Rollup merge of rust-lang#102273 - woppopo:relax_const_bound, r=fee1-dead

Allow `~const` bounds on non-const functions

Makes the behavior of bound of trait-associated functions and non-associated functions consistent.

Author: fee1-dead

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1415,7 +1415,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     if !self.is_tilde_const_allowed {
                         self.err_handler()
                             .struct_span_err(bound.span(), "`~const` is not allowed here")
-                            .note("only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions")
+                            .note("only allowed on bounds on functions, traits' associated types and functions, const impls and its associated functions")
                             .emit();
                     }
                 }
@@ -1523,9 +1523,8 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             });
         }
 
-        let tilde_const_allowed =
-            matches!(fk.header(), Some(FnHeader { constness: Const::Yes(_), .. }))
-                || matches!(fk.ctxt(), Some(FnCtxt::Assoc(_)));
+        let tilde_const_allowed = matches!(fk.header(), Some(FnHeader { .. }))
+            || matches!(fk.ctxt(), Some(FnCtxt::Assoc(_)));
 
         self.with_tilde_const(tilde_const_allowed, |this| visit::walk_fn(this, fk));
     }

src/test/ui/rfc-2632-const-trait-impl/tilde-const-and-const-params.rs

@@ -0,0 +1,34 @@
+// check-pass
+#![feature(const_trait_impl)]
+#![feature(generic_arg_infer)]
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+struct Foo<const N: usize>;
+
+impl<const N: usize> Foo<N> {
+   fn add<A: ~const Add42>(self) -> Foo<{ A::add(N) }> {
+      Foo
+   }
+}
+
+#[const_trait]
+trait Add42 {
+    fn add(a: usize) -> usize;
+}
+
+impl const Add42 for () {
+    fn add(a: usize) -> usize {
+        a + 42
+    }
+}
+
+fn bar<A: ~const Add42, const N: usize>(_: Foo<N>) -> Foo<{ A::add(N) }> {
+    Foo
+}
+
+fn main() {
+   let foo = Foo::<0>;
+   let foo = bar::<(), _>(foo);
+   let _foo = bar::<(), _>(foo);
+}

src/test/ui/rfc-2632-const-trait-impl/tilde-const-invalid-places.rs

@@ -17,12 +17,6 @@ fn rpit_assoc_bound() -> impl IntoIterator<Item: ~const T> { Some(S) }
 fn apit_assoc_bound(_: impl IntoIterator<Item: ~const T>) {}
 //~^ ERROR `~const` is not allowed
 
-fn generic<P: ~const T>() {}
-//~^ ERROR `~const` is not allowed
-
-fn where_clause<P>() where P: ~const T {}
-//~^ ERROR `~const` is not allowed
-
 struct TildeQuestion<T: ~const ?Sized>(std::marker::PhantomData<T>);
 //~^ ERROR `~const` and `?` are mutually exclusive
 

src/test/ui/rfc-2632-const-trait-impl/tilde-const-invalid-places.stderr

@@ -4,53 +4,37 @@ error: `~const` is not allowed here
 LL | fn rpit() -> impl ~const T { S }
    |                   ^^^^^^^^
    |
-   = note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions
+   = note: only allowed on bounds on functions, traits' associated types and functions, const impls and its associated functions
 
 error: `~const` is not allowed here
   --> $DIR/tilde-const-invalid-places.rs:11:17
    |
 LL | fn apit(_: impl ~const T) {}
    |                 ^^^^^^^^
    |
-   = note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions
+   = note: only allowed on bounds on functions, traits' associated types and functions, const impls and its associated functions
 
 error: `~const` is not allowed here
   --> $DIR/tilde-const-invalid-places.rs:14:50
    |
 LL | fn rpit_assoc_bound() -> impl IntoIterator<Item: ~const T> { Some(S) }
    |                                                  ^^^^^^^^
    |
-   = note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions
+   = note: only allowed on bounds on functions, traits' associated types and functions, const impls and its associated functions
 
 error: `~const` is not allowed here
   --> $DIR/tilde-const-invalid-places.rs:17:48
    |
 LL | fn apit_assoc_bound(_: impl IntoIterator<Item: ~const T>) {}
    |                                                ^^^^^^^^
    |
-   = note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions
-
-error: `~const` is not allowed here
-  --> $DIR/tilde-const-invalid-places.rs:20:15
-   |
-LL | fn generic<P: ~const T>() {}
-   |               ^^^^^^^^
-   |
-   = note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions
-
-error: `~const` is not allowed here
-  --> $DIR/tilde-const-invalid-places.rs:23:31
-   |
-LL | fn where_clause<P>() where P: ~const T {}
-   |                               ^^^^^^^^
-   |
-   = note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions
+   = note: only allowed on bounds on functions, traits' associated types and functions, const impls and its associated functions
 
 error: `~const` and `?` are mutually exclusive
-  --> $DIR/tilde-const-invalid-places.rs:26:25
+  --> $DIR/tilde-const-invalid-places.rs:20:25
    |
 LL | struct TildeQuestion<T: ~const ?Sized>(std::marker::PhantomData<T>);
    |                         ^^^^^^^^^^^^^
 
-error: aborting due to 7 previous errors
+error: aborting due to 5 previous errors