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Merged
bors merged 4 commits into from
Mar 16, 2025
Merged

core: Make Debug impl of raw pointers print metadata if present #135080

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7176320
tests: Use `as *const _` instead of `.as_ptr()` in ptr fmt test
Enselic Jan 4, 2025
9479b6f
tests: Add regression test for `Debug` impl of raw pointers
Enselic Jan 3, 2025
d16da3b
core: Document why Pointee::Metadata can't have 'static bound
Enselic Feb 14, 2025
697737a
core: Make `Debug` impl of raw pointers print metadata if present
Enselic Jan 3, 2025
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core: Make Debug impl of raw pointers print metadata if present 
Make Rust pointers less magic by including metadata information in their
`Debug` output.

This does not break Rust stability guarantees because `Debug` output is
explicitly exempted from stability:
https://doc.rust-lang.org/std/fmt/trait.Debug.html#stability

Co-authored-by: Lukas <26522220+lukas-code@users.noreply.github.com>
Co-authored-by: Josh Stone <cuviper@gmail.com>
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@Enselic @lukas-code @cuviper
3 people committed Feb 15, 2025
commit 697737a8b18b685270f197ccdd1211e8a010b98b
9 changes: 8 additions & 1 deletion library/core/src/fmt/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2776,7 +2776,14 @@ impl Display for char {
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for *const T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
pointer_fmt_inner(self.expose_provenance(), f)
if <<T as core::ptr::Pointee>::Metadata as core::unit::IsUnit>::is_unit() {
pointer_fmt_inner(self.expose_provenance(), f)
} else {
f.debug_struct("Pointer")
.field_with("addr", |f| pointer_fmt_inner(self.expose_provenance(), f))
.field("metadata", &core::ptr::metadata(*self))
.finish()
}
}
}

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16 changes: 16 additions & 0 deletions library/core/src/unit.rs
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Expand Up @@ -17,3 +17,19 @@ impl FromIterator<()> for () {
iter.into_iter().for_each(|()| {})
}
}

pub(crate) trait IsUnit {
fn is_unit() -> bool;
}

impl<T: ?Sized> IsUnit for T {
default fn is_unit() -> bool {
false
}
}

impl IsUnit for () {
fn is_unit() -> bool {
true
}
}
8 changes: 4 additions & 4 deletions library/coretests/tests/fmt/mod.rs
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Expand Up @@ -42,12 +42,12 @@ fn test_fmt_debug_of_raw_pointers() {
check_fmt(plain as *const i32, "$HEX");

let slice = &mut [200, 300, 400][..];
check_fmt(slice as *mut [i32], "$HEX");
check_fmt(slice as *const [i32], "$HEX");
check_fmt(slice as *mut [i32], "Pointer { addr: $HEX, metadata: 3 }");
check_fmt(slice as *const [i32], "Pointer { addr: $HEX, metadata: 3 }");

let vtable = &mut 500 as &mut dyn Debug;
check_fmt(vtable as *mut dyn Debug, "$HEX");
check_fmt(vtable as *const dyn Debug, "$HEX");
check_fmt(vtable as *mut dyn Debug, "Pointer { addr: $HEX, metadata: DynMetadata($HEX) }");
check_fmt(vtable as *const dyn Debug, "Pointer { addr: $HEX, metadata: DynMetadata($HEX) }");
}

#[test]
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