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os: don't consult Is methods on non-syscall error types
CL #163058 moves interpretation of platform-specific errors to the syscall package. Package syscall errors implement an Is method which os.IsPermission etc. consult. This results in an unintended semantic change to the os package predicate functions: The following program now prints 'true' where it used to print 'false': package main import "os" type myError struct{ error } func (e myError) Is(target error) bool { return target == os.ErrPermission } func main() { println(os.IsPermission(myError{})) } Change the os package error predicate functions to only examine syscall errors, avoiding this semantic change. This CL does retain one minor semantic change: On Plan9, os.IsPermission used to return true for any error with text containing the string "permission denied". It now only returns true for a syscall.ErrorString containing that text. Change-Id: I6b512b1de6ced46c2f1cc8d264fa2495ae7bf9f5 Reviewed-on: https://go-review.googlesource.com/c/go/+/188817 Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org> Reviewed-by: Russ Cox <rsc@golang.org>
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@ -115,7 +115,8 @@ func underlyingErrorIs(err, target error) bool {
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if err == target {
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return true
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}
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e, ok := err.(interface{ Is(error) bool })
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// To preserve prior behavior, only examine syscall errors.
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e, ok := err.(syscallErrorType)
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return ok && e.Is(target)
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}
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11
src/os/error_errno.go
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11
src/os/error_errno.go
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@ -0,0 +1,11 @@
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// Copyright 2019 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build !plan9
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package os
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import "syscall"
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type syscallErrorType = syscall.Errno
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9
src/os/error_plan9.go
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9
src/os/error_plan9.go
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@ -0,0 +1,9 @@
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// Copyright 2019 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package os
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import "syscall"
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type syscallErrorType = syscall.ErrorString
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@ -175,3 +175,13 @@ func TestPathErrorUnwrap(t *testing.T) {
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t.Error("errors.Is failed, wanted success")
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}
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}
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type myErrorIs struct{ error }
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func (e myErrorIs) Is(target error) bool { return target == e.error }
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func TestErrorIsMethods(t *testing.T) {
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if os.IsPermission(myErrorIs{os.ErrPermission}) {
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t.Error("os.IsPermission(err) = true when err.Is(os.ErrPermission), wanted false")
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}
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}
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