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Rollup merge of #140159 - thaliaarchi:pathbuf-extension, r=workingjubilee

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Avoid redundant WTF-8 checks in `PathBuf`

Eliminate checks for WTF-8 boundaries in `PathBuf::set_extension` and `add_extension`, where joining WTF-8 surrogate halves is impossible. Don't convert the `str` to `OsStr`, because `OsString::push` specializes to skip the joining when given strings.

To assist in this, mark the internal methods `OsString::truncate` and `extend_from_slice` as `unsafe` to communicate their safety invariants better than with module privacy.

Similar to #137777.

cc `@joboet` `@ChrisDenton`
This commit is contained in:
Stuart Cook
2025-05-02 22:17:00 +10:00
committed by GitHub
parent 6fc78d410d 0f0c0d8b16
commit 5a58c7a6ab
4 changed files with 63 additions and 29 deletions
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19
library/std/src/path.rs
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@@ -1529,11 +1529,13 @@ impl PathBuf {
self.inner.truncate(end_file_stem.wrapping_sub(start));
// add the new extension, if any
let new = extension;
let new = extension.as_encoded_bytes();
if !new.is_empty() {
self.inner.reserve_exact(new.len() + 1);
self.inner.push(OsStr::new("."));
self.inner.push(new);
self.inner.push(".");
// SAFETY: Since a UTF-8 string was just pushed, it is not possible
// for the buffer to end with a surrogate half.
unsafe { self.inner.extend_from_slice_unchecked(new) };
}
true
@@ -1597,7 +1599,7 @@ impl PathBuf {
Some(f) => f.as_encoded_bytes(),
};
let new = extension;
let new = extension.as_encoded_bytes();
if !new.is_empty() {
// truncate until right after the file name
// this is necessary for trimming the trailing slash
@@ -1607,8 +1609,10 @@ impl PathBuf {
// append the new extension
self.inner.reserve_exact(new.len() + 1);
self.inner.push(OsStr::new("."));
self.inner.push(new);
self.inner.push(".");
// SAFETY: Since a UTF-8 string was just pushed, it is not possible
// for the buffer to end with a surrogate half.
unsafe { self.inner.extend_from_slice_unchecked(new) };
}
true
@@ -2769,7 +2773,8 @@ impl Path {
};
let mut new_path = PathBuf::with_capacity(new_capacity);
new_path.inner.extend_from_slice(slice_to_copy);
// SAFETY: The path is empty, so cannot have surrogate halves.
unsafe { new_path.inner.extend_from_slice_unchecked(slice_to_copy) };
new_path.set_extension(extension);
new_path
}