os: dirFS.ReadFile returns inconsistent PathError.Path #64366
Description
Go version
go version devel go1.22-3188758653 Fri Nov 10 21:25:30 2023 +0000 linux/amd64
Reproducibility
- Does this issue reproduce with the latest release?
What operating system and processor architecture are you using (go env)?
GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/rogpeppe/.cache/go-build'
GOENV='/home/rogpeppe/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/rogpeppe/src/go/pkg/mod'
GONOPROXY='github.com/cue-unity'
GONOSUMDB='github.com/cue-unity'
GOOS='linux'
GOPATH='/home/rogpeppe/src/go'
GOPRIVATE='github.com/cue-unity'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/rogpeppe/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/rogpeppe/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='devel go1.22-3188758653 Fri Nov 10 21:25:30 2023 +0000'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/rogpeppe/go/src/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build683023569=/tmp/go-build -gno-record-gcc-switches'What did you do?
https://go.dev/play/p/5vKYCOeV5gd
package main
import (
"errors"
"fmt"
"io/fs"
"os"
)
func main() {
fsys := os.DirFS("/")
_, err := fs.ReadFile(fsys, "non-existent")
fmt.Printf("ReadFile path %q\n", errorPath(err))
_, err = fs.ReadFile(struct{ fs.FS }{fsys}, "non-existent")
fmt.Printf("ReadFile without shortcut: path %q\n", errorPath(err))
}
func errorPath(err error) string {
var perr *fs.PathError
if !errors.As(err, &perr) {
return ""
}
return perr.Path
}
What did you expect to see?
ReadFile path "non-existent"
ReadFile without shortcut: path "non-existent"
What did you see instead?
ReadFile path "/non-existent"
ReadFile without shortcut: path "non-existent"
The PathError returned from fs.ReadFile is reflecting the path of the underlying os implementation rather than the fs.FS name. It should be the same regardless of whether the FS implementation implements ReadFile or not.
I think the dirFS.ReadFile method should probably inspect the returned error and transform paths when it's a PathError.
Also, the io/fs documentation could be clearer about the requirements for error returns throughout the API.