template.Template) error {
+	if templ == nil || templ.Tree == nil {
+		return errors.New("expected template, but none provided")
+	}
+
+	c := newTemplateContext(templ)
+
+	c.paramsKeysToLower(templ.Tree.Root)
+
+	return nil
+}
+
+// paramsKeysToLower is made purposely non-generic to make it not so tempting
+// to do more of these hard-to-maintain AST transformations.
+func (c *templateContext) paramsKeysToLower(n parse.Node) {
+
+	switch x := n.(type) {
+	case *parse.ListNode:
+		if x != nil {
+			c.paramsKeysToLowerForNodes(x.Nodes...)
+		}
+	case *parse.ActionNode:
+		c.paramsKeysToLowerForNodes(x.Pipe)
+	case *parse.IfNode:
+		c.paramsKeysToLowerForNodes(x.Pipe, x.List, x.ElseList)
+	case *parse.WithNode:
+		c.paramsKeysToLowerForNodes(x.Pipe, x.List, x.ElseList)
+	case *parse.RangeNode:
+		c.paramsKeysToLowerForNodes(x.Pipe, x.List, x.ElseList)
+	case *parse.TemplateNode:
+		subTempl := c.templ.Lookup(x.Name)
+		if subTempl != nil {
+			c.paramsKeysToLowerForNodes(subTempl.Tree.Root)
+		}
+	case *parse.PipeNode:
+		for i, elem := range x.Decl {
+			if len(x.Cmds) > i {
+				// maps $site => .Site etc.
+				c.decl[elem.Ident[0]] = x.Cmds[i].String()
+			}
+		}
+
+		for _, cmd := range x.Cmds {
+			c.paramsKeysToLower(cmd)
+		}
+
+	case *parse.CommandNode:
+		for _, elem := range x.Args {
+			switch an := elem.(type) {
+			case *parse.FieldNode:
+				c.updateIdentsIfNeeded(an.Ident)
+			case *parse.VariableNode:
+				c.updateIdentsIfNeeded(an.Ident)
+			}
+		}
+	}
+}
+
+func (c *templateContext) paramsKeysToLowerForNodes(nodes ...parse.Node) {
+	for _, node := range nodes {
+		c.paramsKeysToLower(node)
+	}
+}
+
+func (c *templateContext) updateIdentsIfNeeded(idents []string) {
+	index := c.decl.indexOfReplacementStart(idents)
+
+	if index == -1 {
+		return
+	}
+
+	for i := index; i < len(idents); i++ {
+		idents[i] = strings.ToLower(idents[i])
+	}
+}
+
+// indexOfReplacementStart will return the index of where to start doing replacement,
+// -1 if none needed.
+func (d decl) indexOfReplacementStart(idents []string) int {
+
+	l := len(idents)
+
+	if l == 0 {
+		return -1
+	}
+
+	first := idents[0]
+	firstIsVar := first[0] == '$'
+
+	if l == 1 && !firstIsVar {
+		// This can not be a Params.x
+		return -1
+	}
+
+	if !firstIsVar {
+		found := false
+		for _, paramsPath := range paramsPaths {
+			if first == paramsPath[0] {
+				found = true
+				break
+			}
+		}
+		if !found {
+			return -1
+		}
+	}
+
+	var (
+		resolvedIdents []string
+		replacements   []string
+		replaced       []string
+	)
+
+	// An Ident can start out as one of
+	// [Params] [$blue] [$colors.Blue]
+	// We need to resolve the variables, so
+	// $blue => [Params Colors Blue]
+	// etc.
+	replacements = []string{idents[0]}
+
+	// Loop until there are no more $vars to resolve.
+	for i := 0; i < len(replacements); i++ {
+
+		if i > 20 {
+			// bail out
+			return -1
+		}
+
+		potentialVar := replacements[i]
+
+		if potentialVar == "$" {
+			continue
+		}
+
+		if potentialVar == "" || potentialVar[0] != '$' {
+			// leave it as is
+			replaced = append(replaced, strings.Split(potentialVar, ".")...)
+			continue
+		}
+
+		replacement, ok := d[potentialVar]
+
+		if !ok {
+			// Temporary range vars. We do not care about those.
+			return -1
+		}
+
+		replacement = strings.TrimPrefix(replacement, ".")
+
+		if replacement == "" {
+			continue
+		}
+
+		if replacement[0] == '$' {
+			// Needs further expansion
+			replacements = append(replacements, strings.Split(replacement, ".")...)
