Auto merge of #40565 - estebank:binops-help, r=arielb1

Explicit help message for binop type mismatch

When trying to do `1 + Some(2)`, or some other binary operation on two
types different types without an appropriate trait implementation, provide
an explicit help message:

```rust
help: `{integer} + std::option::Option<{integer}>` has no implementation
```

Re: #39579, #38564, #37626, #39942, #34698.

src/test/ui/impl-trait/equality.rs

@@ -0,0 +1,72 @@
+// 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.
+
+#![feature(conservative_impl_trait, specialization)]
+
+trait Foo: Copy + ToString {}
+
+impl<T: Copy + ToString> Foo for T {}
+
+fn hide<T: Foo>(x: T) -> impl Foo {
+    x
+}
+
+fn two(x: bool) -> impl Foo {
+    if x {
+        return 1_i32;
+    }
+    0_u32
+    //~^ ERROR mismatched types
+    //~| expected i32, found u32
+}
+
+fn sum_to(n: u32) -> impl Foo {
+    if n == 0 {
+        0
+    } else {
+        n + sum_to(n - 1)
+        //~^ ERROR no implementation for `u32 + impl Foo`
+    }
+}
+
+trait Leak: Sized {
+    type T;
+    fn leak(self) -> Self::T;
+}
+impl<T> Leak for T {
+    default type T = ();
+    default fn leak(self) -> Self::T { panic!() }
+}
+impl Leak for i32 {
+    type T = i32;
+    fn leak(self) -> i32 { self }
+}
+
+fn main() {
+    let _: u32 = hide(0_u32);
+    //~^ ERROR mismatched types
+    //~| expected type `u32`
+    //~| found type `impl Foo`
+    //~| expected u32, found anonymized type
+
+    let _: i32 = Leak::leak(hide(0_i32));
+    //~^ ERROR mismatched types
+    //~| expected type `i32`
+    //~| found type `<impl Foo as Leak>::T`
+    //~| expected i32, found associated type
+
+    let mut x = (hide(0_u32), hide(0_i32));
+    x = (x.1,
+    //~^ ERROR mismatched types
+    //~| expected u32, found i32
+         x.0);
+    //~^ ERROR mismatched types
+    //~| expected i32, found u32
+}

src/test/ui/impl-trait/equality.stderr

@@ -0,0 +1,55 @@
+error[E0308]: mismatched types
+  --> $DIR/equality.rs:25:5
+   |
+25 |     0_u32
+   |     ^^^^^ expected i32, found u32
+   |
+   = note: expected type `i32`
+              found type `u32`
+
+error[E0277]: the trait bound `u32: std::ops::Add<impl Foo>` is not satisfied
+  --> $DIR/equality.rs:34:9
+   |
+34 |         n + sum_to(n - 1)
+   |         ^^^^^^^^^^^^^^^^^ the trait `std::ops::Add<impl Foo>` is not implemented for `u32`
+   |
+   = note: no implementation for `u32 + impl Foo`
+
+error[E0308]: mismatched types
+  --> $DIR/equality.rs:53:18
+   |
+53 |     let _: u32 = hide(0_u32);
+   |                  ^^^^^^^^^^^ expected u32, found anonymized type
+   |
+   = note: expected type `u32`
+              found type `impl Foo`
+
+error[E0308]: mismatched types
+  --> $DIR/equality.rs:59:18
+   |
+59 |     let _: i32 = Leak::leak(hide(0_i32));
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^ expected i32, found associated type
+   |
+   = note: expected type `i32`
+              found type `<impl Foo as Leak>::T`
+
+error[E0308]: mismatched types
+  --> $DIR/equality.rs:66:10
+   |
+66 |     x = (x.1,
+   |          ^^^ expected u32, found i32
+   |
+   = note: expected type `impl Foo` (u32)
+              found type `impl Foo` (i32)
+
+error[E0308]: mismatched types
+  --> $DIR/equality.rs:69:10
+   |
+69 |          x.0);
+   |          ^^^ expected i32, found u32
+   |
+   = note: expected type `impl Foo` (i32)
+              found type `impl Foo` (u32)
+
+error: aborting due to 6 previous errors
+

