Auto merge of #41488 - estebank:closure-args, r=arielb1

Clean up callable type mismatch errors

```rust
error[E0593]: closure takes 1 argument but 2 arguments are required here
  --> ../../src/test/ui/mismatched_types/closure-arg-count.rs:13:15
   |
13 |     [1, 2, 3].sort_by(|(tuple, tuple2)| panic!());
   |               ^^^^^^^ -------------------------- takes 1 argument
   |               |
   |               expected closure that takes 2 arguments
```

instead of

```rust
error[E0281]: type mismatch: the type `[closure@../../src/test/ui/mismatched_types/closure-arg-count.rs:13:23: 13:49]` implements the trait `for<'r> std::ops::FnMut<(&'r {integer},)>`, but the trait `for<'r, 'r> std::ops::FnMut<(&'r {integer}, &'r {integer})>` is required (expected a tuple with 2 elements, found one with 1 elements)
  --> ../../src/test/ui/mismatched_types/closure-arg-count.rs:13:15
   |
13 |     [1, 2, 3].sort_by(|(tuple, tuple2)| panic!());
   |               ^^^^^^^
```

Fix #21857, re #24680.

src/librustc/diagnostics.rs

@@ -1049,18 +1049,19 @@ which expected that trait. This error typically occurs when working with
 `Fn`-based types. Erroneous code example:
 
 ```compile_fail,E0281
-fn foo<F: Fn()>(x: F) { }
+fn foo<F: Fn(usize)>(x: F) { }
 
 fn main() {
-    // type mismatch: the type ... implements the trait `core::ops::Fn<(_,)>`,
-    // but the trait `core::ops::Fn<()>` is required (expected (), found tuple
+    // type mismatch: ... implements the trait `core::ops::Fn<(String,)>`,
+    // but the trait `core::ops::Fn<(usize,)>` is required
     // [E0281]
-    foo(|y| { });
+    foo(|y: String| { });
 }
 ```
 
-The issue in this case is that `foo` is defined as accepting a `Fn` with no
-arguments, but the closure we attempted to pass to it requires one argument.
+The issue in this case is that `foo` is defined as accepting a `Fn` with one
+argument of type `String`, but the closure we attempted to pass to it requires
+one arguments of type `usize`.
 "##,
 
 E0282: r##"
@@ -1807,6 +1808,20 @@ makes a difference in practice.)
 [rfc401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md
 "##,
 
+E0593: r##"
+You tried to supply an `Fn`-based type with an incorrect number of arguments
+than what was expected. Erroneous code example:
+
+```compile_fail,E0593
+fn foo<F: Fn()>(x: F) { }
+
+fn main() {
+    // [E0593] closure takes 1 argument but 0 arguments are required
+    foo(|y| { });
+}
+```
+"##,
+
 }
 
 

src/librustc/traits/error_reporting.rs

@@ -35,7 +35,7 @@ use rustc::lint::builtin::EXTRA_REQUIREMENT_IN_IMPL;
 use std::fmt;
 use syntax::ast::{self, NodeId};
 use ty::{self, AdtKind, ToPredicate, ToPolyTraitRef, Ty, TyCtxt, TypeFoldable, TyInfer, TyVar};
-use ty::error::ExpectedFound;
+use ty::error::{ExpectedFound, TypeError};
 use ty::fast_reject;
 use ty::fold::TypeFolder;
 use ty::subst::Subst;
@@ -663,13 +663,54 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 if actual_trait_ref.self_ty().references_error() {
                     return;
                 }
-                struct_span_err!(self.tcx.sess, span, E0281,
-                    "type mismatch: the type `{}` implements the trait `{}`, \
-                     but the trait `{}` is required ({})",
-                    expected_trait_ref.self_ty(),
-                    expected_trait_ref,
-                    actual_trait_ref,
-                    e)
+                let expected_trait_ty = expected_trait_ref.self_ty();
+                let found_span = expected_trait_ty.ty_to_def_id().and_then(|did| {
+                    self.tcx.hir.span_if_local(did)
+                });
+
+                if let &TypeError::TupleSize(ref expected_found) = e {
+                    // Expected `|x| { }`, found `|x, y| { }`
+                    self.report_arg_count_mismatch(span,
+                                                   found_span,
+                                                   expected_found.expected,
+                                                   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())
+                    } else {
+                        self.report_type_argument_mismatch(span,
+                                                            found_span,
+                                                            expected_trait_ty,
+                                                            expected_trait_ref,
+                                                            actual_trait_ref,
+                                                            e)
+                    }
+                } else {
+                    self.report_type_argument_mismatch(span,
+                                                        found_span,
+                                                        expected_trait_ty,
+                                                        expected_trait_ref,
+                                                        actual_trait_ref,
+                                                        e)
+                }
             }
 
