config: Clone language map entries before modifying them

Now, with YAML anchor and alias support, these can point to shared data,
which must not be modified in place.

Fixes #14072

common/hdebug/debug.go

@@ -0,0 +1,61 @@
+// Copyright 2025 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 hdebug
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/gohugoio/hugo/common/types"
+	"github.com/gohugoio/hugo/htesting"
+)
+
+// Printf is a debug print function that should be removed before committing code to the repository.
+func Printf(format string, args ...any) {
+	panicIfRealCI()
+	if len(args) == 1 && !strings.Contains(format, "%") {
+		format = format + ": %v"
+	}
+	if !strings.HasSuffix(format, "\n") {
+		format = format + "\n"
+	}
+	fmt.Printf(format, args...)
+}
+
+func AssertNotNil(a ...any) {
+	panicIfRealCI()
+	for _, v := range a {
+		if types.IsNil(v) {
+			panic("hdebug.AssertNotNil: value is nil")
+		}
+	}
+}
+
+func Panicf(format string, args ...any) {
+	panicIfRealCI()
+	// fmt.Println(stack())
+	if len(args) == 1 && !strings.Contains(format, "%") {
+		format = format + ": %v"
+	}
+	if !strings.HasSuffix(format, "\n") {
+		format = format + "\n"
+	}
+	panic(fmt.Sprintf(format, args...))
+}
+
+func panicIfRealCI() {
+	if htesting.IsRealCI() {
+		panic("This debug statement should be removed before committing code!")
+	}
+}

common/maps/params.go

@@ -16,7 +16,6 @@ package maps
 import (
 	"errors"
 	"fmt"
-	xmaps "maps"
 	"strings"
 
 	"github.com/spf13/cast"
@@ -42,6 +41,14 @@ func (p Params) GetNested(indices ...string) any {
 // SetParams overwrites values in dst with values in src for common or new keys.
 // This is done recursively.
 func SetParams(dst, src Params) {
+	setParams(dst, src, 0)
+}
+
+func setParams(dst, src Params, depth int) {
+	const maxDepth = 1000
+	if depth > maxDepth {
+		panic(errors.New("max depth exceeded"))
+	}
 	for k, v := range src {
 		vv, found := dst[k]
 		if !found {
@@ -50,7 +57,7 @@ func SetParams(dst, src Params) {
 			switch vvv := vv.(type) {
 			case Params:
 				if pv, ok := v.(Params); ok {
-					SetParams(vvv, pv)
+					setParams(vvv, pv, depth+1)
 				} else {
 					dst[k] = v
 				}
@@ -116,9 +123,6 @@ func (p Params) merge(ps ParamsMergeStrategy, pp Params) {
 				}
 			}
 		} else if !noUpdate {
-			if vvv, ok := v.(Params); ok {
-				v = xmaps.Clone(vvv)
-			}
 			p[k] = v
 		}
 
@@ -356,6 +360,29 @@ func PrepareParams(m Params) {
 	}
 }
 
+// CloneParamsDeep does a deep clone of the given Params,
+// meaning that any nested Params will be cloned as well.
+func CloneParamsDeep(m Params) Params {
+	return cloneParamsDeep(m, 0)
+}
+
+func cloneParamsDeep(m Params, depth int) Params {
+	const maxDepth = 1000
+	if depth > maxDepth {
+		panic(errors.New("max depth exceeded"))
+	}
+	m2 := make(Params)
+	for k, v := range m {
+		switch vv := v.(type) {
+		case Params:
+			m2[k] = cloneParamsDeep(vv, depth+1)
+		default:
+			m2[k] = v
+		}
+	}
+	return m2
+}
+
 // PrepareParamsClone is like PrepareParams, but it does not modify the input.
 func PrepareParamsClone(m Params) Params {
 	m2 := make(Params)