File path comparison without canonicalizing

[estebank]

What it does

When comparing paths, std does this purely on a string equality basis, which will fail with things like symlinks or relative paths. We should be recommending people use std::fs::canonicalize to avoid mistakes.

Advantage

Using canonicalize on a Path makes it so that there are no possibilities of paths that are supposed to be equal ever being considered different.

Drawbacks

No response

Example

    let p = std::path::Path::new("foo/../foo");
    p == Path::new("foo");
    p == "foo";

Could be written as:

    std::fs::canonicalize(p) == Path::new("foo");
    std::fs::canonicalize(p) == "foo";

Comparison with existing lints

No response

Additional Context

This is one of the bugs found in uutils by Canonical's audit: https://corrode.dev/blog/bugs-rust-wont-catch/#string-equality-on-paths-is-not-the-same-as-filesystem-identity

[collinfunk]

Canonicalization can be extremely slow. I would be very careful suggesting it. It causes the following poor performance, for example:

$ mkdir -p $(yes a/ | head -n $((32 * 1024)) | tr -d '\n')
$ while cd $(yes a/ | head -n 1024 | tr -d '\n'); do :; done 2>/dev/null
$ echo a > file
$ time cp file copy

real 0m0.010s
user 0m0.002s
sys 0m0.003s
$ time uu_cp file copy

real 0m12.857s
user 0m0.064s
sys 0m12.702s