path/filepath: Rel is not returning an error for symlinks

[mfbx9da4]

Go version

go version go1.22.1 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/da/Library/Caches/go-build'
GOENV='/Users/da/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/da/go/pkg/mod'
GONOPROXY='github.com/speakeasy-api/*'
GONOSUMDB='github.com/speakeasy-api/*'
GOOS='darwin'
GOPATH='/Users/da/go'
GOPRIVATE='github.com/speakeasy-api/*'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.22.1/libexec'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.22.1/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.22.1'
GCCGO='gccgo'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/Users/da/code/speakeasy/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 -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/9w/3j0xt3p530d10gz0w8v926l00000gn/T/go-build564162317=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

filpath.Rel(`/tmp/foo`, `/Users/me/file.txt`) // returns ../../Users/me/file.txt

This returned value is broken as /tmp is actually a symlink. I would expect the method to return an error because the docs say "An error is returned if targpath can't be made relative to basepath"

lrwxr-xr-x@ 1 root  wheel    11B 29 Feb 04:05 /tmp -> private/tmp

What did you see happen?

See above

What did you expect to see?

See above

[adonovan]

By design, Rel is a purely lexical operation. It doesn't interact with the file system, so it cannot tell nor does it care that some path segments are symbolic links. It fails only when called on arguments such as ("..", ".") or ("/a", "a"), where the answer would depend on os.Getwd, or ("C:\foo", "D:\bar"), as there is no relative path that spans Windows volumes.

So Rel is working as intended.