ACP: `Path::is_empty` (original) (raw)

Proposal

Problem statement

There's not a straight forward way to check if a path is empty.

Motivating examples or use cases

An empty path is almost never valid. For example, passing it to most OS filesystem APIs will always result in an error. Moreover it is a potential footgun when joining paths. At most it will append a /, otherwise it's a no-op. This can be a (albeit limited) form of path traversal attack, like . or .. where you end up addressing the parent instead of the child you assumed.

Solution sketch

impl Path { fn is_empty(&self) -> bool; }

This is just a helper; it does not add anything that can't be done today (see alternatives). It is however more convenient and provides a place to hang some documentation on the issue.

Alternatives

Don't add this. There is already path.components().next().is_none() and path.as_os_str().is_empty().

This was previously rejected back in 2016, see rust-lang/rust#31877 (comment).

Querying a Path should exclusively go through the components iterator as that's basically how a path is always interpreted. Querying the backing storage can always be done via as_os_str (as pointed out), and that's likely good enough for now.

Put another way, testing whether a path is empty by looking at the length of the underlying bytes is probably "just the wrong question to ask", and instead the components iterator should be queried to see if it's empty.

But I'm not aware of a case where components would return empty but as_os_str wouldn't (or vice versa). Please do correct me if I'm wrong.

Github shows ~8.3k results for .as_os_str().is_empty(). While not all of them may be to do with Path, from my cursory look it does seem Path dominates the results.

What happens now?

This issue contains an API change proposal (or ACP) and is part of the libs-api team feature lifecycle. Once this issue is filed, the libs-api team will review open proposals as capability becomes available. Current response times do not have a clear estimate, but may be up to several months.

Possible responses

The libs team may respond in various different ways. First, the team will consider the problem (this doesn't require any concrete solution or alternatives to have been proposed):

We think this problem seems worth solving, and the standard library might be the right place to solve it.
We think that this probably doesn't belong in the standard library.

Second, if there's a concrete solution:

We think this specific solution looks roughly right, approved, you or someone else should implement this. (Further review will still happen on the subsequent implementation PR.)
We're not sure this is the right solution, and the alternatives or other materials don't give us enough information to be sure about that. Here are some questions we have that aren't answered, or rough ideas about alternatives we'd want to see discussed.

ACP: Path::is_empty (original) (raw)