Proxy: Rewrite internal/errors on stdlib with a single withStack struct.

Replaces the pkg/errors fork with a thin wrapper over the standard
library's errors package. A single withStack struct captures stack
traces via runtime.Callers, while fmt.Errorf("%w", ...) handles all
message wrapping. This enables errors.Is/As/Unwrap chain traversal
(the fork silently broke them) and deletes ~190 lines of stack/frame
formatting code. Adds table-driven tests at 100% statement coverage.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
winlin 2026-04-19 18:36:59 -04:00
parent cd11a6720f
commit f7f0676c9e
3 changed files with 323 additions and 394 deletions

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@ -1,270 +1,153 @@
// Package errors provides simple error handling primitives.
// Package errors provides error handling primitives with stack traces.
//
// The traditional error handling idiom in Go is roughly akin to
//
// if err != nil {
// return err
// }
//
// which applied recursively up the call stack results in error reports
// without context or debugging information. The errors package allows
// programmers to add context to the failure path in their code in a way
// that does not destroy the original value of the error.
// It is a thin layer over the standard library's errors package, adding a
// stack trace at the point an error is created or wrapped. The wrapping
// chain is fully compatible with errors.Is, errors.As, and errors.Unwrap.
//
// # Adding context to an error
//
// The errors.Wrap function returns a new error that adds context to the
// original error by recording a stack trace at the point Wrap is called,
// and the supplied message. For example
//
// _, err := ioutil.ReadAll(r)
// _, err := io.ReadAll(r)
// if err != nil {
// return errors.Wrap(err, "read failed")
// }
//
// If additional control is required the errors.WithStack and errors.WithMessage
// functions destructure errors.Wrap into its component operations of annotating
// an error with a stack trace and an a message, respectively.
//
// # Retrieving the cause of an error
//
// Using errors.Wrap constructs a stack of errors, adding context to the
// preceding error. Depending on the nature of the error it may be necessary
// to reverse the operation of errors.Wrap to retrieve the original error
// for inspection. Any error value which implements this interface
//
// type causer interface {
// Cause() error
// }
//
// can be inspected by errors.Cause. errors.Cause will recursively retrieve
// the topmost error which does not implement causer, which is assumed to be
// the original cause. For example:
//
// switch err := errors.Cause(err).(type) {
// case *MyError:
// // handle specifically
// default:
// // unknown error
// }
//
// causer interface is not exported by this package, but is considered a part
// of stable public API.
//
// # Formatted printing of errors
//
// All error values returned from this package implement fmt.Formatter and can
// be formatted by the fmt package. The following verbs are supported
// %s the error message (full wrap chain)
// %v same as %s
// %+v the error message followed by the captured stack trace
// %q the error message, quoted
//
// %s print the error. If the error has a Cause it will be
// printed recursively
// %v see %s
// %+v extended format. Each Frame of the error's StackTrace will
// be printed in detail.
// # Retrieving the stack trace
//
// # Retrieving the stack trace of an error or wrapper
//
// New, Errorf, Wrap, and Wrapf record a stack trace at the point they are
// invoked. This information can be retrieved with the following interface.
// Errors returned by this package satisfy the following interface:
//
// type stackTracer interface {
// StackTrace() errors.StackTrace
// StackTrace() []uintptr
// }
//
// Where errors.StackTrace is defined as
//
// type StackTrace []Frame
//
// The Frame type represents a call site in the stack trace. Frame supports
// the fmt.Formatter interface that can be used for printing information about
// the stack trace of this error. For example:
//
// if err, ok := err.(stackTracer); ok {
// for _, f := range err.StackTrace() {
// fmt.Printf("%+s:%d", f)
// }
// }
//
// stackTracer interface is not exported by this package, but is considered a part
// of stable public API.
//
// See the documentation for Frame.Format for more details.
// Fork from https://github.com/pkg/errors
package errors
import (
"errors"
"fmt"
"io"
"runtime"
)
// New returns an error with the supplied message.
// New also records the stack trace at the point it was called.
func New(message string) error {
return &fundamental{
msg: message,
stack: callers(),
}
// Re-exported stdlib primitives so callers can use a single import.
var (
Is = errors.Is
As = errors.As
Unwrap = errors.Unwrap
Join = errors.Join
)
// withStack wraps an error with a captured stack trace.
type withStack struct {
err error
pcs []uintptr
}
// Errorf formats according to a format specifier and returns the string
// as a value that satisfies error.