src/test/ui/mismatched_types/binops.rs

@@ -0,0 +1,18 @@
+// 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 + Some(1);
+    2 as usize - Some(1);
+    3 * ();
+    4 / "";
+    5 < String::new();
+    6 == Ok(1);
+}

src/test/ui/mismatched_types/binops.stderr

@@ -0,0 +1,58 @@
+error[E0277]: the trait bound `{integer}: std::ops::Add<std::option::Option<{integer}>>` is not satisfied
+  --> $DIR/binops.rs:12:5
+   |
+12 |     1 + Some(1);
+   |     ^^^^^^^^^^^ the trait `std::ops::Add<std::option::Option<{integer}>>` is not implemented for `{integer}`
+   |
+   = note: no implementation for `{integer} + std::option::Option<{integer}>`
+
+error[E0277]: the trait bound `usize: std::ops::Sub<std::option::Option<{integer}>>` is not satisfied
+  --> $DIR/binops.rs:13:5
+   |
+13 |     2 as usize - Some(1);
+   |     ^^^^^^^^^^^^^^^^^^^^ the trait `std::ops::Sub<std::option::Option<{integer}>>` is not implemented for `usize`
+   |
+   = note: no implementation for `usize - std::option::Option<{integer}>`
+
+error[E0277]: the trait bound `{integer}: std::ops::Mul<()>` is not satisfied
+  --> $DIR/binops.rs:14:5
+   |
+14 |     3 * ();
+   |     ^^^^^^ the trait `std::ops::Mul<()>` is not implemented for `{integer}`
+   |
+   = note: no implementation for `{integer} * ()`
+
+error[E0277]: the trait bound `{integer}: std::ops::Div<&str>` is not satisfied
+  --> $DIR/binops.rs:15:5
+   |
+15 |     4 / "";
+   |     ^^^^^^ the trait `std::ops::Div<&str>` is not implemented for `{integer}`
+   |
+   = note: no implementation for `{integer} / &str`
+
+error[E0277]: the trait bound `{integer}: std::cmp::PartialEq<std::string::String>` is not satisfied
+  --> $DIR/binops.rs:16:5
+   |
+16 |     5 < String::new();
+   |     ^^^^^^^^^^^^^^^^^ the trait `std::cmp::PartialEq<std::string::String>` is not implemented for `{integer}`
+   |
+   = note: can't compare `{integer}` with `std::string::String`
+
+error[E0277]: the trait bound `{integer}: std::cmp::PartialOrd<std::string::String>` is not satisfied
+  --> $DIR/binops.rs:16:5
+   |
+16 |     5 < String::new();
+   |     ^^^^^^^^^^^^^^^^^ the trait `std::cmp::PartialOrd<std::string::String>` is not implemented for `{integer}`
+   |
+   = note: can't compare `{integer}` with `std::string::String`
+
+error[E0277]: the trait bound `{integer}: std::cmp::PartialEq<std::result::Result<{integer}, _>>` is not satisfied
+  --> $DIR/binops.rs:17:5
+   |
+17 |     6 == Ok(1);
+   |     ^^^^^^^^^^ the trait `std::cmp::PartialEq<std::result::Result<{integer}, _>>` is not implemented for `{integer}`
+   |
+   = note: can't compare `{integer}` with `std::result::Result<{integer}, _>`
+
+error: aborting due to 7 previous errors
+

src/test/ui/span/multiline-span-simple.stderr

@@ -9,11 +9,7 @@ error[E0277]: the trait bound `u32: std::ops::Add<()>` is not satisfied
 27 | |             y),
    | |______________^ ...ending here: the trait `std::ops::Add<()>` is not implemented for `u32`
    |
-   = help: the following implementations were found:
-             <u32 as std::ops::Add>
-             <&'a u32 as std::ops::Add<u32>>
-             <u32 as std::ops::Add<&'a u32>>
-             <&'b u32 as std::ops::Add<&'a u32>>
+   = note: no implementation for `u32 + ()`
 
 error: aborting due to previous error