Start using pattern types in libcore #136006

oli-obk · 2025-01-24T16:24:51Z

blocked on rust-analyzer getting support for computing the right layout for pattern types

cc @Veykril no rush here, as long as we can't replace NonNull, there's no point in doing this change just yet

compiler-errors

Well r=me when/if it does get unblocked.

scottmcm · 2025-01-25T01:41:45Z

library/core/src/num/niche_types.rs

+        #[repr(transparent)]
+        $(#[$m])*
+        #[cfg(not(bootstrap))]
+        $vis struct $name(pattern_type!($int is $low..=$high));


Unsure: at least for the NonZeroBlahInner ones, it'd be nicer if these could just be type $name = pattern_type!($int is $low..=$high);, without the extra wrapper. Is that feasible, or are the trait implementations too far off?

(Relatedly, I'd love to be able to just derive traits on these again, particularly to not have to manually StructuralPartialEq.)

Yea... I wanna get there, but directly using pattern types is not a great experience at present

rustbot · 2025-01-27T09:38:22Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Veykril · 2025-01-27T09:54:06Z

Re rust-analyzer blocker, as it turns out to implement pattern types (to a degree that would unblock this) it comes down to the same architecture changes required as for rust-lang/rust-analyzer#7434 (which I am currently looking into), so that will take a bit.

rustbot · 2025-01-27T15:53:28Z

Some changes occurred to the CTFE machinery

cc @rust-lang/wg-const-eval

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

compiler/rustc_const_eval/src/interpret/validity.rs

oli-obk · 2025-03-11T11:50:38Z

Re rust-analyzer blocker, as it turns out to implement pattern types (to a degree that would unblock this) it comes down to the same architecture changes required as for rust-lang/rust-analyzer#7434 (which I am currently looking into), so that will take a bit.

@Veykril I think for the most part you could just treat pattern types opaquely and ignore the pattern's details. Casts to the base type don't require looking at the pattern and instantiating pattern types from literals could just be ignored by r-a and left to rustc. I don't think you actually need the layout of pattern types for anything else

compiler/rustc_hir_typeck/src/coercion.rs

library/core/src/num/niche_types.rs

programmerjake · 2025-03-11T16:38:07Z

library/core/src/num/niche_types.rs

        impl $name {
            #[inline]
            pub const fn new(val: $int) -> Option<Self> {
-                if (val as $uint) >= ($low as $uint) && (val as $uint) <= ($high as $uint) {
+                #[allow(non_contiguous_range_endpoints)]
+                if let $pat = val {
                    // SAFETY: just checked the inclusive range


Suggested change

// SAFETY: just checked the inclusive range

// SAFETY: just checked that the value matches the pattern

Veykril · 2025-03-12T05:57:04Z

Re rust-analyzer blocker, as it turns out to implement pattern types (to a degree that would unblock this) it comes down to the same architecture changes required as for rust-lang/rust-analyzer#7434 (which I am currently looking into), so that will take a bit.

@Veykril I think for the most part you could just treat pattern types opaquely and ignore the pattern's details. Casts to the base type don't require looking at the pattern and instantiating pattern types from literals could just be ignored by r-a and left to rustc. I don't think you actually need the layout of pattern types for anything else

But isn't the point of them that they have niches? If we treat them opaquely we won't see the niches of the type for layout calculation.

Either way I should be unblocked regarding rust-lang/rust-analyzer#7434 so I can start working on that again starting next week. Though if you want to get this merged and r-a is the remaining blocking reason we can work around it by special casing the relevant std/core type(s) if needed I think

oli-obk · 2025-03-12T06:30:27Z

But isn't the point of them that they have niches? If we treat them opaquely we won't see the niches of the type for layout calculation.

Ah then the sizes shown by ra would be wrong. Hmm I've never seem the sizes, didn't think about that

rustbot · 2025-03-13T12:39:10Z

The Miri subtree was changed

cc @rust-lang/miri

RalfJung · 2025-03-14T11:15:50Z

compiler/rustc_const_eval/src/interpret/call.rs

@@ -86,6 +86,9 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                let (_, field) = layout.non_1zst_field(self).unwrap();
                self.unfold_transparent(field, may_unfold)
            }
+            ty::Pat(base, _) => self.layout_of(*base).expect(


This should only be changed here if we also change the docs to guarantee that a pattern type is ABI-compatible with its inner type. And then the ABI compatibility tests should be extended to cover that (in the rustc test suite and the Miri test suite).

Well, considering it's the only way to guarantee that NonZeroU8 is still compatible with u8, I think the answer is yes, and that we already have at least tests for that. I'll add additional tests for bare pattern types

Please make a note on the tracking issue so that before stabilization, we decide whether this is true for all pattern types or only for some.

We unconditionally allow transmuting from pattern types to their base type. For any pattern. I don't see a design that could work differently

"A can be transmuted to B" does not imply "A and B are ABI-compatible". For instance, i32 and u32 are not ABI-compatible. The code you changed here is about Miri ensuring ABI compatibility of caller and callee.

RalfJung · 2025-03-14T11:18:16Z

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -70,6 +70,9 @@ pub(crate) fn eval_nullary_intrinsic<'tcx>(
            ty::Pat(_, pat) => match **pat {
                ty::PatternKind::Range { .. } => ConstValue::from_target_usize(0u64, &tcx),
                // Future pattern kinds may have more variants
+                // FIXME(pattern_types): make this report the number of distinct variants used in the
+                // or pattern in case the base type is an enum.
+                ty::PatternKind::Or(_) => ConstValue::from_target_usize(0_u64, &tcx),


Shouldn't there be a similar FIXME somewhere in codegen?

bors · 2025-03-15T12:19:37Z

☔ The latest upstream changes (presumably #138464) made this pull request unmergeable. Please resolve the merge conflicts.

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Test validity of pattern types #136145

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Allow const patterns of matches to contain pattern types

a464513

Prevent pattern type macro invocations from having trailing tokens

a38427e

Pull ast pattern type parsing out into a separate function

7693fc0

Directly generate TyPat instead of TyPatKind

c9d886e

Separate pattern lowering from pattern type lowering

a6cbf7a

Split out various pattern type matches into their own function

cb22e52

Add or-patterns to pattern types

9957a3c

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Start using pattern types in libcore

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Start using pattern types in libcore #136006

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bors commented Mar 15, 2025

	// SAFETY: just checked the inclusive range
	// SAFETY: just checked that the value matches the pattern

Start using pattern types in libcore #136006

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