Treat empty or all-comments yaml file as no-op when loading it

go/yamlutil/yamlutil.go

@@ -1,7 +1,9 @@
 package yamlutil
 
 import (
+	"errors"
 	"fmt"
+	"io"
 	"os"
 
 	"gopkg.in/yaml.v3"
@@ -10,14 +12,15 @@ import (
 // LoadYamlFile reads the file at the given path and unmarshals it into the
 // given pointer.
 func LoadYamlFile(into any, path string) error {
-
 	file, err := os.Open(path)
 	if err != nil {
 		return fmt.Errorf("opening file: %w", err)
 	}
 	defer file.Close()
 
-	if err = yaml.NewDecoder(file).Decode(into); err != nil {
+	if err = yaml.NewDecoder(file).Decode(into); errors.Is(err, io.EOF) {
+		return nil
+	} else if err != nil {
 		return fmt.Errorf("decoding yaml: %w", err)
 	}
 

go/yamlutil/yamlutil_test.go

@@ -0,0 +1,56 @@
+package yamlutil
+
+import (
+	"os"
+	"path/filepath"
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestLoadYamlFile(t *testing.T) {
+	type structA struct {
+		A int
+		B string
+	}
+
+	tests := []struct {
+		name string
+		body string
+		want any
+	}{
+		{
+			name: "empty body",
+			body: "",
+			want: structA{},
+		},
+		{
+			name: "all comments",
+			body: `# foo
+			# bar`,
+			want: structA{},
+		},
+		{
+			name: "success",
+			body: "a: 1\nb: foo\n",
+			want: structA{A: 1, B: "foo"},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			var (
+				dir   = t.TempDir()
+				path  = filepath.Join(dir, "f.yaml")
+				intoV = reflect.New(reflect.TypeOf(test.want))
+				into  = intoV.Interface()
+			)
+
+			require.NoError(t, os.WriteFile(path, []byte(test.body), 0444))
+			assert.NoError(t, LoadYamlFile(into, path))
+			assert.Equal(t, test.want, intoV.Elem().Interface())
+		})
+	}
+}