Prove nested goals before const evaluation

compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs

@@ -1405,6 +1405,14 @@ where
         expected_term: I::Term,
         alias_const: ty::AliasConst<I>,
     ) -> QueryResultOrRerunNonErased<I> {
+        // Evaluation instantiates the constant's body with its arguments. An argument whose
+        // type does not match its parameter makes that body ill-formed, which CTFE cannot run.
+        self.try_evaluate_added_goals().inspect_err(|_| {
+            // Without recording the response here we attribute the error to this goal rather
+            // than to the nested goal which actually failed.
+            self.inspect.make_canonical_response(Certainty::Yes);
+        })?;
+
         match self.evaluate_const(param_env, alias_const)? {
             Some(evaluated) => {
                 self.eq(param_env, expected_term, evaluated.into())?;

tests/ui/const-generics/gca/mismatched-const-arg-type.rs

@@ -0,0 +1,55 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/156780>.
+
+//@ compile-flags: -Znext-solver
+
+#![feature(
+    generic_const_args,
+    generic_const_items,
+    macroless_generic_const_args,
+    min_generic_const_args
+)]
+#![expect(incomplete_features)]
+
+const F: f64 = 1.0;
+
+const ADD1<const N: usize>: usize = N + 1;
+
+const IGNORE<const N: usize>: usize = 0;
+
+trait Tr {
+    const C<const N: usize>: usize;
+}
+
+impl Tr for () {
+    const C<const N: usize>: usize = N + 1;
+}
+
+fn main() {
+    let _: [(); ADD1::<1f64>];
+    //~^ ERROR: the constant `1f64` is not of type `usize`
+    //~| ERROR: is not well-formed
+    let _: [(); ADD1::<1u8>];
+    //~^ ERROR: the constant `1` is not of type `usize`
+    //~| ERROR: is not well-formed
+    let _: [(); ADD1::<1i32>];
+    //~^ ERROR: the constant `1` is not of type `usize`
+    //~| ERROR: is not well-formed
+    let _: [(); ADD1::<true>];
+    //~^ ERROR: the constant `true` is not of type `usize`
+    //~| ERROR: is not well-formed
+    let _: [(); ADD1::<'a'>];
+    //~^ ERROR: the constant `'a'` is not of type `usize`
+    //~| ERROR: is not well-formed
+    let _: [(); ADD1::<"s">];
+    //~^ ERROR: the constant `"s"` is not of type `usize`
+    //~| ERROR: is not well-formed
+    let _: [(); ADD1::<F>];
+    //~^ ERROR: the constant `1f64` is not of type `usize`
+    //~| ERROR: is not well-formed
+    let _: [(); IGNORE::<1f64>];
+    //~^ ERROR: the constant `1f64` is not of type `usize`
+    //~| ERROR: is not well-formed
+    let _: [(); <() as Tr>::C::<1f64>];
+    //~^ ERROR: type mismatch resolving `<() as Tr>::C<1f64> == _`
+    //~| ERROR: is not well-formed
+}

