Fix wrong report on closure args mismatch

when a ref is expected but not found.

Adds new error E0622

Fixes rust-lang#42143

src/librustc/diagnostics.rs

@@ -2027,4 +2027,5 @@ register_diagnostics! {
     E0495, // cannot infer an appropriate lifetime due to conflicting requirements
     E0566, // conflicting representation hints
     E0587, // conflicting packed and align representation hints
+    E0622, // type mismatch in closure arguments
 }

src/librustc/traits/error_reporting.rs

@@ -725,32 +725,27 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                                    expected_found.found,
                                                    expected_trait_ty.is_closure())
                 } else if let &TypeError::Sorts(ref expected_found) = e {
-                    let expected = if let ty::TyTuple(tys, _) = expected_found.expected.sty {
-                        tys.len()
-                    } else {
-                        1
-                    };
-                    let found = if let ty::TyTuple(tys, _) = expected_found.found.sty {
-                        tys.len()
-                    } else {
-                        1
-                    };
-
-                    if expected != found {
-                        // Expected `|| { }`, found `|x, y| { }`
-                        // Expected `fn(x) -> ()`, found `|| { }`
-                        self.report_arg_count_mismatch(span,
-                                                       found_span,
-                                                       expected,
-                                                       found,
-                                                       expected_trait_ty.is_closure())
+                    let mut count_mismatch = None;
+                    if let ty::TyTuple(expected_tys, _) = expected_found.expected.sty {
+                        if let ty::TyTuple(found_tys, _) = expected_found.found.sty {
+                            if expected_tys.len() != found_tys.len() { 
+                                // Expected `|| { }`, found `|x, y| { }`
+                                // Expected `fn(x) -> ()`, found `|| { }`
+                                count_mismatch = Some(self.report_arg_count_mismatch(span,
+                                                               found_span,
+                                                               expected_tys.len(),
+                                                               found_tys.len(),
+                                                               expected_trait_ty.is_closure()));
+                            }
+                        }
+                    }
+                    if let Some(count_mismatch) = count_mismatch {
+                        count_mismatch
                     } else {
-                        self.report_type_argument_mismatch(span,
-                                                            found_span,
-                                                            expected_trait_ty,
-                                                            expected_trait_ref,
-                                                            actual_trait_ref,
-                                                            e)
+                       self.report_closure_arg_mismatch(span,
+                                                         found_span,
+                                                         expected_trait_ref,
+                                                         actual_trait_ref) 
                     }
                 } else {
                     self.report_type_argument_mismatch(span,
@@ -825,6 +820,25 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         }
         err
     }
+
+    fn report_closure_arg_mismatch(&self,
+                           span: Span,
+                           found_span: Option<Span>,
+                           expected_ref: ty::PolyTraitRef<'tcx>,
+                           found: ty::PolyTraitRef<'tcx>)
+        -> DiagnosticBuilder<'tcx>
+    {
+        let mut err = struct_span_err!(self.tcx.sess, span, E0622,
+            "type mismatch in closure arguments");
+        if let Some(sp) = found_span {
+            err.span_label(span, format!("expected closure that takes a `{}`", found));
+            err.span_label(sp, format!("takes a `{}`", expected_ref));
+        } else {
+            panic!();
+        }
+
+        err
+    }
 }
 
 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {

src/test/ui/mismatched_types/closure-arg-type-mismatch.rs

@@ -0,0 +1,21 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::ops::{FnOnce, Fn};
+
+pub fn main() {
+        let a = [(1u32,2u32)];
+        let b = a.iter().map(|x: (u32, u32)| 45);
+        let d1 = a.iter().map(|x: &(u16,u16)| 45);
+        let d2 = a.iter().map(|x: (u16,u16)| 45);
+        foo(|y: isize| ());
+}
+
+fn foo<F>(m: F) where F: Fn(usize) {}

src/test/ui/mismatched_types/closure-arg-type-mismatch.stderr

@@ -0,0 +1,36 @@
+error[E0622]: type mismatch in closure arguments
+  --> $DIR/closure-arg-type-mismatch.rs:15:26
+   |
+15 |         let b = a.iter().map(|x: (u32, u32)| 45);
+   |                          ^^^ ------------------ takes a `std::ops::FnMut<((u32, u32),)>`
+   |                          |
+   |                          expected closure that takes a `std::ops::FnMut<(&(u32, u32),)>`
+
+error[E0622]: type mismatch in closure arguments
+  --> $DIR/closure-arg-type-mismatch.rs:16:27
+   |
+16 |         let d1 = a.iter().map(|x: &(u16,u16)| 45);
+   |                           ^^^ ------------------ takes a `for<'r> std::ops::FnMut<(&'r (u16, u16),)>`
+   |                           |
+   |                           expected closure that takes a `std::ops::FnMut<(&(u32, u32),)>`
+
+error[E0622]: type mismatch in closure arguments
+  --> $DIR/closure-arg-type-mismatch.rs:17:27
+   |
+17 |         let d2 = a.iter().map(|x: (u16,u16)| 45);
+   |                           ^^^ ----------------- takes a `std::ops::FnMut<((u16, u16),)>`
+   |                           |
+   |                           expected closure that takes a `std::ops::FnMut<(&(u32, u32),)>`
+
+error[E0622]: type mismatch in closure arguments
+  --> $DIR/closure-arg-type-mismatch.rs:18:9
+   |
+18 |         foo(|y: isize| ());
+   |         ^^^ ------------- takes a `std::ops::Fn<(isize,)>`
+   |         |
+   |         expected closure that takes a `std::ops::Fn<(usize,)>`
+   |
+   = note: required by `foo`
+
+error: aborting due to 4 previous errors
+