io/fs: SubFS.Open returns incorrect errors for invalid paths

[paulhammond]

Go version

go version go1.21.1 linux/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/home/vscode/.cache/go-build'
GOENV='/home/vscode/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/go/pkg/mod'
GONOPROXY='github.com/paulhammond'
GONOSUMDB='github.com/paulhammond'
GOOS='linux'
GOPATH='/go'
GOPRIVATE='github.com/paulhammond'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_arm64'
GOVCS=''
GOVERSION='go1.21.1'
GCCGO='gccgo'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/workspace/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 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2551620224=/tmp/go-build -gno-record-gcc-switches'

What did you do?

The documentation for the fs.FS interface says:

Open should reject attempts to open names that do not satisfy ValidPath(name), returning a *PathError with Err set to ErrInvalid or ErrNotExist.

The errors returned by SubFS.Open() do not fulfill this contract, as demonstrated by https://go.dev/play/p/N5lvehlpeB5. Calling Open with an invalid path returns a *PathError with Err set to errors.New("invalid name") instead. This breaks any code that accepts an fs.FS and attempts to handle the documented errors.

What did you see happen?

err open ./: invalid name
isInvalid false
isNotExist false

What did you expect to see?

err open ./: invalid argument
isInvalid true
isNotExist false

[gopherbot]

Change https://go.dev/cl/560137 mentions this issue: io/fs: set ErrInvalid for FS.Open from SubFS when it fails ValidPath