Make const Fn require const FnMut

Author: theemathas

library/core/src/ops/function.rs

@@ -73,7 +73,7 @@ use crate::marker::Tuple;
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
 #[rustc_const_unstable(feature = "const_trait_impl", issue = "143874")]
-pub const trait Fn<Args: Tuple>: FnMut<Args> {
+pub const trait Fn<Args: Tuple>: [const] FnMut<Args> {
     /// Performs the call operation.
     #[unstable(feature = "fn_traits", issue = "29625")]
     extern "rust-call" fn call(&self, args: Args) -> Self::Output;

tests/ui/traits/const-traits/call.rs

@@ -6,6 +6,7 @@
 pub const _: () = {
     assert!((const || true)());
     //~^ ERROR }: [const] Fn()` is not satisfied
+    //~| ERROR }: [const] FnMut()` is not satisfied
 };
 
 fn main() {}

tests/ui/traits/const-traits/call.stderr

@@ -4,6 +4,15 @@ error[E0277]: the trait bound `{closure@$DIR/call.rs:7:14: 7:22}: [const] Fn()`
 LL |     assert!((const || true)());
    |             ^^^^^^^^^^^^^^^^^
 
-error: aborting due to 1 previous error
+error[E0277]: the trait bound `{closure@$DIR/call.rs:7:14: 7:22}: [const] FnMut()` is not satisfied
+  --> $DIR/call.rs:7:13
+   |
+LL |     assert!((const || true)());
+   |             ^^^^^^^^^^^^^^^^^
+   |
+note: required by a bound in `call`
+  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/const-traits/const_closure-const_trait_impl-ice-113381.stderr

@@ -4,6 +4,15 @@ error[E0277]: the trait bound `{closure@$DIR/const_closure-const_trait_impl-ice-
 LL |     (const || (()).foo())();
    |     ^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 1 previous error
+error[E0277]: the trait bound `{closure@$DIR/const_closure-const_trait_impl-ice-113381.rs:15:6: 15:14}: [const] FnMut()` is not satisfied
+  --> $DIR/const_closure-const_trait_impl-ice-113381.rs:15:5
+   |
+LL |     (const || (()).foo())();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: required by a bound in `call`
+  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/const-traits/non-const-op-const-closure-non-const-outer.rs

@@ -12,4 +12,5 @@ impl Foo for () {
 fn main() {
     (const || { (()).foo() })();
     //~^ ERROR: }: [const] Fn()` is not satisfied
+    //~| ERROR: }: [const] FnMut()` is not satisfied
 }

tests/ui/traits/const-traits/non-const-op-const-closure-non-const-outer.stderr

@@ -4,6 +4,15 @@ error[E0277]: the trait bound `{closure@$DIR/non-const-op-const-closure-non-cons
 LL |     (const || { (()).foo() })();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 1 previous error
+error[E0277]: the trait bound `{closure@$DIR/non-const-op-const-closure-non-const-outer.rs:13:6: 13:14}: [const] FnMut()` is not satisfied
+  --> $DIR/non-const-op-const-closure-non-const-outer.rs:13:5
+   |
+LL |     (const || { (()).foo() })();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: required by a bound in `call`
+  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0277`.