New WrapError recognizes any type with Path()

pipelines/pipeline.go

@@ -82,12 +82,12 @@ func (p *Pipeline) Render(w io.Writer, b []byte, filename string, lineNo int, e
 func (p *Pipeline) renderTemplate(src []byte, b map[string]interface{}, filename string, lineNo int) ([]byte, error) {
 	tpl, err := p.liquidEngine.ParseTemplate(src)
 	if err != nil {
-		return nil, utils.WrapPathError(err, "Liquid Error", filename)
+		return nil, utils.WrapPathError(err, filename)
 	}
 	tpl.SetSourceLocation(filename, lineNo)
 	out, err := tpl.Render(b)
 	if err != nil {
-		return nil, utils.WrapPathError(err, "Liquid Error", filename)
+		return nil, utils.WrapPathError(err, filename)
 	}
 	return out, err
 }
@@ -106,7 +106,7 @@ func (p *Pipeline) ApplyLayout(name string, data []byte, e map[string]interface{
 		})
 		data, err = tpl.Render(b)
 		if err != nil {
-			return nil, utils.WrapPathError(err, "render template", name)
+			return nil, utils.WrapPathError(err, name)
 		}
 		name = templates.VariableMap(lfm).String("layout", "")
 	}

site/data.go

@@ -35,7 +35,7 @@ func (s *Site) readDataFiles() error {
 			var d interface{} // map or slice
 			err = utils.UnmarshalYAMLInterface(b, &d)
 			if err != nil {
-				return utils.WrapPathError(err, "read YAML", filename)
+				return utils.WrapPathError(err, filename)
 			}
 			basename := utils.TrimExt(filepath.Base(f.Name()))
 			s.data[basename] = d

site/read.go

@@ -74,7 +74,7 @@ func (s *Site) readFiles() error {
 		defaultFrontmatter := s.config.GetFrontMatterDefaults("", relname)
 		p, err := pages.NewFile(s, filename, filepath.ToSlash(relname), defaultFrontmatter)
 		if err != nil {
-			return utils.WrapPathError(err, "read", filename)
+			return utils.WrapPathError(err, filename)
 		}
 		s.AddDocument(p, true)
 		return nil

utils/errors.go

@@ -0,0 +1,40 @@
+package utils
+
+import (
+	"fmt"
+	"os"
+)
+
+// A PathError is an error with a source path.
+//
+// An os.PathError is unfortunately not a PathError, but this is still
+// useful for deciding whether to wrap other errors.
+type PathError interface {
+	error
+	Path() string
+}
+
+type pathError struct {
+	cause error
+	path  string
+}
+
+func (p *pathError) Error() string {
+	return fmt.Sprintf("%s: %s", p.path, p.cause)
+}
+
+// WrapPathError returns an error that will print with a path.\
+// It wraps its argument if it is not nil and does not already provide a path.
+func WrapPathError(err error, path string) error {
+	if err == nil {
+		return nil
+	}
+	switch err := err.(type) {
+	case PathError:
+		return err
+	case *os.PathError:
+		return err
+	default:
+		return &pathError{path: path, cause: err}
+	}
+}

utils/ioutil.go

@@ -81,21 +81,6 @@ func NewPathError(op, name, text string) *os.PathError {
 	return &os.PathError{Op: op, Path: name, Err: errors.New(text)}
 }
 
-// WrapPathError returns an instance of *os.WrapPathError, by wrapping its argument
-// if it is not already an instance.
-// WrapPathError returns nil for a nil argument.
-func WrapPathError(err error, op, name string) *os.PathError {
-	if err == nil {
-		return nil
-	}
-	switch err := err.(type) {
-	case *os.PathError:
-		return err
-	default:
-		return &os.PathError{Op: op, Path: name, Err: err}
-	}
-}
-
 // RemoveEmptyDirectories recursively removes empty directories.
 func RemoveEmptyDirectories(root string) error {
 	walkFn := func(name string, info os.FileInfo, err error) error {