Auto merge of #47690 - estebank:for-block-277, r=nikomatsakis

For E0277 on `for` loops, point at the "head" expression

When E0277's span points at a `for` loop, the actual issue is in the
element being iterated. Instead of pointing at the entire loop, point
only at the first line (when possible) so that the span ends in the
element for which E0277 was triggered.

src/test/ui/const-fn-error.stderr

@@ -13,22 +13,16 @@ error[E0016]: blocks in constant functions are limited to items and tail express
    |                   ^
 
 error[E0015]: calls in constant functions are limited to constant functions, struct and enum constructors
-  --> $DIR/const-fn-error.rs:17:5
+  --> $DIR/const-fn-error.rs:17:14
    |
-17 | /     for i in 0..x { //~ ERROR calls in constant functions
-18 | |     //~| ERROR constant function contains unimplemented
-19 | |         sum += i;
-20 | |     }
-   | |_____^
+17 |     for i in 0..x { //~ ERROR calls in constant functions
+   |              ^^^^
 
 error[E0019]: constant function contains unimplemented expression type
-  --> $DIR/const-fn-error.rs:17:5
+  --> $DIR/const-fn-error.rs:17:14
    |
-17 | /     for i in 0..x { //~ ERROR calls in constant functions
-18 | |     //~| ERROR constant function contains unimplemented
-19 | |         sum += i;
-20 | |     }
-   | |_____^
+17 |     for i in 0..x { //~ ERROR calls in constant functions
+   |              ^^^^
 
 error[E0080]: constant evaluation error
   --> $DIR/const-fn-error.rs:21:5

src/test/ui/issue-33941.stderr

@@ -8,10 +8,10 @@ error[E0271]: type mismatch resolving `<std::collections::hash_map::Iter<'_, _,
               found type `&_`
 
 error[E0271]: type mismatch resolving `<std::collections::hash_map::Iter<'_, _, _> as std::iter::Iterator>::Item == &_`
-  --> $DIR/issue-33941.rs:14:5
+  --> $DIR/issue-33941.rs:14:14
    |
 14 |     for _ in HashMap::new().iter().cloned() {} //~ ERROR type mismatch
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected tuple, found reference
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected tuple, found reference
    |
    = note: expected type `(&_, &_)`
               found type `&_`

src/test/ui/suggestions/for-c-in-str.rs

@@ -0,0 +1,21 @@
+// Copyright 2018 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.
+
+// E0277 should point exclusively at line 14, not the entire for loop span
+
+fn main() {
+    for c in "asdf" {
+    //~^ ERROR the trait bound `&str: std::iter::Iterator` is not satisfied
+    //~| NOTE `&str` is not an iterator
+    //~| HELP the trait `std::iter::Iterator` is not implemented for `&str`
+    //~| NOTE required by `std::iter::IntoIterator::into_iter`
+        println!("");
+    }
+}

src/test/ui/suggestions/for-c-in-str.stderr

@@ -0,0 +1,11 @@
+error[E0277]: the trait bound `&str: std::iter::Iterator` is not satisfied
+  --> $DIR/for-c-in-str.rs:14:14
+   |
+14 |     for c in "asdf" {
+   |              ^^^^^^ `&str` is not an iterator; maybe try calling `.iter()` or a similar method
+   |
+   = help: the trait `std::iter::Iterator` is not implemented for `&str`
+   = note: required by `std::iter::IntoIterator::into_iter`
+
+error: aborting due to previous error
+

src/test/ui/suggestions/try-on-option.stderr

@@ -10,10 +10,7 @@ error[E0277]: the `?` operator can only be used in a function that returns `Resu
   --> $DIR/try-on-option.rs:23:5
    |
 23 |     x?; //~ the `?` operator
-   |     --
-   |     |
-   |     cannot use the `?` operator in a function that returns `u32`
-   |     in this macro invocation
+   |     ^^ cannot use the `?` operator in a function that returns `u32`
    |
    = help: the trait `std::ops::Try` is not implemented for `u32`
    = note: required by `std::ops::Try::from_error`

src/test/ui/suggestions/try-operator-on-main.stderr

@@ -2,10 +2,7 @@ error[E0277]: the `?` operator can only be used in a function that returns `Resu
   --> $DIR/try-operator-on-main.rs:19:5
    |
 19 |     std::fs::File::open("foo")?; //~ ERROR the `?` operator can only
-   |     ---------------------------
-   |     |
-   |     cannot use the `?` operator in a function that returns `()`
-   |     in this macro invocation
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `()`
    |
    = help: the trait `std::ops::Try` is not implemented for `()`
    = note: required by `std::ops::Try::from_error`
@@ -14,10 +11,7 @@ error[E0277]: the `?` operator can only be applied to values that implement `std
   --> $DIR/try-operator-on-main.rs:22:5
    |
 22 |     ()?; //~ ERROR the `?` operator can only
-   |     ---
-   |     |
-   |     the `?` operator cannot be applied to type `()`
-   |     in this macro invocation
+   |     ^^^ the `?` operator cannot be applied to type `()`
    |
    = help: the trait `std::ops::Try` is not implemented for `()`
    = note: required by `std::ops::Try::into_result`
@@ -38,10 +32,7 @@ error[E0277]: the `?` operator can only be applied to values that implement `std
   --> $DIR/try-operator-on-main.rs:32:5
    |
 32 |     ()?; //~ ERROR the `?` operator can only
-   |     ---
-   |     |
-   |     the `?` operator cannot be applied to type `()`
-   |     in this macro invocation
+   |     ^^^ the `?` operator cannot be applied to type `()`
    |
    = help: the trait `std::ops::Try` is not implemented for `()`
    = note: required by `std::ops::Try::into_result`