mGCA: Validate const literal against expected type by reddevilmidzy · Pull Request #152001 · rust-lang/rust

reddevilmidzy · 2026-02-02T16:10:33Z

also fix: #133966 (moved crashes test)

tests/ui/const-generics/mgca/literal-type-mismatch.rs

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

BoxyUwU · 2026-02-04T12:44:13Z

very cool :) thanks for working on this

…=oli-obk Dont strip const blocks in array lengths r? oli-obk mGCA now handles const blocks by *always* handling them during `lower_expr_to_const_arg_direct` instead of *sometimes* stripping them out at parse time. This is just generally a lot clearer/nicer but also means parsing isn't lossy which is just straight up wrong. We now use `MgcaDisambiguation::Direct` for const blocks because we "directly" represent a const block as `hir::ConstArgKind::Anon` :> The only time that an anon const for const generics uses `MgcaDisambiguation::AnonConst` is for unbraced literals. Once we properly support literals in `hir::ConstArgKind` (see rust-lang#152139 rust-lang#152001) then `MgcaDisambiguation` can be renamed to `AnonConstKind` with `TypeSystem` and `NonTypeSystem` variants. We can also get rid of `mgca_direct_lit_hack`. I expect this to be a very nice cleanup :) Fixes rust-lang/rustfmt#6788 The diff relating to passing spans around is to avoid a bunch of mGCA diagnostics changing from `const {}` to `{}`. I'm not entirely sure why this was happening. cc @rust-lang/rustfmt How do I run the tests in the rustfmt repo from here? `x test rustfmt` only seems to run like 100 tests and doesn't result in a `target/issue-6788.rs` getting created. I've verified locally that this formats correctly though

Rollup merge of #152234 - BoxyUwU:dont_strip_const_blocks, r=oli-obk Dont strip const blocks in array lengths r? oli-obk mGCA now handles const blocks by *always* handling them during `lower_expr_to_const_arg_direct` instead of *sometimes* stripping them out at parse time. This is just generally a lot clearer/nicer but also means parsing isn't lossy which is just straight up wrong. We now use `MgcaDisambiguation::Direct` for const blocks because we "directly" represent a const block as `hir::ConstArgKind::Anon` :> The only time that an anon const for const generics uses `MgcaDisambiguation::AnonConst` is for unbraced literals. Once we properly support literals in `hir::ConstArgKind` (see #152139 #152001) then `MgcaDisambiguation` can be renamed to `AnonConstKind` with `TypeSystem` and `NonTypeSystem` variants. We can also get rid of `mgca_direct_lit_hack`. I expect this to be a very nice cleanup :) Fixes rust-lang/rustfmt#6788 The diff relating to passing spans around is to avoid a bunch of mGCA diagnostics changing from `const {}` to `{}`. I'm not entirely sure why this was happening. cc @rust-lang/rustfmt How do I run the tests in the rustfmt repo from here? `x test rustfmt` only seems to run like 100 tests and doesn't result in a `target/issue-6788.rs` getting created. I've verified locally that this formats correctly though

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

compiler/rustc_mir_build/src/thir/constant.rs

reddevilmidzy · 2026-02-07T12:19:39Z

Haha, ICE occurs in other tests...

reddevilmidzy

Thanks for your quick review. 😊

View changes since this review

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

tests/ui/const-generics/mgca/type_const-mismatched-types.rs

reddevilmidzy

In ten crash tests, the ICE disappeared; however, in ‎tests/crashes/117460.rs, tests/crashes/114212-2.rs and tests/crashes/114212.rs, adding the main function caused the ICE to occur again.

View changes since this review

reddevilmidzy · 2026-02-08T09:12:14Z

tests/ui/const-generics/generic_const_exprs/enum-const-generic-default-param.rs

@@ -0,0 +1,23 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/116554>


This issue was closed; is there a need to add further testing?

unsure, I will look over all the GCE tests (outside of this PR) at some point soon and see which ones are worth keeping

tests/crashes/101036.rs

reddevilmidzy · 2026-02-08T09:35:23Z

Could the following issues also be closed? 🤔

#119824
#133966
#136416

already closed
#94846
#106473
#116554

reddevilmidzy · 2026-02-11T05:18:48Z

tests/ui/const-generics/generic_const_exprs/lit_type_mismatch.rs

Removed tests related to generic_const_args that were causing crashes.

reddevilmidzy · 2026-02-11T05:20:20Z

tests/ui/const-generics/mgca/nonsensical-negated-literal.rs

+    foo::<{ Foo { field: -1_usize } }>();
+    //~^ ERROR: type annotations needed for the literal
+    foo::<{ Foo { field: { -1_usize } } }>();
+    //~^ ERROR: complex const arguments must be placed inside of a `const` block
+    foo::<{ Foo { field: -true } }>();
+    //~^ ERROR: the constant `true` is not of type `isize`
+    foo::<{ Foo { field: { -true } } }>();
+    //~^ ERROR: complex const arguments must be placed inside of a `const` block
+    foo::<{ Foo { field: -"<3" } }>();
+    //~^ ERROR: the constant `"<3"` is not of type `isize`
+    foo::<{ Foo { field: { -"<3" } } }>();
+    //~^ ERROR: complex const arguments must be placed inside of a `const` block


Added the test mentioned in #152139.

rustbot · 2026-02-11T06:44:13Z

HIR ty lowering was modified

cc @fmease

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

Some changes occurred in match checking

cc @Nadrieril

Some changes occurred in rustc_ty_utils::consts.rs

cc @BoxyUwU

RalfJung · 2026-02-11T07:37:52Z

compiler/rustc_middle/src/mir/interpret/mod.rs

    pub neg: bool,
 }

+pub fn const_lit_matches_ty<'tcx>(


This does not seem like a great place for this function -- it doesn't really have anything to do with the interpreter, does it?

