Rollup merge of #164190 - estebank:fn-signatures, r=chenyukang

Tweak wording of "expected/found signature" errors

Do not incorrectly state that we expected a closure when we expected *anything* that conforms to an `Fn*` trait.

Author: jhpratt

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -3624,9 +3624,12 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             // Print type mismatch
             let (expected_args, given_args) = self.cmp(expected_ty, given_ty);
             err.note_expected_found(
-                "a closure with signature",
+                "type with signature",
                 expected_args,
-                "a closure with signature",
+                &format!(
+                    "{} with signature",
+                    trait_pred.self_ty().skip_binder().prefix_string(self.tcx)
+                ),
                 given_args,
             );
         }

library/core/src/ops/function.rs

@@ -67,8 +67,8 @@ use crate::ptr::NonNull;
         // SAFETY: tidy is not smart enough to tell that the below unsafe block is a string
         label = "call the function in a closure: `|| unsafe {{ /* code */ }}`"
     ),
-    message = "expected an `{This:resolved}` closure, found `{Self}`",
-    label = "expected an `{This:resolved}` closure, found `{Self}`"
+    message = "expected `{This:resolved}` signature, found `{Self}`",
+    label = "expected `{This:resolved}` signature, found `{Self}`"
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
@@ -154,8 +154,8 @@ pub const trait Fn<Args: Tuple>: [const] FnMut<Args> {
         // SAFETY: tidy is not smart enough to tell that the below unsafe block is a string
         label = "call the function in a closure: `|| unsafe {{ /* code */ }}`"
     ),
-    message = "expected an `{This:resolved}` closure, found `{Self}`",
-    label = "expected an `{This:resolved}` closure, found `{Self}`"
+    message = "expected `{This:resolved}` signature, found `{Self}`",
+    label = "expected `{This:resolved}` signature, found `{Self}`"
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
@@ -233,8 +233,8 @@ pub const trait FnMut<Args: Tuple>: FnOnce<Args> {
         // SAFETY: tidy is not smart enough to tell that the below unsafe block is a string
         label = "call the function in a closure: `|| unsafe {{ /* code */ }}`"
     ),
-    message = "expected an `{This:resolved}` closure, found `{Self}`",
-    label = "expected an `{This:resolved}` closure, found `{Self}`"
+    message = "expected `{This:resolved}` signature, found `{Self}`",
+    label = "expected `{This:resolved}` signature, found `{Self}`"
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]

tests/ui/abi/bad-custom.rs

@@ -142,7 +142,7 @@ async unsafe extern "custom" fn no_async_fn() {
 }
 
 fn no_promotion_to_fn_trait(f: unsafe extern "custom" fn()) -> impl Fn() {
-    //~^ ERROR expected an `Fn()` closure, found `unsafe extern "custom" fn()`
+    //~^ ERROR expected `Fn()` signature, found `unsafe extern "custom" fn()`
     f
 }
 

tests/ui/abi/bad-custom.stderr

@@ -418,7 +418,7 @@ LL | unsafe extern "custom" fn no_cold_attribute() {
    |        |
    |        `extern "custom"` because of this
 
-error[E0277]: expected an `Fn()` closure, found `unsafe extern "custom" fn()`
+error[E0277]: expected `Fn()` signature, found `unsafe extern "custom" fn()`
   --> $DIR/bad-custom.rs:144:64
    |
 LL | fn no_promotion_to_fn_trait(f: unsafe extern "custom" fn()) -> impl Fn() {

tests/ui/associated-types/normalization-ice-issue-149746.rs

@@ -4,14 +4,14 @@ trait Owner { type Ty<T: FnMut()>; }
 impl Owner for () { type Ty<T: FnMut()> = T; }
 pub struct Warns<T> {
     _significant_drop: <() as Owner>::Ty<T>,
-    //~^ ERROR expected an `FnMut()` closure, found `T`
+    //~^ ERROR expected `FnMut()` signature, found `T`
     field: String,
 }
 pub fn test<T>(w: Warns<T>) {
-    //~^ ERROR expected an `FnMut()` closure, found `T`
+    //~^ ERROR expected `FnMut()` signature, found `T`
     _ = || w.field
-    //~^ ERROR expected an `FnMut()` closure, found `T`
-    //~| ERROR expected an `FnMut()` closure, found `T`
+    //~^ ERROR expected `FnMut()` signature, found `T`
+    //~| ERROR expected `FnMut()` signature, found `T`
     //~| WARN: changes to closure capture in Rust 2021 will affect drop order
 }
 fn main() {}

tests/ui/associated-types/normalization-ice-issue-149746.stderr

@@ -1,8 +1,8 @@
-error[E0277]: expected an `FnMut()` closure, found `T`
+error[E0277]: expected `FnMut()` signature, found `T`
   --> $DIR/normalization-ice-issue-149746.rs:6:24
    |
 LL |     _significant_drop: <() as Owner>::Ty<T>,
-   |                        ^^^^^^^^^^^^^^^^^^^^ expected an `FnMut()` closure, found `T`
+   |                        ^^^^^^^^^^^^^^^^^^^^ expected `FnMut()` signature, found `T`
    |
    = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `Owner::Ty`
@@ -35,11 +35,11 @@ help: add a dummy let to cause `w` to be fully captured
 LL |     _ = || { let _ = &w; w.field }
    |            +++++++++++++         +
 