+		} else {
+			replaced = append(replaced, strings.Split(replacement, ".")...)
+		}
+	}
+
+	resolvedIdents = append(replaced, idents[1:]...)
+
+	for _, paramPath := range paramsPaths {
+		if index := indexOfFirstRealIdentAfterWords(resolvedIdents, idents, paramPath...); index != -1 {
+			return index
+		}
+	}
+
+	return -1
+
+}
+
+func indexOfFirstRealIdentAfterWords(resolvedIdents, idents []string, words ...string) int {
+	if !sliceStartsWith(resolvedIdents, words...) {
+		return -1
+	}
+
+	for i, ident := range idents {
+		if ident == "" || ident[0] == '$' {
+			continue
+		}
+		found := true
+		for _, word := range words {
+			if ident == word {
+				found = false
+				break
+			}
+		}
+		if found {
+			return i
+		}
+	}
+
+	return -1
+}
+
+func sliceStartsWith(slice []string, words ...string) bool {
+
+	if len(slice) < len(words) {
+		return false
+	}
+
+	for i, word := range words {
+		if word != slice[i] {
+			return false
+		}
+	}
+	return true
+}

tpl/template_ast_transformers_test.go

@@ -0,0 +1,259 @@
+// Copyright 2016 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 tpl
+
+import (
+	"bytes"
+	"testing"
+
+	"html/template"
+
+	jww "github.com/spf13/jwalterweatherman"
+	"github.com/stretchr/testify/require"
+)
+
+var (
+	testFuncs = map[string]interface{}{
+		"Echo": func(v interface{}) interface{} { return v },
+	}
+
+	paramsData = map[string]interface{}{
+		"NotParam": "Hi There",
+		"Slice":    []int{1, 3},
+		"Params": map[string]interface{}{
+			"lower": "P1L",
+		},
+		"Site": map[string]interface{}{
+			"Params": map[string]interface{}{
+				"lower": "P2L",
+				"slice": []int{1, 3},
+			},
+			"Language": map[string]interface{}{
+				"Params": map[string]interface{}{
+					"lower": "P22L",
+				},
+			},
+			"Data": map[string]interface{}{
+				"Params": map[string]interface{}{
+					"NOLOW": "P3H",
+				},
+			},
+		},
+	}
+
+	paramsTempl = `
+{{ $page := . }}
+{{ $pageParams := .Params }}
+{{ $site := .Site }}
+{{ $siteParams := .Site.Params }}
+{{ $data := .Site.Data }}
+{{ $notparam := .NotParam }}
+
+P1: {{ .Params.LOWER }}
+P1_2: {{ $.Params.LOWER }}
+P1_3: {{ $page.Params.LOWER }}
+P1_4: {{ $pageParams.LOWER }}
+P2: {{ .Site.Params.LOWER }}
+P2_2: {{ $.Site.Params.LOWER }}
+P2_3: {{ $site.Params.LOWER }}
+P2_4: {{ $siteParams.LOWER }}
+P22: {{ .Site.Language.Params.LOWER }}
+P3: {{ .Site.Data.Params.NOLOW }}
+P3_2: {{ $.Site.Data.Params.NOLOW }}
+P3_3: {{ $site.Data.Params.NOLOW }}
+P3_4: {{ $data.Params.NOLOW }}
+P4: {{ range $i, $e := .Site.Params.SLICE }}{{ $e }}{{ end }}
+P5: {{ Echo .Params.LOWER }}
+P5_2: {{ Echo $site.Params.LOWER }}
+{{ if .Params.LOWER }}
+IF: {{ .Params.LOWER }}
+{{ end }}
+{{ if .Params.NOT_EXIST }}
+{{ else }}
+ELSE: {{ .Params.LOWER }}
+{{ end }}
+
+
+{{ with .Params.LOWER }}
+WITH: {{ . }}
+{{ end }}
+
+
+{{ range .Slice }}
+RANGE: {{ . }}: {{ $.Params.LOWER }}
+{{ end }}
+{{ index .Slice 1 }}
+{{ .NotParam }}
+{{ .NotParam }}
+{{ .NotParam }}
+{{ .NotParam }}
+{{ .NotParam }}
+{{ .NotParam }}
+{{ .NotParam }}
+{{ .NotParam }}
+{{ .NotParam }}
+{{ .NotParam }}
+{{ $notparam }}
+`
+)
+
+func TestParamsKeysToLower(t *testing.T) {
+
+	require.Error(t, applyTemplateTransformers(nil))
+
+	templ, err := template.New("foo").Funcs(testFuncs).Parse(paramsTempl)
