Path::strip_prefix() improperly strips trailing slash

[MikkelPaulson]

I tried this code:

use std::path::Path;

let path = Path::new("/foo/bar/baz/");
assert_eq!("/foo/bar/baz/", path.display().to_string());

let stripped_path = path.strip_prefix("/foo").unwrap();
println!("{}", stripped_path.display());

Expected output: bar/baz/ (input with the to-strip part removed)

Actual output: bar/baz (input with the to-strip part and the trailing slash removed)

Playground

This is particularly relevant when/if #142503 lands, which further surfaces that inconsistency: playground

Meta

Reproduces in the stable and nightly builds currently on playground: 1.90.0 and 1.93.0-nightly (2025-10-28 278a909).

[ChrisDenton]

This is a consequence of Path's normalization rules. See Path::components. Essentially trailing slashes don't exist in Path's model and most Path functions implicitly use the model. This isn't always wanted hence the new trailing_sep functions.

We could fix this for some functions, such as strip_prefix. But we have to be careful of documentation that promises any normalization and of course we would need to ensure test coverage to avoid regressions.

[MikkelPaulson]

Indeed, but the normalization rules are applied inconsistently. Either the trailing slash should be stripped immediately upon creating the Path, or it should be left unmodified throughout the lifecycle of the Path unless the trailing component is changed.

I understand and agree with the motivation behind trailing_sep, but with the current behaviour, these two snippets will produce different results:

// "bar/"
println!(
    "{}",
    Path::new("/foo/bar")
        .strip_prefix("/foo")
        .unwrap()
        .with_trailing_sep()
        .display(),
);

// "bar"
println!(
    "{}",
    Path::new("/foo/bar")
        .with_trailing_sep()
        .strip_prefix("/foo")
        .unwrap()
        .display(),
);

Playground

Digging around a bit, the problem is coming from (and also occurs in) Components::as_path(). When the Components iterator is new, as_path() returns the full input, but as soon as it is advanced, the trailing slash is dropped.

[MikkelPaulson]

If I were implementing this in greenfield today, I would include a Component::TrailingSep variant that occurs with zero length at the end of a Component stream, plus of course the methods for adding and stripping separators included in path_trailing_sep. /blah is not semantically the same as /blah/, and Rust agrees despite Path's promises of normalization:

// called `Result::unwrap()` on an `Err` value:
// Os { code: 20, kind: NotADirectory, message: "Not a directory" }
std::fs::read_to_string(Path::new("Cargo.toml/")).unwrap();

Rationalizing Path is a bigger job involving the possibility of breaking changes, but the strip_prefix()/as_path() issue is a clear bug that can be resolved without rocking the boat overmuch.