// Errorf also records the stack trace at the point it was called.
func Errorf(format string, args ...interface{}) error {
return &fundamental{
msg: fmt.Sprintf(format, args...),
stack: callers(),
}
func (e *withStack) Error() string {
return e.err.Error()
}
// fundamental is an error that has a message and a stack, but no caller.
type fundamental struct {
msg string
*stack
func (e *withStack) Unwrap() error {
return e.err
}
func (f *fundamental) Error() string { return f.msg }
func (e *withStack) StackTrace() []uintptr {
return e.pcs
}
func (f *fundamental) Format(s fmt.State, verb rune) {
func (e *withStack) Format(s fmt.State, verb rune) {
switch verb {
case 'v':
if s.Flag('+') {
io.WriteString(s, f.msg)
f.stack.Format(s, verb)
fmt.Fprint(s, e.err.Error())
frames := runtime.CallersFrames(e.pcs)
for {
f, more := frames.Next()
fmt.Fprintf(s, "\n%s\n\t%s:%d", f.Function, f.File, f.Line)
if !more {
break
}
}
return
}
fallthrough
case 's':
io.WriteString(s, f.msg)
fmt.Fprint(s, e.err.Error())
case 'q':
fmt.Fprintf(s, "%q", f.msg)
fmt.Fprintf(s, "%q", e.err.Error())
}
}
func callers() []uintptr {
var pcs [32]uintptr
n := runtime.Callers(3, pcs[:])
return pcs[:n]
}
func attach(err error) error {
return &withStack{err: err, pcs: callers()}
}
// New returns an error with the supplied message and a captured stack trace.
func New(message string) error {
return attach(errors.New(message))
}
// Errorf formats according to a format specifier and returns a new error with
// a captured stack trace. It supports %w for wrapping an existing error.
func Errorf(format string, args ...any) error {
return attach(fmt.Errorf(format, args...))
}
// WithStack annotates err with a stack trace at the point WithStack was called.
// If err is nil, WithStack returns nil.
func WithStack(err error) error {
if err == nil {
return nil
}
return &withStack{
err,
callers(),
}
return attach(err)
}
type withStack struct {
error
*stack
}
func (w *withStack) Cause() error { return w.error }
func (w *withStack) Format(s fmt.State, verb rune) {
switch verb {
case 'v':
if s.Flag('+') {
fmt.Fprintf(s, "%+v", w.Cause())
w.stack.Format(s, verb)
return
}
fallthrough
case 's':
io.WriteString(s, w.Error())
case 'q':
fmt.Fprintf(s, "%q", w.Error())
}
}
// Wrap returns an error annotating err with a stack trace
// at the point Wrap is called, and the supplied message.
// If err is nil, Wrap returns nil.
func Wrap(err error, message string) error {
if err == nil {
return nil
}
err = &withMessage{
cause: err,
msg: message,
}
return &withStack{
err,
callers(),
}
}
// Wrapf returns an error annotating err with a stack trace
// at the point Wrapf is call, and the format specifier.
// If err is nil, Wrapf returns nil.
func Wrapf(err error, format string, args ...interface{}) error {
if err == nil {
return nil
}
err = &withMessage{
cause: err,
msg: fmt.Sprintf(format, args...),
}
return &withStack{
err,
callers(),
}
}
// WithMessage annotates err with a new message.
// WithMessage annotates err with a new message, without capturing a stack.
// If err is nil, WithMessage returns nil.
func WithMessage(err error, message string) error {
if err == nil {
return nil
}
return &withMessage{
cause: err,
msg: message,
return fmt.Errorf("%s: %w", message, err)
}
// Wrap returns an error annotating err with a message and a captured stack.
// If err is nil, Wrap returns nil.
func Wrap(err error, message string) error {
if err == nil {
return nil
}
return attach(fmt.Errorf("%s: %w", message, err))
}
type withMessage struct {
cause error
msg string
}
func (w *withMessage) Error() string { return w.msg + ": " + w.cause.Error() }
func (w *withMessage) Cause() error { return w.cause }
func (w *withMessage) Format(s fmt.State, verb rune) {
switch verb {
case 'v':
if s.Flag('+') {
fmt.Fprintf(s, "%+v\n", w.Cause())
io.WriteString(s, w.msg)
return
}
fallthrough
case 's', 'q':
io.WriteString(s, w.Error())
// Wrapf is the formatting variant of Wrap.
