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Fix Ord, Eq and Hash implementation of panic::Location #144510

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Fix Ord, Eq and Hash implementation of panic::Location #144510

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40 changes: 39 additions & 1 deletion library/core/src/panic/location.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
use crate::cmp::Ordering;
use crate::ffi::CStr;
use crate::fmt;
use crate::hash::{Hash, Hasher};
use crate::marker::PhantomData;
use crate::ptr::NonNull;

Expand Down Expand Up @@ -32,7 +34,7 @@ use crate::ptr::NonNull;
/// Files are compared as strings, not `Path`, which could be unexpected.
/// See [`Location::file`]'s documentation for more discussion.
#[lang = "panic_location"]
#[derive(Copy, Clone, Eq, Hash, Ord, PartialEq, PartialOrd)]
#[derive(Copy, Clone)]
#[stable(feature = "panic_hooks", since = "1.10.0")]
pub struct Location<'a> {
// A raw pointer is used rather than a reference because the pointer is valid for one more byte
Expand All @@ -44,6 +46,42 @@ pub struct Location<'a> {
_filename: PhantomData<&'a str>,
}

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl PartialEq for Location<'_> {
fn eq(&self, other: &Self) -> bool {
self.file() == other.file() && self.line == other.line && self.col == other.col
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Is it worth flipping the order here? Comparing the filename is expensive, but in 99% of cases the line + column will mismatch on different locations I'd guess.

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@orlp orlp Jul 27, 2025 •
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I think that's fair enough for equality. What about the ordering? You could apply the same efficiency argument there although I think people would expect the ordering to be the filename > line > col.

EDIT: after double-checking the documentation, it very clearly states filename > line > col for both ordering and equality. However since that order isn't observable for equality I'll change this for efficiency.

}
}

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl Eq for Location<'_> {}

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl Ord for Location<'_> {
fn cmp(&self, other: &Self) -> Ordering {
self.file()
.cmp(other.file())
.then_with(|| self.line.cmp(&other.line))
.then_with(|| self.col.cmp(&other.col))
}
}

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl PartialOrd for Location<'_> {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
Some(self.cmp(other))
}
}

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl Hash for Location<'_> {
fn hash<H: Hasher>(&self, state: &mut H) {
self.file().hash(state);
self.line.hash(state);
self.col.hash(state);
}
}

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Can you add some test coverage for these? That would help prevent future accidental regressions.

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I'm actually not 100% sure if I can? In what little tests I've written for the standard library it's been single-file-per-test.

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You should be able to easily add some tests into library/coretests somewhere, I believe. Although you will need to have some sort of perma-unstable method to construct these that's marked #[doc(hidden)], since these are private fields.

#[stable(feature = "panic_hooks", since = "1.10.0")]
impl fmt::Debug for Location<'_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
Expand Down
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