errors: record only single frame

See Issue #29382 and Issue #30468.

3 frames are no longer needed as of
https://go-review.googlesource.com/c/go/+/152537/

name                     old time/op  new time/op  delta
New-8                     475ns ± 3%   352ns ± 2%  -25.87%  (p=0.008 n=5+5)
Errorf/no_format-8        661ns ± 4%   558ns ± 2%  -15.63%  (p=0.008 n=5+5)
Errorf/with_format-8      729ns ± 6%   626ns ± 2%  -14.23%  (p=0.008 n=5+5)
Errorf/method:_mytype-8  1.00µs ± 9%  0.84µs ± 2%  -15.94%  (p=0.008 n=5+5)
Errorf/method:_number-8  1.25µs ± 7%  1.04µs ± 2%  -16.38%  (p=0.008 n=5+5)

Change-Id: I30377e769b3b3be623f63ecbe365f8950ca08dda
Reviewed-on: https://go-review.googlesource.com/c/go/+/167400
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>

2 files changed, 30 insertions, 16 deletions

diff --git a/src/errors/frame.go b/src/errors/frame.go
index a5369e5c36..487092fa89 100644
--- a/src/errors/frame.go
+++ b/src/errors/frame.go
@@ -10,10 +10,7 @@ import (
 
 // A Frame contains part of a call stack.
 type Frame struct {
-	// Make room for three PCs: the one we were asked for, what it called,
-	// and possibly a PC for skipPleaseUseCallersFrames. See:
-	// https://go.googlesource.com/go/+/032678e0fb/src/runtime/extern.go#169
-	frames [3]uintptr
+	frames [1]uintptr
 }
 
 // Caller returns a Frame that describes a frame on the caller's stack.
@@ -21,7 +18,7 @@ type Frame struct {
 // Caller(0) returns the frame for the caller of Caller.
 func Caller(skip int) Frame {
 	var s Frame
-	runtime.Callers(skip+1, s.frames[:])
+	runtime.Callers(skip+2, s.frames[:])
 	return s
 }
 
@@ -30,13 +27,7 @@ func Caller(skip int) Frame {
 // The returned function may be "" even if file and line are not.
 func (f Frame) location() (function, file string, line int) {
 	frames := runtime.CallersFrames(f.frames[:])
-	if _, ok := frames.Next(); !ok {
-		return "", "", 0
-	}
-	fr, ok := frames.Next()
-	if !ok {
-		return "", "", 0
-	}
+	fr, _ := frames.Next()
 	return fr.Function, fr.File, fr.Line
 }
 
diff --git a/src/errors/frame_test.go b/src/errors/frame_test.go
index 864a6934d1..ba08166966 100644
--- a/src/errors/frame_test.go
+++ b/src/errors/frame_test.go
@@ -9,19 +9,42 @@ import (
 	"errors"
 	"fmt"
 	"math/big"
+	"regexp"
+	"strings"
 	"testing"
 )
 
+func TestFrame(t *testing.T) {
+
+	// Extra line
+	got := fmt.Sprintf("%+v", errors.New("Test"))
+	got = got[strings.Index(got, "Test"):]
+	const want = "^Test:" +
+		"\n    errors_test.TestFrame" +
+		"\n        .*/errors/frame_test.go:20$"
+	ok, err := regexp.MatchString(want, got)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !ok {
+		t.Errorf("\n got %v;\nwant %v", got, want)
+	}
+}
+
 type myType struct{}
 
 func (myType) Format(s fmt.State, v rune) {
 	s.Write(bytes.Repeat([]byte("Hi! "), 10))
 }
 
+func BenchmarkNew(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		_ = errors.New("new error")
+	}
+}
+
 func BenchmarkErrorf(b *testing.B) {
 	err := errors.New("foo")
-	// pi := big.NewFloat(3.14) // Something expensive.
-	num := big.NewInt(5)
 	args := func(a ...interface{}) []interface{} { return a }
 	benchCases := []struct {
 		name   string
@@ -30,8 +53,8 @@ func BenchmarkErrorf(b *testing.B) {
 	}{
 		{"no_format", "msg: %v", args(err)},
 		{"with_format", "failed %d times: %v", args(5, err)},
-		{"method: mytype", "pi: %v", args("myfile.go", myType{}, err)},
-		{"method: number", "pi: %v", args("myfile.go", num, err)},
+		{"method: mytype", "pi %s %v: %v", args("myfile.go", myType{}, err)},
+		{"method: number", "pi %s %d: %v", args("myfile.go", big.NewInt(5), err)},
 	}
 	for _, bc := range benchCases {
 		b.Run(bc.name, func(b *testing.B) {