+
+	require.NoError(t, err)
+
+	c := newTemplateContext(templ)
+
+	require.Equal(t, -1, c.decl.indexOfReplacementStart([]string{}))
+
+	c.paramsKeysToLower(templ.Tree.Root)
+
+	var b bytes.Buffer
+
+	require.NoError(t, templ.Execute(&b, paramsData))
+
+	result := b.String()
+
+	require.Contains(t, result, "P1: P1L")
+	require.Contains(t, result, "P1_2: P1L")
+	require.Contains(t, result, "P1_3: P1L")
+	require.Contains(t, result, "P1_4: P1L")
+	require.Contains(t, result, "P2: P2L")
+	require.Contains(t, result, "P2_2: P2L")
+	require.Contains(t, result, "P2_3: P2L")
+	require.Contains(t, result, "P2_4: P2L")
+	require.Contains(t, result, "P22: P22L")
+	require.Contains(t, result, "P3: P3H")
+	require.Contains(t, result, "P3_2: P3H")
+	require.Contains(t, result, "P3_3: P3H")
+	require.Contains(t, result, "P3_4: P3H")
+	require.Contains(t, result, "P4: 13")
+	require.Contains(t, result, "P5: P1L")
+	require.Contains(t, result, "P5_2: P2L")
+
+	require.Contains(t, result, "IF: P1L")
+	require.Contains(t, result, "ELSE: P1L")
+
+	require.Contains(t, result, "WITH: P1L")
+
+	require.Contains(t, result, "RANGE: 3: P1L")
+
+	require.Contains(t, result, "Hi There")
+}
+
+func BenchmarkTemplateParamsKeysToLower(b *testing.B) {
+	templ, err := template.New("foo").Funcs(testFuncs).Parse(paramsTempl)
+
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	templates := make([]*template.Template, b.N)
+
+	for i := 0; i < b.N; i++ {
+		templates[i], err = templ.Clone()
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		c := newTemplateContext(templates[i])
+		c.paramsKeysToLower(templ.Tree.Root)
+	}
+}
+
+func TestParamsKeysToLowerVars(t *testing.T) {
+	var (
+		ctx = map[string]interface{}{
+			"Params": map[string]interface{}{
+				"colors": map[string]interface{}{
+					"blue": "Amber",
+				},
+			},
+		}
+
+		// This is how Amber behaves:
+		paramsTempl = `
+{{$__amber_1 := .Params.Colors}}
+{{$__amber_2 := $__amber_1.Blue}}
+Color: {{$__amber_2}}
+Blue: {{ $__amber_1.Blue}}
+`
+	)
+
+	templ, err := template.New("foo").Parse(paramsTempl)
+
+	require.NoError(t, err)
+
+	c := newTemplateContext(templ)
+
+	c.paramsKeysToLower(templ.Tree.Root)
+
+	var b bytes.Buffer
+
+	require.NoError(t, templ.Execute(&b, ctx))
+
+	result := b.String()
+
+	require.Contains(t, result, "Color: Amber")
+
+}
+
+func TestParamsKeysToLowerInBlockTemplate(t *testing.T) {
+
+	var (
+		ctx = map[string]interface{}{
+			"Params": map[string]interface{}{
+				"lower": "P1L",
+			},
+		}
+
+		master = `
+P1: {{ .Params.LOWER }}
+{{ block "main" . }}DEFAULT{{ end }}`
+		overlay = `
+{{ define "main" }}
+P2: {{ .Params.LOWER }}
+{{ end }}`
+	)
+
+	masterTpl, err := template.New("foo").Parse(master)
+	require.NoError(t, err)
+
+	overlayTpl, err := template.Must(masterTpl.Clone()).Parse(overlay)
+	require.NoError(t, err)
+	overlayTpl = overlayTpl.Lookup(overlayTpl.Name())
+
+	c := newTemplateContext(overlayTpl)
+
+	c.paramsKeysToLower(overlayTpl.Tree.Root)
+
+	var b bytes.Buffer
+
+	require.NoError(t, overlayTpl.Execute(&b, ctx))
+
+	result := b.String()
+
+	require.Contains(t, result, "P1: P1L")
+	require.Contains(t, result, "P2: P1L")
+}
+
+func init() {
+	jww.SetStdoutThreshold(jww.LevelCritical)
+}