// If err is nil, Wrapf returns nil.
func Wrapf(err error, format string, args ...any) error {
if err == nil {
return nil
}
return attach(fmt.Errorf(fmt.Sprintf(format, args...)+": %w", err))
}
// Cause returns the underlying cause of the error, if possible.
// An error value has a cause if it implements the following
// interface:
//
// type causer interface {
// Cause() error
// }
//
// If the error does not implement Cause, the original error will
// be returned. If the error is nil, nil will be returned without further
// investigation.
// Cause walks the error's Unwrap chain and returns the root error.
// New code should prefer errors.Is or errors.As.
func Cause(err error) error {
type causer interface {
Cause() error
}
for err != nil {
cause, ok := err.(causer)
if !ok {
break
u := errors.Unwrap(err)
if u == nil {
return err
}
err = cause.Cause()
err = u
}
return err
return nil
}

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@ -0,0 +1,233 @@
// Copyright (c) 2026 Winlin
//
// SPDX-License-Identifier: MIT
package errors
import (
stderrors "errors"
"fmt"
"strings"
"testing"
)
func TestNew_MessageAndStack(t *testing.T) {
err := New("boom")
if err == nil {
t.Fatal("New returned nil")
}
if err.Error() != "boom" {
t.Fatalf("Error() = %q, want %q", err.Error(), "boom")
}
ws, ok := err.(*withStack)
if !ok {
t.Fatalf("New did not return *withStack, got %T", err)
}
if len(ws.StackTrace()) == 0 {
t.Fatal("StackTrace is empty")
}
}
func TestErrorf_FormatsMessage(t *testing.T) {
err := Errorf("code=%d reason=%s", 42, "oops")
if err.Error() != "code=42 reason=oops" {
t.Fatalf("Error() = %q", err.Error())
}
}
func TestErrorf_SupportsWrapVerb(t *testing.T) {
root := stderrors.New("root")
err := Errorf("ctx: %w", root)
if !stderrors.Is(err, root) {
t.Fatal("errors.Is did not find root through Errorf(%w)")
}
}
func TestWithStack_NilReturnsNil(t *testing.T) {
if got := WithStack(nil); got != nil {
t.Fatalf("WithStack(nil) = %v, want nil", got)
}
}
func TestWithStack_PreservesMessage(t *testing.T) {
inner := stderrors.New("plain")
err := WithStack(inner)
if err.Error() != "plain" {
t.Fatalf("Error() = %q, want %q", err.Error(), "plain")
}
if !stderrors.Is(err, inner) {
t.Fatal("errors.Is did not find inner through WithStack")
}
}
func TestWithMessage_NilReturnsNil(t *testing.T) {
if got := WithMessage(nil, "ignored"); got != nil {
t.Fatalf("WithMessage(nil) = %v, want nil", got)
}
}
func TestWithMessage_PrependsAndWraps(t *testing.T) {
inner := stderrors.New("root")
err := WithMessage(inner, "ctx")
if err.Error() != "ctx: root" {
t.Fatalf("Error() = %q", err.Error())
}
if !stderrors.Is(err, inner) {
t.Fatal("errors.Is did not traverse WithMessage")
}
// WithMessage must not capture a stack — verify the result is not a *withStack.
