Prevent ICE on ~const trait bounds involving non-const traits

Co-authored-by: Deadbeef <[email protected]>

Author: fmease

compiler/rustc_hir_analysis/src/astconv/generics.rs

@@ -262,7 +262,7 @@ pub fn create_args_for_parent_generic_args<'tcx, 'a>(
                             // impl const PartialEq for () {}
                             // ```
                             //
-                            // Since this is a const impl, we need to insert `<false>` at the end of
+                            // Since this is a const impl, we need to insert a host arg at the end of
                             // `PartialEq`'s generics, but this errors since `Rhs` isn't specified.
                             // To work around this, we infer all arguments until we reach the host param.
                             args.push(ctx.inferred_kind(Some(&args), param, infer_args));

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -378,7 +378,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             assert!(self_ty.is_none());
         }
 
-        let arg_count = check_generic_arg_count(
+        let mut arg_count = check_generic_arg_count(
             tcx,
             span,
             def_id,
@@ -390,6 +390,15 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             infer_args,
         );
 
+        if let ty::BoundConstness::ConstIfConst = constness
+            && generics.has_self
+            && !tcx.has_attr(def_id, sym::const_trait)
+        {
+            let reported = tcx.sess.emit_err(crate::errors::ConstBoundForNonConstTrait { span });
+            arg_count.correct =
+                Err(GenericArgCountMismatch { reported: Some(reported), invalid_args: vec![] });
+        }
+
         // Skip processing if type has no generic parameters.
         // Traits always have `Self` as a generic parameter, which means they will not return early
         // here and so associated type bindings will be handled regardless of whether there are any
@@ -570,13 +579,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             &mut args_ctx,
         );
 
-        if let ty::BoundConstness::ConstIfConst = constness
-            && generics.has_self
-            && !tcx.has_attr(def_id, sym::const_trait)
-        {
-            tcx.sess.emit_err(crate::errors::ConstBoundForNonConstTrait { span });
-        }
-
         (args, arg_count)
     }
 

tests/ui/rfcs/rfc-2632-const-trait-impl/tilde-const-on-non-const-trait.rs

@@ -0,0 +1,9 @@
+// Regression test for issue #117244.
+#![feature(const_trait_impl, effects)]
+
+trait NonConst {}
+
+const fn perform<T: ~const NonConst>() {}
+//~^ ERROR ~const can only be applied to `#[const_trait]` traits
+
+fn main() {}

tests/ui/rfcs/rfc-2632-const-trait-impl/tilde-const-on-non-const-trait.stderr

@@ -0,0 +1,8 @@
+error: ~const can only be applied to `#[const_trait]` traits
+  --> $DIR/tilde-const-on-non-const-trait.rs:6:28
+   |
+LL | const fn perform<T: ~const NonConst>() {}
+   |                            ^^^^^^^^
+
+error: aborting due to 1 previous error
+