BasePathFs wrongly trims path prefix.

[movsb]

It seems that BasePathFile.Name() method returns wrongly trimmed path:

afero/basepath.go

Line 37 in 5c4385a

return strings.TrimPrefix(sourcename, filepath.Clean(f.path))

filepath.Clean will have the last / removed, leaving the Name() containing a / prefix.
Next time the BasePathFile trimming a prefix, it trims nothing: strings.TrimPrefix(`/123/afero-test-388191401`, `123`).

package main

import (
	"fmt"

	"github.com/spf13/afero"
)

func must1[A any](a A, e error) A {
	if e != nil {
		panic(e)
	}
	return a
}
func must(e error) {
	if e != nil {
		panic(e)
	}
}

func main() {
	osFs := afero.NewOsFs()
	must(osFs.MkdirAll(`files/123`, 0755))

	fs1 := afero.NewBasePathFs(osFs, `files`)
	fs2 := afero.NewBasePathFs(fs1, `123`)

	tmp := must1(afero.TempFile(fs2, `.`, `afero-test-*`))
	fmt.Println(`Path:`, tmp.Name())

	must(fs2.Chmod(tmp.Name(), 0644))
}

The code above will panic:

$ go run main.go
Path: /123/afero-test-388191401
panic: chmod files/123/123/afero-test-388191401: no such file or directory

goroutine 1 [running]:
main.must(...)
        /Users/.../code/tests/main.go:17
main.main()
        /Users/.../code/tests/main.go:31 +0x1b8
exit status 2

Update:

Chaning fs2 to be fs2 := afero.NewBasePathFs(fs1, `/123`) seems to work, but it's somewhat inconsistent.