if _, ok := err.(*withStack); ok {
t.Fatal("WithMessage should not attach a stack")
}
}
func TestWrap_NilReturnsNil(t *testing.T) {
if got := Wrap(nil, "ignored"); got != nil {
t.Fatalf("Wrap(nil) = %v, want nil", got)
}
}
func TestWrap_MessageAndStackAndChain(t *testing.T) {
inner := stderrors.New("root")
err := Wrap(inner, "ctx")
if err.Error() != "ctx: root" {
t.Fatalf("Error() = %q", err.Error())
}
ws, ok := err.(*withStack)
if !ok {
t.Fatalf("Wrap did not return *withStack, got %T", err)
}
if len(ws.StackTrace()) == 0 {
t.Fatal("StackTrace is empty")
}
if !stderrors.Is(err, inner) {
t.Fatal("errors.Is did not traverse Wrap")
}
}
func TestWrapf_NilReturnsNil(t *testing.T) {
if got := Wrapf(nil, "ignored %d", 1); got != nil {
t.Fatalf("Wrapf(nil) = %v, want nil", got)
}
}
func TestWrapf_FormatsAndChains(t *testing.T) {
inner := stderrors.New("root")
err := Wrapf(inner, "ctx=%d op=%s", 7, "read")
if err.Error() != "ctx=7 op=read: root" {
t.Fatalf("Error() = %q", err.Error())
}
if !stderrors.Is(err, inner) {
t.Fatal("errors.Is did not traverse Wrapf")
}
}
func TestCause_NilReturnsNil(t *testing.T) {
if got := Cause(nil); got != nil {
t.Fatalf("Cause(nil) = %v, want nil", got)
}
}
func TestCause_NoUnwrapReturnsSelf(t *testing.T) {
root := stderrors.New("root")
if got := Cause(root); got != root {
t.Fatalf("Cause(root) = %v, want root", got)
}
}
func TestCause_WalksToRoot(t *testing.T) {
root := stderrors.New("root")
err := Wrap(Wrap(WithMessage(root, "a"), "b"), "c")
if got := Cause(err); got != root {
t.Fatalf("Cause = %v, want root", got)
}
}
func TestUnwrap_ReturnsInner(t *testing.T) {
inner := stderrors.New("inner")
err := WithStack(inner)
if got := stderrors.Unwrap(err); got != inner {
t.Fatalf("Unwrap = %v, want inner", got)
}
}
func TestFormat_S(t *testing.T) {
err := New("msg")
got := fmt.Sprintf("%s", err)
if got != "msg" {
t.Fatalf("%%s = %q, want %q", got, "msg")
}
}
func TestFormat_VFallsThroughToS(t *testing.T) {
err := New("msg")
got := fmt.Sprintf("%v", err)
if got != "msg" {
t.Fatalf("%%v = %q, want %q", got, "msg")
}
}
func TestFormat_VPlusIncludesStack(t *testing.T) {
err := New("msg")
got := fmt.Sprintf("%+v", err)
if !strings.HasPrefix(got, "msg") {
t.Fatalf("%%+v output does not start with message: %q", got)
}
// Must include this test function in the captured stack.
if !strings.Contains(got, "TestFormat_VPlusIncludesStack") {
t.Fatalf("%%+v output missing caller frame:\n%s", got)
}
// Must include a file:line reference.
if !strings.Contains(got, "errors_test.go:") {
t.Fatalf("%%+v output missing file:line:\n%s", got)
}
}
func TestFormat_Q(t *testing.T) {
err := New("msg")
got := fmt.Sprintf("%q", err)
if got != `"msg"` {
t.Fatalf("%%q = %q, want %q", got, `"msg"`)
}
}
func TestIs_ThroughWrapChain(t *testing.T) {
sentinel := stderrors.New("sentinel")
err := Wrap(WithMessage(WithStack(sentinel), "mid"), "outer")
if !stderrors.Is(err, sentinel) {
t.Fatal("errors.Is failed to traverse Wrap/WithMessage/WithStack chain")
}
}
type typedErr struct{ code int }
func (t *typedErr) Error() string { return fmt.Sprintf("typed(%d)", t.code) }
func TestAs_ThroughWrapChain(t *testing.T) {
target := &typedErr{code: 7}
err := Wrap(WithStack(target), "ctx")
var got *typedErr
if !stderrors.As(err, &got) {
t.Fatal("errors.As failed to find *typedErr in chain")
}
if got.code != 7 {
t.Fatalf("As returned code=%d, want 7", got.code)
}
}
func TestReExports_AreStdlib(t *testing.T) {
// Sanity: the re-exports must actually be the stdlib functions.
a := stderrors.New("a")
b := stderrors.New("b")
joined := Join(a, b)
if !Is(joined, a) || !Is(joined, b) {
t.Fatal("Join/Is re-exports do not match stdlib behavior")
}
if Unwrap(WithStack(a)) != a {
t.Fatal("Unwrap re-export does not match stdlib behavior")
}
var target *typedErr
te := &typedErr{code: 1}
if !As(WithStack(te), &target) {
t.Fatal("As re-export does not match stdlib behavior")
}
}

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@ -1,187 +0,0 @@
// Fork from https://github.com/pkg/errors
package errors
import (
"fmt"
"io"
"path"
"runtime"
"strings"
)
// Frame represents a program counter inside a stack frame.
type Frame uintptr
// pc returns the program counter for this frame;
// multiple frames may have the same PC value.
func (f Frame) pc() uintptr { return uintptr(f) - 1 }
// file returns the full path to the file that contains the
// function for this Frame's pc.
func (f Frame) file() string {
fn := runtime.FuncForPC(f.pc())
if fn == nil {
return "unknown"
}
file, _ := fn.FileLine(f.pc())
return file
}
// line returns the line number of source code of the
// function for this Frame's pc.
func (f Frame) line() int {
fn := runtime.FuncForPC(f.pc())
if fn == nil {
return 0
}
_, line := fn.FileLine(f.pc())
return line
}
// Format formats the frame according to the fmt.Formatter interface.
