Fix "assignment to entry in nil map" on empty YAML config files

Fixes #14074

Author: bep

common/herrors/errors.go

@@ -17,22 +17,13 @@ package herrors
 import (
 	"errors"
 	"fmt"
-	"io"
 	"os"
 	"regexp"
-	"runtime"
 	"runtime/debug"
 	"strings"
 	"time"
 )
 
-// PrintStackTrace prints the current stacktrace to w.
-func PrintStackTrace(w io.Writer) {
-	buf := make([]byte, 1<<16)
-	runtime.Stack(buf, true)
-	fmt.Fprintf(w, "%s", buf)
-}
-
 // ErrorSender is a, typically, non-blocking error handler.
 type ErrorSender interface {
 	SendError(err error)

config/allconfig/load.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"runtime/debug"
 	"strings"
 
 	"github.com/gobwas/glob"
@@ -44,6 +45,7 @@ func LoadConfig(d ConfigSourceDescriptor) (configs *Configs, err error) {
 	defer func() {
 		if r := recover(); r != nil {
 			err = fmt.Errorf("failed to load config: %v", r)
+			debug.PrintStack()
 		}
 	}()
 

hugolib/config_test.go

@@ -1649,3 +1649,16 @@ Params: {{ site.Params }}|
 
 	}
 }
+
+func TestConfigYAMLNilMapIssue14074(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- config/_default/taxonomies.yaml --
+# empty on purpose
+-- hugo.yaml --
+
+`
+
+	Test(t, files)
+}

parser/metadecoders/decoder.go

@@ -86,6 +86,15 @@ func (d Decoder) UnmarshalToMap(data []byte, f Format) (map[string]any, error) {
 
 	err := d.UnmarshalTo(data, f, &m)
 
+	if m == nil {
+		// We migrated to github.com/goccy/go-yaml in v0.152.0,
+		// which produces nil maps for empty YAML files (and empty map nodes), unlike gopkg.in/yaml.v2.
+		//
+		// To prevent crashes when trying to handle empty config files etc., we ensure we always return a non-nil map here.
+		// See issue 14074.
+		m = make(map[string]any)
+	}
+
 	return m, err
 }
 

parser/metadecoders/decoder_integration_test.go

@@ -0,0 +1,43 @@
+// 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 metadecoders_test
+
+import (
+	"testing"
+
+	"github.com/gohugoio/hugo/hugolib"
+)
+
+func TestYAMLIntegerSortIssue14078(t *testing.T) {
+	files := `
+-- assets/mydata.yaml --
+a:
+   weight: 1
+x:
+  weight: 2
+c:
+  weight: 3
+t:
+  weight: 4
+
+-- layouts/all.html --
+{{ $mydata := resources.Get "mydata.yaml" | transform.Unmarshal }}
+Sorted: {{ sort $mydata "weight" }}|
+
+`
+
+	b := hugolib.Test(t, files)
+
+	b.AssertFileContent("public/index.html", "Sorted: [map[weight:1] map[weight:2] map[weight:3] map[weight:4]]|")
+}