             TraitNotObjectSafe(did) => {
@@ -681,6 +722,60 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         self.note_obligation_cause(&mut err, obligation);
         err.emit();
     }
+
+    fn report_type_argument_mismatch(&self,
+                                      span: Span,
+                                      found_span: Option<Span>,
+                                      expected_ty: Ty<'tcx>,
+                                      expected_ref: ty::PolyTraitRef<'tcx>,
+                                      found_ref: ty::PolyTraitRef<'tcx>,
+                                      type_error: &TypeError<'tcx>)
+        -> DiagnosticBuilder<'tcx>
+    {
+        let mut err = struct_span_err!(self.tcx.sess, span, E0281,
+            "type mismatch: `{}` implements the trait `{}`, but the trait `{}` is required",
+            expected_ty,
+            expected_ref,
+            found_ref);
+
+        err.span_label(span, &format!("{}", type_error));
+
+        if let Some(sp) = found_span {
+            err.span_label(span, &format!("requires `{}`", found_ref));
+            err.span_label(sp, &format!("implements `{}`", expected_ref));
+        }
+
+        err
+    }
+
+    fn report_arg_count_mismatch(&self,
+                                 span: Span,
+                                 found_span: Option<Span>,
+                                 expected: usize,
+                                 found: usize,
+                                 is_closure: bool)
+        -> DiagnosticBuilder<'tcx>
+    {
+        let mut err = struct_span_err!(self.tcx.sess, span, E0593,
+            "{} takes {} argument{} but {} argument{} {} required",
+            if is_closure { "closure" } else { "function" },
+            found,
+            if found == 1 { "" } else { "s" },
+            expected,
+            if expected == 1 { "" } else { "s" },
+            if expected == 1 { "is" } else { "are" });
+
+        err.span_label(span, &format!("expected {} that takes {} argument{}",
+                                      if is_closure { "closure" } else { "function" },
+                                      expected,
+                                      if expected == 1 { "" } else { "s" }));
+        if let Some(span) = found_span {
+            err.span_label(span, &format!("takes {} argument{}",
+                                          found,
+                                          if found == 1 { "" } else { "s" }));
+        }
+        err
+    }
 }
 
 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {

src/librustc/ty/error.rs

@@ -117,12 +117,16 @@ impl<'tcx> fmt::Display for TypeError<'tcx> {
                 write!(f, "lifetimes do not intersect")
             }
             RegionsInsufficientlyPolymorphic(br, _, _) => {
-                write!(f, "expected bound lifetime parameter {}, \
-                           found concrete lifetime", br)
+                write!(f,
+                       "expected bound lifetime parameter{}{}, found concrete lifetime",
+                       if br.is_named() { " " } else { "" },
+                       br)
             }
             RegionsOverlyPolymorphic(br, _, _) => {
-                write!(f, "expected concrete lifetime, \
-                           found bound lifetime parameter {}", br)
+                write!(f,
+                       "expected concrete lifetime, found bound lifetime parameter{}{}",
+                       if br.is_named() { " " } else { "" },
+                       br)
             }
             Sorts(values) => ty::tls::with(|tcx| {
                 report_maybe_different(f, values.expected.sort_string(tcx),

src/librustc/ty/sty.rs

@@ -68,6 +68,15 @@ pub enum BoundRegion {
     BrEnv,
 }
 
+impl BoundRegion {
+    pub fn is_named(&self) -> bool {
+        match *self {
+            BoundRegion::BrNamed(..) => true,
+            _ => false,
+        }
+    }
+}
+
 /// When a region changed from late-bound to early-bound when #32330
 /// was fixed, its `RegionParameterDef` will have one of these
 /// structures that we can use to give nicer errors.
@@ -1193,6 +1202,13 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
         }
     }
 
+    pub fn is_closure(&self) -> bool {
+        match self.sty {
+            TyClosure(..) => true,
+            _ => false,
+        }
+    }
+
     pub fn is_integral(&self) -> bool {
         match self.sty {
             TyInfer(IntVar(_)) | TyInt(_) | TyUint(_) => true,

src/test/ui/mismatched_types/E0281.rs

@@ -0,0 +1,25 @@
+// Copyright 2016 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.
+
+fn foo<F: Fn(usize)>(x: F) { }
+
+fn main() {
+    foo(|y: String| { });
+    //~^ ERROR E0281
+    //~| ERROR E0281
+    //~| NOTE implements
+    //~| NOTE implements
+    //~| NOTE requires
+    //~| NOTE requires
+    //~| NOTE expected usize, found struct `std::string::String`
+    //~| NOTE expected usize, found struct `std::string::String`
+    //~| NOTE required by `foo`
+    //~| NOTE required by `foo`
+}