tests/ui/const-generics/gca/mismatched-const-arg-type.stderr

@@ -0,0 +1,111 @@
+error: the constant `1f64` is not of type `usize`
+  --> $DIR/mismatched-const-arg-type.rs:28:12
+   |
+LL |     let _: [(); ADD1::<1f64>];
+   |            ^^^^^^^^^^^^^^^^^^ expected `usize`, found `f64`
+
+error: the constant `1` is not of type `usize`
+  --> $DIR/mismatched-const-arg-type.rs:31:12
+   |
+LL |     let _: [(); ADD1::<1u8>];
+   |            ^^^^^^^^^^^^^^^^^ expected `usize`, found `u8`
+
+error: the constant `1` is not of type `usize`
+  --> $DIR/mismatched-const-arg-type.rs:34:12
+   |
+LL |     let _: [(); ADD1::<1i32>];
+   |            ^^^^^^^^^^^^^^^^^^ expected `usize`, found `i32`
+
+error: the constant `true` is not of type `usize`
+  --> $DIR/mismatched-const-arg-type.rs:37:12
+   |
+LL |     let _: [(); ADD1::<true>];
+   |            ^^^^^^^^^^^^^^^^^^ expected `usize`, found `bool`
+
+error: the constant `'a'` is not of type `usize`
+  --> $DIR/mismatched-const-arg-type.rs:40:12
+   |
+LL |     let _: [(); ADD1::<'a'>];
+   |            ^^^^^^^^^^^^^^^^^ expected `usize`, found `char`
+
+error: the constant `"s"` is not of type `usize`
+  --> $DIR/mismatched-const-arg-type.rs:43:12
+   |
+LL |     let _: [(); ADD1::<"s">];
+   |            ^^^^^^^^^^^^^^^^^ expected `usize`, found `&'static str`
+
+error: the constant `1f64` is not of type `usize`
+  --> $DIR/mismatched-const-arg-type.rs:46:12
+   |
+LL |     let _: [(); ADD1::<F>];
+   |            ^^^^^^^^^^^^^^^ expected `usize`, found `f64`
+
+error: the constant `1f64` is not of type `usize`
+  --> $DIR/mismatched-const-arg-type.rs:49:12
+   |
+LL |     let _: [(); IGNORE::<1f64>];
+   |            ^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `f64`
+
+error[E0271]: type mismatch resolving `<() as Tr>::C<1f64> == _`
+  --> $DIR/mismatched-const-arg-type.rs:52:12
+   |
+LL |     let _: [(); <() as Tr>::C::<1f64>];
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ
+
+error: the type `[(); ADD1::<1f64>]` is not well-formed
+  --> $DIR/mismatched-const-arg-type.rs:28:12
+   |
+LL |     let _: [(); ADD1::<1f64>];
+   |            ^^^^^^^^^^^^^^^^^^
+
+error: the type `[(); ADD1::<1>]` is not well-formed
+  --> $DIR/mismatched-const-arg-type.rs:31:12
+   |
+LL |     let _: [(); ADD1::<1u8>];
+   |            ^^^^^^^^^^^^^^^^^
+
+error: the type `[(); ADD1::<1>]` is not well-formed
+  --> $DIR/mismatched-const-arg-type.rs:34:12
+   |
+LL |     let _: [(); ADD1::<1i32>];
+   |            ^^^^^^^^^^^^^^^^^^
+
+error: the type `[(); ADD1::<true>]` is not well-formed
+  --> $DIR/mismatched-const-arg-type.rs:37:12
+   |
+LL |     let _: [(); ADD1::<true>];
+   |            ^^^^^^^^^^^^^^^^^^
+
+error: the type `[(); ADD1::<'a'>]` is not well-formed
+  --> $DIR/mismatched-const-arg-type.rs:40:12
+   |
+LL |     let _: [(); ADD1::<'a'>];
+   |            ^^^^^^^^^^^^^^^^^
+
+error: the type `[(); ADD1::<"s">]` is not well-formed
+  --> $DIR/mismatched-const-arg-type.rs:43:12
+   |
+LL |     let _: [(); ADD1::<"s">];
+   |            ^^^^^^^^^^^^^^^^^
+
+error: the type `[(); ADD1::<1f64>]` is not well-formed
+  --> $DIR/mismatched-const-arg-type.rs:46:12
+   |
+LL |     let _: [(); ADD1::<F>];
+   |            ^^^^^^^^^^^^^^^
+
+error: the type `[(); IGNORE::<1f64>]` is not well-formed
+  --> $DIR/mismatched-const-arg-type.rs:49:12
+   |
+LL |     let _: [(); IGNORE::<1f64>];
+   |            ^^^^^^^^^^^^^^^^^^^^
+
+error: the type `[(); <() as Tr>::C::<1f64>]` is not well-formed
+  --> $DIR/mismatched-const-arg-type.rs:52:12
+   |
+LL |     let _: [(); <() as Tr>::C::<1f64>];
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 18 previous errors
+
+For more information about this error, try `rustc --explain E0271`.