tpl/tplimpl: Reimplement the ".Params tolower" template transformer

All `.Params` are stored lowercase, but it should work to access them `.Page.camelCase` etc. There was, however, some holes in the logic with the old transformer.

This commit fixes that by applying a blacklist instead of the old whitelist logic. `.Param` is a very distinct key. The original case will be kept in `.Data.Params.myParam`, but other than that it will be lowercased.

Fixes gohugoio#5068

tpl/tplimpl/template_ast_transformers.go

@@ -165,6 +165,7 @@ func (c *templateContext) updateIdentsIfNeeded(idents []string) {
 	for i := index; i < len(idents); i++ {
 		idents[i] = strings.ToLower(idents[i])
 	}
+
 }
 
 // indexOfReplacementStart will return the index of where to start doing replacement,
@@ -187,7 +188,7 @@ func (d decl) indexOfReplacementStart(idents []string) int {
 
 	var lookFurther bool
 	for _, ident := range idents {
-		if ident == "Params" || ident[0] == '$' {
+		if ident == paramsIdentifier || ident[0] == '$' {
 			lookFurther = true
 			break
 		}
@@ -256,15 +257,14 @@ func (d decl) indexOfReplacementStart(idents []string) int {
 	paramIdx := -1
 	for i, ident := range resolvedIdents {
 		if ident == paramsIdentifier {
-			if i == len(resolvedIdents)-2 {
-				if i > 0 {
-					container := resolvedIdents[i-1]
-					if reservedContainers[container] {
-						break
-					}
+			if i > 0 {
+				container := resolvedIdents[i-1]
+				if reservedContainers[container] {
+					break
 				}
-				paramIdx = i
 			}
+			paramIdx = i
+
 			break
 		}
 	}
@@ -273,44 +273,26 @@ func (d decl) indexOfReplacementStart(idents []string) int {
 		return -1
 	}
 
-	return len(idents) - 1
-
-}
-
-func indexOfFirstRealIdentAfterWords(resolvedIdents, idents []string, words ...string) int {
-	if !sliceStartsWith(resolvedIdents, words...) {
-		return -1
-	}
-
+	var paramSeen bool
+	idx := -1
 	for i, ident := range idents {
 		if ident == "" || ident[0] == '$' {
 			continue
 		}
-		found := true
-		for _, word := range words {
-			if ident == word {
-				found = false
-				break
+		if ident == paramsIdentifier {
+			paramSeen = true
+			idx = -1
+		} else {
+			if paramSeen {
+				return i
+			}
+			if idx == -1 {
+				idx = i
 			}
 		}
-		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
+	return idx
+
 }

tpl/tplimpl/template_ast_transformers_test.go

@@ -31,6 +31,7 @@ var (
 		"Slice":    []int{1, 3},
 		"Params": map[string]interface{}{
 			"lower": "P1L",
+			"slice": []int{1, 3},
 		},
 		"CurrentSection": map[string]interface{}{
 			"Params": map[string]interface{}{
@@ -115,6 +116,8 @@ RANGE: {{ . }}: {{ $.Params.LOWER }}
 F1: {{ printf "themes/%s-theme" .Site.Params.LOWER }}
 F2: {{ Echo (printf "themes/%s-theme" $lower) }}
 F3: {{ Echo (printf "themes/%s-theme" .Site.Params.LOWER) }}
+
+PSLICE: {{ range .Params.SLICE }}PSLICE{{.}}|{{ end }}
 `
 )
 
@@ -170,7 +173,9 @@ func TestParamsKeysToLower(t *testing.T) {
 	require.Contains(t, result, "F2: themes/P2L-theme")
 	require.Contains(t, result, "F3: themes/P2L-theme")
 
-	// Issue #5068 and similar
+	require.Contains(t, result, "PSLICE: PSLICE1|PSLICE3|")
+
+	// Issue #5068
 	require.Contains(t, result, "PCurrentSection: pcurrentsection")
 
 }
@@ -199,13 +204,16 @@ func BenchmarkTemplateParamsKeysToLower(b *testing.B) {
 	}
 }
 
-func TestParamsKeysToLowVars(t *testing.T) {
+func TestParamsKeysToLowerVars(t *testing.T) {
 	t.Parallel()
 	var (
 		ctx = map[string]interface{}{
 			"Params": map[string]interface{}{
 				"colors": map[string]interface{}{
 					"blue": "Amber",
+					"pretty": map[string]interface{}{
+						"first": "Indigo",
+					},
 				},
 			},
 		}
@@ -214,8 +222,14 @@ func TestParamsKeysToLowVars(t *testing.T) {
 		paramsTempl = `
 {{$__amber_1 := .Params.Colors}}
 {{$__amber_2 := $__amber_1.Blue}}
+{{$__amber_3 := $__amber_1.Pretty}}
+{{$__amber_4 := .Params}}
+
 Color: {{$__amber_2}}
 Blue: {{ $__amber_1.Blue}}
+Pretty First1: {{ $__amber_3.First}}
+Pretty First2: {{ $__amber_1.Pretty.First}}
+Pretty First3: {{ $__amber_4.COLORS.PRETTY.FIRST}}
 `
 	)
 
@@ -234,6 +248,10 @@ Blue: {{ $__amber_1.Blue}}
 	result := b.String()
 
 	require.Contains(t, result, "Color: Amber")
+	require.Contains(t, result, "Blue: Amber")
+	require.Contains(t, result, "Pretty First1: Indigo")
+	require.Contains(t, result, "Pretty First2: Indigo")
+	require.Contains(t, result, "Pretty First3: Indigo")
 
 }