path/filepath: Dir() returns incorrect result if the path contains a trailing slash

[0xmohit]

filepath.Dir returns incorrect result if the specified path contains a trailing slash. For example, if the input were /home/, then filepath.Dir and filepath.Base return /home and home respectively. Playground link.

Following is the output of dirname and basename from GNU coreutils:

$ dirname /home
/
$ basename /home
home
$ dirname /home/
/
$ basename /home/
home

When the input doesn't contain a trailing slash, then the functions yield expected output.

[adg]

There does seem to be an inconsistency between filepath.Dir and filepath.Base. IMO Dir should not include the component returned by Base.

[gopherbot]

CL https://golang.org/cl/16791 mentions this issue.

[rsc]

The docs for Dir say "Dir returns all but the last element of path, typically the path's directory." They don't guarantee to get the path's directory. See my longer comment on CL 16791, but I don't think we should change this.

[0xmohit]

This was specifically regarding the oddity in the current implementation (the second case in the playground link above):

input path: /home/, dir: /home, base: home

Whether Dir returns /home or / in this case, Base should adjust itself. To elaborate, one would expect that

filepath.Clean(p) == filepath.Join(filepath.Dir(p), filepath.Base(p))

[rsc]

@0xmohit that's not guaranteed by the docs. The docs state different behaviors for Dir and Base, and I don't feel at liberty to contradict the established behavior and docs. If you need that guarantee, use filepath.Split.