fix: Error on illegal [const]s inside blocks within legal positions

Author: ShoyuVanilla

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1623,6 +1623,12 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             _ => self.with_in_trait_impl(None, |this| visit::walk_assoc_item(this, item, ctxt)),
         }
     }
+
+    fn visit_block(&mut self, block: &'a Block) {
+        // Conditional consts should not be used in invalid contexts—such as const bodies—even if
+        // they appear within the generic parameters of const traits or impls.
+        self.with_tilde_const(Some(TildeConstReason::Item), |this| visit::walk_block(this, block))
+    }
 }
 
 /// When encountering an equality constraint in a `where` clause, emit an error. If the code seems

tests/ui/traits/const-traits/conditionally-const-in-struct-args.rs

@@ -1,7 +1,3 @@
-//@ compile-flags: -Znext-solver
-//@ known-bug: #132067
-//@ check-pass
-
 #![feature(const_trait_impl)]
 
 struct S;
@@ -11,7 +7,11 @@ trait Trait<const N: u32> {}
 const fn f<
     T: Trait<
         {
+            const fn g<U: [const] Trait<0>>() {}
+
             struct I<U: [const] Trait<0>>(U);
+            //~^ ERROR `[const]` is not allowed here
+
             0
         },
     >,

tests/ui/traits/const-traits/conditionally-const-in-struct-args.stderr

@@ -0,0 +1,10 @@
+error: `[const]` is not allowed here
+  --> $DIR/conditionally-const-in-struct-args.rs:12:25
+   |
+LL |             struct I<U: [const] Trait<0>>(U);
+   |                         ^^^^^^^
+   |
+   = note: this item cannot have `[const]` trait bounds
+
+error: aborting due to 1 previous error
+