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 #5068

tpl/tplimpl/template_ast_transformers.go

@@ -24,15 +24,14 @@ import (
 // decl keeps track of the variable mappings, i.e. $mysite => .Site etc.
 type decl map[string]string
 
-var paramsPaths = [][]string{
-	{"Params"},
-	{"Site", "Params"},
+const (
+	paramsIdentifier = "Params"
+)
 
-	// Site and Pag referenced from shortcodes
-	{"Page", "Site", "Params"},
-	{"Page", "Params"},
-
-	{"Site", "Language", "Params"},
+// Containers that may contain Params that we will not touch.
+var reservedContainers = map[string]bool{
+	// Aka .Site.Data.Params which must stay case sensitive.
+	"Data": true,
 }
 
 type templateContext struct {
@@ -155,6 +154,7 @@ 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,
@@ -167,31 +167,101 @@ func (d decl) indexOfReplacementStart(idents []string) int {
 		return -1
 	}
 
-	first := idents[0]
-	firstIsVar := first[0] == '$'
-
-	if l == 1 && !firstIsVar {
-		// This can not be a Params.x
-		return -1
-	}
-
-	if !firstIsVar {
-		found := false
-		for _, paramsPath := range paramsPaths {
-			if first == paramsPath[0] {
-				found = true
-				break
-			}
-		}
-		if !found {
+	if l == 1 {
+		first := idents[0]
+		if first == "" || first == paramsIdentifier || first[0] == '$' {
+			// This can not be a Params.x
 			return -1
 		}
 	}
 
+	var lookFurther bool
+	var needsVarExpansion bool
+	for _, ident := range idents {
+		if ident[0] == '$' {
+			lookFurther = true
+			needsVarExpansion = true
+			break
+		} else if ident == paramsIdentifier {
+			lookFurther = true
+			break
+		}
+	}
+
+	if !lookFurther {
+		return -1
+	}
+
+	var resolvedIdents []string
+
+	if !needsVarExpansion {
+		resolvedIdents = idents
+	} else {
+		var ok bool
+		resolvedIdents, ok = d.resolveVariables(idents)
+		if !ok {
+			return -1
+		}
+	}
+
+	var paramFound bool
+	for i, ident := range resolvedIdents {
+		if ident == paramsIdentifier {
+			if i > 0 {
+				container := resolvedIdents[i-1]
+				if reservedContainers[container] {
+					// .Data.Params.someKey
+					return -1
+				}
+				if !d.isKeyword(container) {
+					// where $pages ".Params.toc_hide" "!=" true
+					return -1
+				}
+			}
+			if i < len(resolvedIdents)-1 {
+				next := resolvedIdents[i+1]
+				if !d.isKeyword(next) {
+					return -1
+				}
+			}
+
+			paramFound = true
+			break
+		}
+	}
+
+	if !paramFound {
+		return -1
+	}
+
+	var paramSeen bool
+	idx := -1
+	for i, ident := range idents {
+		if ident == "" || ident[0] == '$' {
+			continue
+		}
+
+		if ident == paramsIdentifier {
+			paramSeen = true
+			idx = -1
+
+		} else {
+			if paramSeen {
+				return i
+			}
+			if idx == -1 {
+				idx = i
+			}
+		}
+	}
+	return idx
+
+}
+
+func (d decl) resolveVariables(idents []string) ([]string, bool) {
 	var (
-		resolvedIdents []string
-		replacements   []string
-		replaced       []string
+		replacements []string
+		replaced     []string
 	)
 
 	// An Ident can start out as one of
@@ -206,7 +276,7 @@ func (d decl) indexOfReplacementStart(idents []string) int {
 
 		if i > 20 {
 			// bail out
-			return -1
+			return nil, false
 		}
 
 		potentialVar := replacements[i]
@@ -225,7 +295,7 @@ func (d decl) indexOfReplacementStart(idents []string) int {
 
 		if !ok {
 			// Temporary range vars. We do not care about those.
-			return -1
+			return nil, false
 		}
 
 		replacement = strings.TrimPrefix(replacement, ".")
@@ -242,52 +312,10 @@ func (d decl) indexOfReplacementStart(idents []string) int {
 		}
 	}
 
-	resolvedIdents = append(replaced, idents[1:]...)
-
-	for _, paramPath := range paramsPaths {
-		if index := indexOfFirstRealIdentAfterWords(resolvedIdents, idents, paramPath...); index != -1 {
-			return index
-		}
-	}
-
-	return -1
+	return append(replaced, idents[1:]...), true
 
 }
 
-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
+func (d decl) isKeyword(s string) bool {
+	return !strings.ContainsAny(s, " -\"")
 }