Make Stacker easier for other types to implement.

errors.go

@@ -29,30 +29,9 @@ func (w *wrapped) Error() string {
 	return w.err.Error()
 }
 
-// Stack returns a slice of [Frame]
-// representing the call stack at the point [Wrap] was called.
-func (w *wrapped) Stack() Frames {
-	var (
-		rframes = runtime.CallersFrames(w.stack)
-		result  []Frame
-	)
-
-	for {
-		rframe, more := rframes.Next()
-		if rframe.PC == 0 {
-			break
-		}
-		result = append(result, Frame{
-			Function: rframe.Function,
-			File:     rframe.File,
-			Line:     rframe.Line,
-		})
-		if !more {
-			break
-		}
-	}
-
-	return result
+// Stack implements the [Stacker] interface.
+func (w *wrapped) Stack() []uintptr {
+	return w.stack
 }
 
 func dowrap(err error) error {
@@ -64,19 +43,20 @@ func dowrap(err error) error {
 
 	const maxdepth = 32
 	var pcs [maxdepth]uintptr
-	n := runtime.Callers(3, pcs[:]) // skip runtime.Callers, dowrap, and the Wrap/Wrapf/New/Newf call that got us here.
+	n := runtime.Callers(3, pcs[:]) // 3 skips runtime.Callers, dowrap (this function), and the Wrap/Wrapf/New/Newf call that got us here.
 	return &wrapped{
 		err:   err,
 		stack: pcs[:n],
 	}
 }
 
 // Stacker is the interface implemented by errors with a stack trace.
+// Types wishing to implement Stacker can use [runtime.Callers] to get the call stack.
 type Stacker interface {
-	Stack() Frames
+	Stack() []uintptr
 }
 
-// Stack returns the stack trace from an error.
+// Stack returns the stack trace from an error as a [Frames].
 // If the error is nil or does not contain a stack trace,
 // Stack returns nil.
 func Stack(e error) Frames {
@@ -88,7 +68,29 @@ func Stack(e error) Frames {
 	if !As(e, &s) {
 		return nil
 	}
-	return s.Stack()
+
+	var (
+		pcs     = s.Stack()
+		rframes = runtime.CallersFrames(pcs)
+		result  []Frame
+	)
+
+	for {
+		rframe, more := rframes.Next()
+		if rframe.PC == 0 {
+			break
+		}
+		result = append(result, Frame{
+			Function: rframe.Function,
+			File:     rframe.File,
+			Line:     rframe.Line,
+		})
+		if !more {
+			break
+		}
+	}
+
+	return result
 }
 
 // Frames is a slice of [Frame].