From 14491a2ec499668388d7fe7e95b84dbf0e1cf04d Mon Sep 17 00:00:00 2001 From: Damien Neil Date: Mon, 13 May 2019 16:46:31 -0700 Subject: fmt: support %w When fmt.Errorf is provided with a %w verb with an error operand, return an error implementing an Unwrap method returning that operand. It is invalid to use %w with other formatting functions, to use %w multiple times in a format string, or to use %w with a non-error operand. When the Errorf format string contains an invalid use of %w, the returned error does not implement Unwrap. Change-Id: I534e20d3b163ab22c2b137b1c9095906dc243221 Reviewed-on: https://go-review.googlesource.com/c/go/+/176998 Reviewed-by: Marcel van Lohuizen --- src/fmt/errors.go | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) create mode 100644 src/fmt/errors.go (limited to 'src/fmt/errors.go') diff --git a/src/fmt/errors.go b/src/fmt/errors.go new file mode 100644 index 0000000000..6ae6c47fd9 --- /dev/null +++ b/src/fmt/errors.go @@ -0,0 +1,43 @@ +// Copyright 2018 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package fmt + +import "errors" + +// Errorf formats according to a format specifier and returns the string as a +// value that satisfies error. +// +// If the format specifier includes a %w verb with an error operand, +// the returned error will implement an Unwrap method returning the operand. It is +// invalid to include more than one %w verb or to supply it with an operand +// that does not implement the error innterface. The %w verb is otherwise +// a synonym for %v. +func Errorf(format string, a ...interface{}) error { + p := newPrinter() + p.wrapErrs = true + p.doPrintf(format, a) + s := string(p.buf) + var err error + if p.wrappedErr == nil { + err = errors.New(s) + } else { + err = &wrapError{s, p.wrappedErr} + } + p.free() + return err +} + +type wrapError struct { + msg string + err error +} + +func (e *wrapError) Error() string { + return e.msg +} + +func (e *wrapError) Unwrap() error { + return e.err +} -- cgit v1.3-5-g9baa