hir ty lower

Author: BoxyUwU

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -2486,16 +2486,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let expr = &tcx.hir_body(anon.body).value;
         debug!(?expr);
 
-        // If the rhs is an anon const naming generics it shouldn't have
-        // access to then we lower to `ConstKind::Error`. This prevents
-        // `try_lower_anon_const_lit` from ICEing on anon consts such as
-        // `const { N }` which aren't supposed to be legal.
-        if let ty::AnonConstKind::MCG = tcx.anon_const_kind(anon.def_id)
-            && let Err(e) = tcx.check_anon_const_invalid_param_uses(anon.def_id)
-        {
-            return ty::Const::new_error(tcx, e);
-        }
-
         // FIXME(generic_const_parameter_types): We should use the proper generic args
         // here. It's only used as a hint for literals so doesn't matter too much to use the right
         // generic arguments, just weaker type inference.
@@ -2521,24 +2511,27 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     ) -> Option<Const<'tcx>> {
         let tcx = self.tcx();
 
-        // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
-        // currently have to be wrapped in curly brackets, so it's necessary to special-case.
+        // Unwrap a block, so that e.g. `{ 1 }` is recognised as a literal. This makes the
+        // performance optimisation of directly lowering anon consts occur more often.
         let expr = match &expr.kind {
             hir::ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
                 block.expr.as_ref().unwrap()
             }
             _ => expr,
         };
 
+        // FIXME(mgca): remove this delayed bug once we start checking this
+        // when lowering `Ty/ConstKind::Param`s more generally.
         if let hir::ExprKind::Path(hir::QPath::Resolved(
             _,
             &hir::Path { res: Res::Def(DefKind::ConstParam, _), .. },
         )) = expr.kind
         {
-            span_bug!(
+            let e = tcx.dcx().span_delayed_bug(
                 expr.span,
-                "try_lower_anon_const_lit: received const param which shouldn't be possible"
+                "try_lower_anon_const_lit: received const param which shouldn't be possible",
             );
+            return Some(ty::Const::new_error(tcx, e));
         };
 
         let lit_input = match expr.kind {

tests/crashes/127972.rs

@@ -33,7 +33,6 @@ fn bar<T: Trait, const N: u32>() {
     // in anon const const args
     foo::<{ Some::<u32> { 0: const { N + 1 } } }>();
     //~^ ERROR: generic parameters may not be used in const operations
-    //~| ERROR: generic parameters may not be used in const operations
 }
 
 fn main() {}

tests/crashes/137888.rs

@@ -10,13 +10,5 @@ error: generic parameters may not be used in const operations
 LL |     foo::<{ Some::<u32> { 0: const { N + 1 } } }>();
    |                                      ^
 
-error: generic parameters may not be used in const operations
-  --> $DIR/adt_expr_arg_simple.rs:34:38
-   |
-LL |     foo::<{ Some::<u32> { 0: const { N + 1 } } }>();
-   |                                      ^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 

tests/crashes/140275.rs

@@ -0,0 +1,10 @@
+#![feature(associated_const_equality, generic_const_items, min_generic_const_args)]
+#![expect(incomplete_features)]
+// library crates exercise weirder code paths around
+// DefIds which were created for const args.
+#![crate_type = "lib"]
+
+struct Foo<const N: usize>;
+
+type Alias<const N: usize> = Foo<const { N }>;
+//~^ ERROR: generic parameters may not be used in const operations

tests/ui/const-generics/mgca/adt_expr_arg_simple.rs

@@ -0,0 +1,8 @@
+error: generic parameters may not be used in const operations
+  --> $DIR/explicit_anon_consts-2.rs:9:42
+   |
+LL | type Alias<const N: usize> = Foo<const { N }>;
+   |                                          ^
+
+error: aborting due to 1 previous error
+

tests/ui/const-generics/mgca/adt_expr_arg_simple.stderr

@@ -0,0 +1,10 @@
+#![feature(associated_const_equality, generic_const_items, min_generic_const_args)]
+#![expect(incomplete_features)]
+// library crates exercise weirder code paths around
+// DefIds which were created for const args.
+#![crate_type = "lib"]
+
+struct Foo<const N: usize>;
+
+type Alias<const N: usize> = [(); const { N }];
+//~^ ERROR: generic parameters may not be used in const operations

tests/ui/const-generics/mgca/explicit_anon_consts-2.rs

@@ -0,0 +1,8 @@
+error: generic parameters may not be used in const operations
+  --> $DIR/explicit_anon_consts-3.rs:9:43
+   |
+LL | type Alias<const N: usize> = [(); const { N }];
+   |                                           ^
+
+error: aborting due to 1 previous error
+