I guess you put it next to LitToConstInput, but that type also doesn't belong here either IMO. It has very little to do with everything else in this module.

Oh, yes, I placed it here to place it in the same place as LitToConstInput.
I'll look for something more meaningful! LitToConstInput too.

I created rustc_middle/src/ty/consts/lit.rs and moved it there. Does it look okay?

4f93ae7

that seems ok to me, we might wind up getting more logic for this as mGCA progresses so seems nice to have a module 🤔

compiler/rustc_mir_build/src/thir/pattern/mod.rs

Co-authored-by: Boxy <rust@boxyuwu.dev>

…eneric_const_exprs/lit_type_mismatch.rs

Relocate LitToConstInput and const_lit_matches_ty from mir::interpret to ty::consts::lit

BoxyUwU · 2026-02-14T10:39:58Z

tests/ui/const-generics/mgca/nonsensical-negated-literal.rs

+    foo::<{ Foo { field: -1_usize } }>();
+    //~^ ERROR: type annotations needed for the literal
+    foo::<{ Foo { field: { -1_usize } } }>();
+    //~^ ERROR: complex const arguments must be placed inside of a `const` block


This error message implies we handle negated literals incorrectly during ast lowering I think. lower_expr_to_const_arg_direct is presumably not handling { -1_usize } even though it should (I think probably there is no reason for the arm for blocks to match on what kind of expr is being wrapped).

If you'd be interested, once this PR lands would you be interested in fixing that and #152246 in a followup PR?

I think we probably also handle fn foo<const F: &str>() { foo::<{ -"hi" }>(); } wrong (i.e. we accept it?). I think this is also a problem with ast lowering and we should be checking there that the literal is an integer. Could also do that in a followup PR if you like?

Yes, I'd be happy to work on that in a follow-up PR! I'll take a closer look at the AST lowering behavior you mentioned.

BoxyUwU · 2026-02-14T10:51:09Z

@bors r+

rust-bors · 2026-02-14T10:51:12Z

📌 Commit 01d48c6 has been approved by BoxyUwU

It is now in the queue for this repository.

mGCA: Validate const literal against expected type close: rust-lang#151625 close: rust-lang#150983 also fix: rust-lang#133966 (moved crashes test)

…uwer Rollup of 7 pull requests Successful merges: - #152001 (mGCA: Validate const literal against expected type) - #152120 (Don't ICE on layout error in vtable computation) - #152512 (core: Implement feature `float_exact_integer_constants`) - #152531 (`proc_macro::bridge`: simplify `ExecutionStrategy` and `DispatcherTrait`) - #152577 (Port #[rustc_proc_macro_decls] to the new attribute parser.) - #152590 (DepGraphQuery: correctly skip adding edges with not-yet-added nodes) - #152612 (Rename `inline_fluent!` to `msg!`)

…uwer Rollup of 8 pull requests Successful merges: - #152618 (stdarch subtree update) - #152001 (mGCA: Validate const literal against expected type) - #152120 (Don't ICE on layout error in vtable computation) - #152531 (`proc_macro::bridge`: simplify `ExecutionStrategy` and `DispatcherTrait`) - #152577 (Port #[rustc_proc_macro_decls] to the new attribute parser.) - #152570 (Port #[rustc_test_marker] to the attribute parser) - #152590 (DepGraphQuery: correctly skip adding edges with not-yet-added nodes) - #152612 (Rename `inline_fluent!` to `msg!`)

Rollup merge of #152001 - reddevilmidzy:mgca-i, r=BoxyUwU mGCA: Validate const literal against expected type close: #151625 close: #150983 also fix: #133966 (moved crashes test)

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Feb 2, 2026

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mGCA: Support directly represented negated literals #152123

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khyperia mentioned this pull request Feb 6, 2026

mGCA: Support directly represented negated literals #152139

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Dont strip const blocks in array lengths #152234

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mGCA: remove parser special case for literals #152246

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reddevilmidzy marked this pull request as ready for review February 11, 2026 06:44

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reddevilmidzy and others added 3 commits February 14, 2026 04:12

mGCA: Validate const literal against expected type

8af02e2

Co-authored-by: Boxy <rust@boxyuwu.dev>

modify error comment and bless test, delete tests/ui/const-generics/g…

b4ee995

…eneric_const_exprs/lit_type_mismatch.rs

Move LitToConstInput into ty::consts

01d48c6

Relocate LitToConstInput and const_lit_matches_ty from mir::interpret to ty::consts::lit

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Rollup of 5 pull requests #152614

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Rollup of 7 pull requests #152616

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Rollup of 8 pull requests #152627

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Unrolled build for #152001

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Rollup merge of #152001 - reddevilmidzy:mgca-i, r=BoxyUwU mGCA: Validate const literal against expected type close: #151625 close: #150983 also fix: #133966 (moved crashes test)

reddevilmidzy deleted the mgca-i branch February 15, 2026 00:41

matthiaskrgr mentioned this pull request Feb 15, 2026

[ICE]: Binder / Cond<UnevaluatedConst has parameters, but no args were provided in instantiate #152647

Open

		@@ -0,0 +1,23 @@
		//! Regression test for <https://github.com/rust-lang/rust/issues/116554>

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