src/test/ui/mismatched_types/E0281.stderr

@@ -0,0 +1,24 @@
+error[E0281]: type mismatch: `[closure@$DIR/E0281.rs:14:9: 14:24]` implements the trait `std::ops::Fn<(std::string::String,)>`, but the trait `std::ops::Fn<(usize,)>` is required
+  --> $DIR/E0281.rs:14:5
+   |
+14 |     foo(|y: String| { });
+   |     ^^^ --------------- implements `std::ops::Fn<(std::string::String,)>`
+   |     |
+   |     requires `std::ops::Fn<(usize,)>`
+   |     expected usize, found struct `std::string::String`
+   |
+   = note: required by `foo`
+
+error[E0281]: type mismatch: `[closure@$DIR/E0281.rs:14:9: 14:24]` implements the trait `std::ops::FnOnce<(std::string::String,)>`, but the trait `std::ops::FnOnce<(usize,)>` is required
+  --> $DIR/E0281.rs:14:5
+   |
+14 |     foo(|y: String| { });
+   |     ^^^ --------------- implements `std::ops::FnOnce<(std::string::String,)>`
+   |     |
+   |     requires `std::ops::FnOnce<(usize,)>`
+   |     expected usize, found struct `std::string::String`
+   |
+   = note: required by `foo`
+
+error: aborting due to 2 previous errors
+

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

@@ -0,0 +1,15 @@
+// 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.
+
+fn main() {
+    [1, 2, 3].sort_by(|| panic!());
+    [1, 2, 3].sort_by(|tuple| panic!());
+    [1, 2, 3].sort_by(|(tuple, tuple2)| panic!());
+}

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

@@ -0,0 +1,59 @@
+error[E0593]: closure takes 0 arguments but 2 arguments are required
+  --> $DIR/closure-arg-count.rs:12:15
+   |
+12 |     [1, 2, 3].sort_by(|| panic!());
+   |               ^^^^^^^ ----------- takes 0 arguments
+   |               |
+   |               expected closure that takes 2 arguments
+
+error[E0593]: closure takes 0 arguments but 2 arguments are required
+  --> $DIR/closure-arg-count.rs:12:15
+   |
+12 |     [1, 2, 3].sort_by(|| panic!());
+   |               ^^^^^^^ ----------- takes 0 arguments
+   |               |
+   |               expected closure that takes 2 arguments
+
+error[E0593]: closure takes 1 argument but 2 arguments are required
+  --> $DIR/closure-arg-count.rs:13:15
+   |
+13 |     [1, 2, 3].sort_by(|tuple| panic!());
+   |               ^^^^^^^ ---------------- takes 1 argument
+   |               |
+   |               expected closure that takes 2 arguments
+
+error[E0593]: closure takes 1 argument but 2 arguments are required
+  --> $DIR/closure-arg-count.rs:13:15
+   |
+13 |     [1, 2, 3].sort_by(|tuple| panic!());
+   |               ^^^^^^^ ---------------- takes 1 argument
+   |               |
+   |               expected closure that takes 2 arguments
+
+error[E0308]: mismatched types
+  --> $DIR/closure-arg-count.rs:14:24
+   |
+14 |     [1, 2, 3].sort_by(|(tuple, tuple2)| panic!());
+   |                        ^^^^^^^^^^^^^^^ expected &{integer}, found tuple
+   |
+   = note: expected type `&{integer}`
+              found type `(_, _)`
+
+error[E0593]: closure takes 1 argument but 2 arguments are required
+  --> $DIR/closure-arg-count.rs:14:15
+   |
+14 |     [1, 2, 3].sort_by(|(tuple, tuple2)| panic!());
+   |               ^^^^^^^ -------------------------- takes 1 argument
+   |               |
+   |               expected closure that takes 2 arguments
+
+error[E0593]: closure takes 1 argument but 2 arguments are required
+  --> $DIR/closure-arg-count.rs:14:15
+   |
+14 |     [1, 2, 3].sort_by(|(tuple, tuple2)| panic!());
+   |               ^^^^^^^ -------------------------- takes 1 argument
+   |               |
+   |               expected closure that takes 2 arguments
+
+error: aborting due to 7 previous errors
+

src/test/compile-fail/E0281.rs → src/test/ui/mismatched_types/closure-mismatch.rs

@@ -1,4 +1,4 @@
-// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// 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.
 //
@@ -8,9 +8,12 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-fn foo<F: Fn()>(x: F) { }
+trait Foo {}
+
+impl<T: Fn(&())> Foo for T {}
+
+fn baz<T: Foo>(_: T) {}
 
 fn main() {
-    foo(|y| { }); //~ ERROR E0281
-                  //~^ ERROR E0281
+    baz(|_| ());
 }