fallback to provided signature in the event of a type error

This prevents regressions on some annoying cases.

src/test/compile-fail/closure-expected-type/expect-fn-supply-fn.rs

@@ -40,14 +40,14 @@ fn expect_free_supply_bound() {
     // Here, we are given a function whose region is bound at closure level,
     // but we expect one bound in the argument. Error results.
     with_closure_expecting_fn_with_free_region(|x: fn(&u32), y| {});
-    //~^ ERROR mismatched types
+    //~^ ERROR type mismatch in closure arguments
 }
 
 fn expect_bound_supply_free_from_fn<'x>(x: &'x u32) {
     // Here, we are given a `fn(&u32)` but we expect a `fn(&'x
     // u32)`. In principle, this could be ok, but we demand equality.
     with_closure_expecting_fn_with_bound_region(|x: fn(&'x u32), y| {});
-    //~^ ERROR mismatched types
+    //~^ ERROR type mismatch in closure arguments
 }
 
 fn expect_bound_supply_free_from_closure() {
@@ -56,7 +56,7 @@ fn expect_bound_supply_free_from_closure() {
     // the argument level.
     type Foo<'a> = fn(&'a u32);
     with_closure_expecting_fn_with_bound_region(|_x: Foo<'_>, y| {});
-    //~^ ERROR mismatched types
+    //~^ ERROR type mismatch in closure arguments
 }
 
 fn expect_bound_supply_bound<'x>(x: &'x u32) {

src/test/compile-fail/closure-expected-type/expect-infer-var-appearing-twice.rs

@@ -22,7 +22,7 @@ fn a() {
 fn b() {
     // Here we take the supplied types, resulting in an error later on.
     with_closure(|x: u32, y: i32| {
-        //~^ ERROR mismatched types
+        //~^ ERROR type mismatch in closure arguments
     });
 }
 

src/test/ui/mismatched_types/closure-arg-count.stderr

@@ -14,23 +14,6 @@ error[E0593]: closure is expected to take 2 arguments, but it takes 1 argument
    |               |
    |               expected closure that takes 2 arguments
 
-error: non-reference pattern used to match a reference (see issue #42640)
-  --> $DIR/closure-arg-count.rs:17:24
-   |
-17 |     [1, 2, 3].sort_by(|(tuple, tuple2)| panic!());
-   |                        ^^^^^^^^^^^^^^^ help: consider using: `&(tuple, tuple2)`
-   |
-   = help: add #![feature(match_default_bindings)] to the crate attributes to enable
-
-error[E0308]: mismatched types
-  --> $DIR/closure-arg-count.rs:17:24
-   |
-17 |     [1, 2, 3].sort_by(|(tuple, tuple2)| panic!());
-   |                        ^^^^^^^^^^^^^^^ expected integral variable, found tuple
-   |
-   = note: expected type `{integer}`
-              found type `(_, _)`
-
 error[E0593]: closure is expected to take 2 arguments, but it takes 1 argument
   --> $DIR/closure-arg-count.rs:17:15
    |
@@ -73,5 +56,5 @@ error[E0593]: closure is expected to take a single 2-tuple as argument, but it t
    |                                                     |
    |                                                     expected closure that takes a single 2-tuple as argument
 
-error: aborting due to 9 previous errors
+error: aborting due to 7 previous errors