-error[E0277]: expected an `FnMut()` closure, found `T`
+error[E0277]: expected `FnMut()` signature, found `T`
   --> $DIR/normalization-ice-issue-149746.rs:12:9
    |
 LL |     _ = || w.field
-   |         ^^^^^^^^^^ expected an `FnMut()` closure, found `T`
+   |         ^^^^^^^^^^ expected `FnMut()` signature, found `T`
    |
    = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `Owner::Ty`
@@ -48,11 +48,11 @@ note: required by a bound in `Owner::Ty`
 LL | trait Owner { type Ty<T: FnMut()>; }
    |                          ^^^^^^^ required by this bound in `Owner::Ty`
 
-error[E0277]: expected an `FnMut()` closure, found `T`
+error[E0277]: expected `FnMut()` signature, found `T`
   --> $DIR/normalization-ice-issue-149746.rs:10:16
    |
 LL | pub fn test<T>(w: Warns<T>) {
-   |                ^ expected an `FnMut()` closure, found `T`
+   |                ^ expected `FnMut()` signature, found `T`
    |
    = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `Owner::Ty`
@@ -61,11 +61,11 @@ note: required by a bound in `Owner::Ty`
 LL | trait Owner { type Ty<T: FnMut()>; }
    |                          ^^^^^^^ required by this bound in `Owner::Ty`
 
-error[E0277]: expected an `FnMut()` closure, found `T`
+error[E0277]: expected `FnMut()` signature, found `T`
   --> $DIR/normalization-ice-issue-149746.rs:12:9
    |
 LL |     _ = || w.field
-   |         ^^^^^^^^^^ expected an `FnMut()` closure, found `T`
+   |         ^^^^^^^^^^ expected `FnMut()` signature, found `T`
    |
    = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
 note: required by a bound in `Owner::Ty`

tests/ui/async-await/async-fn/impl-header.rs

@@ -6,7 +6,7 @@ impl async Fn<()> for F {}
 //~^ ERROR `async` trait implementations are unsupported
 //~| ERROR the precise format of `Fn`-family traits' type parameters is subject to change
 //~| ERROR manual implementations of `Fn` are experimental
-//~| ERROR expected an `FnMut()` closure, found `F`
+//~| ERROR expected `FnMut()` signature, found `F`
 //~| ERROR not all trait items implemented, missing: `call`
 
 fn main() {}

tests/ui/async-await/async-fn/impl-header.stderr

@@ -30,11 +30,11 @@ LL | impl async Fn<()> for F {}
    |
    = help: implement the missing item: `fn call(&self, _: ()) -> <Self as FnOnce<()>>::Output { todo!() }` (unstable, requires feature `fn_traits`)
 
-error[E0277]: expected an `FnMut()` closure, found `F`
+error[E0277]: expected `FnMut()` signature, found `F`
   --> $DIR/impl-header.rs:5:23
    |
 LL | impl async Fn<()> for F {}
-   |                       ^ expected an `FnMut()` closure, found `F`
+   |                       ^ expected `FnMut()` signature, found `F`
    |
 help: the trait `FnMut()` is not implemented for `F`
   --> $DIR/impl-header.rs:3:1

tests/ui/cast/raw-ptr-to-dyn-fn-raw-ptr.rs

@@ -4,6 +4,6 @@ fn main() {
     let ptr: *mut () = core::ptr::null_mut();
     let _: &mut dyn Fn() = unsafe {
         &mut *(ptr as *mut dyn Fn())
-        //~^ ERROR expected an `Fn()` closure, found `()`
+        //~^ ERROR expected `Fn()` signature, found `()`
     };
 }

tests/ui/cast/raw-ptr-to-dyn-fn-raw-ptr.stderr

@@ -1,8 +1,8 @@
-error[E0277]: expected an `Fn()` closure, found `()`
+error[E0277]: expected `Fn()` signature, found `()`
   --> $DIR/raw-ptr-to-dyn-fn-raw-ptr.rs:6:16
    |
 LL |         &mut *(ptr as *mut dyn Fn())
-   |                ^^^ expected an `Fn()` closure, found `()`
+   |                ^^^ expected `Fn()` signature, found `()`
    |
    = help: the trait `Fn()` is not implemented for `()`
    = note: wrap the `()` in a closure with no arguments: `|| { /* code */ }`