//
// %s source file
// %d source line
// %n function name
// %v equivalent to %s:%d
//
// Format accepts flags that alter the printing of some verbs, as follows:
//
// %+s path of source file relative to the compile time GOPATH
// %+v equivalent to %+s:%d
func (f Frame) Format(s fmt.State, verb rune) {
switch verb {
case 's':
switch {
case s.Flag('+'):
pc := f.pc()
fn := runtime.FuncForPC(pc)
if fn == nil {
io.WriteString(s, "unknown")
} else {
file, _ := fn.FileLine(pc)
fmt.Fprintf(s, "%s\n\t%s", fn.Name(), file)
}
default:
io.WriteString(s, path.Base(f.file()))
}
case 'd':
fmt.Fprintf(s, "%d", f.line())
case 'n':
name := runtime.FuncForPC(f.pc()).Name()
io.WriteString(s, funcname(name))
case 'v':
f.Format(s, 's')
io.WriteString(s, ":")
f.Format(s, 'd')
}
}
// StackTrace is stack of Frames from innermost (newest) to outermost (oldest).
type StackTrace []Frame
// Format formats the stack of Frames according to the fmt.Formatter interface.
//
// %s lists source files for each Frame in the stack
// %v lists the source file and line number for each Frame in the stack
//
// Format accepts flags that alter the printing of some verbs, as follows:
//
// %+v Prints filename, function, and line number for each Frame in the stack.
func (st StackTrace) Format(s fmt.State, verb rune) {
switch verb {
case 'v':
switch {
case s.Flag('+'):
for _, f := range st {
fmt.Fprintf(s, "\n%+v", f)
}
case s.Flag('#'):
fmt.Fprintf(s, "%#v", []Frame(st))
default:
fmt.Fprintf(s, "%v", []Frame(st))
}
case 's':
fmt.Fprintf(s, "%s", []Frame(st))
}
}
// stack represents a stack of program counters.
type stack []uintptr
func (s *stack) Format(st fmt.State, verb rune) {
switch verb {
case 'v':
switch {
case st.Flag('+'):
for _, pc := range *s {
f := Frame(pc)
fmt.Fprintf(st, "\n%+v", f)
}
}
}
}
func (s *stack) StackTrace() StackTrace {
f := make([]Frame, len(*s))
for i := 0; i < len(f); i++ {
f[i] = Frame((*s)[i])
}
return f
}
func callers() *stack {
const depth = 32
var pcs [depth]uintptr
n := runtime.Callers(3, pcs[:])
var st stack = pcs[0:n]
return &st
}
// funcname removes the path prefix component of a function's name reported by func.Name().
func funcname(name string) string {
i := strings.LastIndex(name, "/")
name = name[i+1:]
i = strings.Index(name, ".")
return name[i+1:]
}
func trimGOPATH(name, file string) string {
// Here we want to get the source file path relative to the compile time
// GOPATH. As of Go 1.6.x there is no direct way to know the compiled
// GOPATH at runtime, but we can infer the number of path segments in the
// GOPATH. We note that fn.Name() returns the function name qualified by
// the import path, which does not include the GOPATH. Thus we can trim
// segments from the beginning of the file path until the number of path
// separators remaining is one more than the number of path separators in
// the function name. For example, given:
//
// GOPATH /home/user
// file /home/user/src/pkg/sub/file.go
// fn.Name() pkg/sub.Type.Method
//
// We want to produce:
//
// pkg/sub/file.go
//
// From this we can easily see that fn.Name() has one less path separator
// than our desired output. We count separators from the end of the file
// path until it finds two more than in the function name and then move
// one character forward to preserve the initial path segment without a
// leading separator.
const sep = "/"
goal := strings.Count(name, sep) + 2
i := len(file)
for n := 0; n < goal; n++ {
i = strings.LastIndex(file[:i], sep)
if i == -1 {
// not enough separators found, set i so that the slice expression
// below leaves file unmodified
i = -len(sep)
break
}
}
// get back to 0 or trim the leading separator
file = file[i+len(sep):]
return file
}