fmt: make type of fmt.Errorf the same as that of errors.New

This applies only for cases where %w is not used.

The purpose of this change is to reduce test failures where tests
depend on these two being the same type, as they previously were.

Change-Id: I2dd28b93fe1d59f3cfbb4eb0875d1fb8ee699746
Reviewed-on: https://go-review.googlesource.com/c/go/+/167402
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>

1 files changed, 18 insertions, 3 deletions

diff --git a/src/errors/errors.go b/src/errors/errors.go
index ebb136cdd4..51175b13c8 100644
--- a/src/errors/errors.go
+++ b/src/errors/errors.go
@@ -5,7 +5,10 @@
 // Package errors implements functions to manipulate errors.
 package errors
 
-import "runtime"
+import (
+	"internal/errinternal"
+	"runtime"
+)
 
 // New returns an error that formats as the given text.
 //
@@ -15,21 +18,33 @@ func New(text string) error {
 	// Inline call to errors.Callers to improve performance.
 	var s Frame
 	runtime.Callers(2, s.frames[:])
-	return &errorString{text, s}
+	return &errorString{text, nil, s}
+}
+
+func init() {
+	errinternal.NewError = func(text string, err error) error {
+		var s Frame
+		runtime.Callers(3, s.frames[:])
+		return &errorString{text, err, s}
+	}
 }
 
 // errorString is a trivial implementation of error.
 type errorString struct {
 	s     string
+	err   error
 	frame Frame
 }
 
 func (e *errorString) Error() string {
+	if e.err != nil {
+		return e.s + ": " + e.err.Error()
+	}
 	return e.s
 }
 
 func (e *errorString) FormatError(p Printer) (next error) {
 	p.Print(e.s)
 	e.frame.Format(p)
-	return nil
+	return e.err
 }