Rollup merge of rust-lang#47407 - gaurikholkar:master, r=estebank

fix mispositioned span

This fixes rust-lang#47377

The output now looks like this
```
error[E0369]: binary operation `+` cannot be applied to type `&str`
 --> h.rs:3:11
  |
3 |     let _a = b + ", World!";
  |              ^^^^^^^^^^^^^^ `+` can't be used to concatenate two `&str` strings
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
  |
3 |     let _a = b.to_owned() + ", World!";
  |              ^^^^^^^^^

error: aborting due to previous error
```
For the case when emojis are involved,  it gives the new output for proper indentation.
But for an indentation as follows,
```
fn main() {
let b = "hello";
    let _a = b + ", World!";
}
```
it still mispositions the span
```
3 |     println!("🦀🦀🦀🦀🦀"); let _a = b + ", World!";
  |                                           ^^^^^^^^^^^^^^ `+` can't be used to concatenate two `&str` strings
  |
3 |     println!("🦀🦀🦀🦀🦀"); let _a = b.to_owned() + ", World!";
  |                                           ^^^^^^^
error: aborting due to previous erro
```

cc @estebank  @est31

src/librustc_errors/emitter.rs

@@ -1187,8 +1187,8 @@ impl EmitterWriter {
                     let sub_len = parts[0].snippet.trim().chars().fold(0, |acc, ch| {
                         acc + unicode_width::UnicodeWidthChar::width(ch).unwrap_or(0)
                     });
-                    let underline_start = span_start_pos.col.0 + start;
-                    let underline_end = span_start_pos.col.0 + start + sub_len;
+                    let underline_start = span_start_pos.col_display + start;
+                    let underline_end = span_start_pos.col_display + start + sub_len;
                     for p in underline_start..underline_end {
                         buffer.putc(row_num,
                                     max_line_num_len + 3 + p,

src/test/ui/issue-47377.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.
+// ignore-tidy-tab
+fn main() {
+ 	let b = "hello";
+ 	let _a = b + ", World!";
+ 	//~^ ERROR E0369
+}

src/test/ui/issue-47377.stderr

@@ -0,0 +1,12 @@
+error[E0369]: binary operation `+` cannot be applied to type `&str`
+  --> $DIR/issue-47377.rs:13:12
+   |
+13 |      let _a = b + ", World!";
+   |               ^^^^^^^^^^^^^^ `+` can't be used to concatenate two `&str` strings
+help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   |
+13 |      let _a = b.to_owned() + ", World!";
+   |               ^^^^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/issue-47380.rs

@@ -0,0 +1,14 @@
+// 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() {
+    let b = "hello";
+    println!("🦀🦀🦀🦀🦀"); let _a = b + ", World!";
+    //~^ ERROR E0369
+}

src/test/ui/issue-47380.stderr

@@ -0,0 +1,12 @@
+error[E0369]: binary operation `+` cannot be applied to type `&str`
+  --> $DIR/issue-47380.rs:12:33
+   |
+12 |     println!("🦀🦀🦀🦀🦀"); let _a = b + ", World!";
+   |                                      ^^^^^^^^^^^^^^ `+` can't be used to concatenate two `&str` strings
+help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
+   |
+12 |     println!("🦀🦀🦀🦀🦀"); let _a = b.to_owned() + ", World!";
+   |                                      ^^^^^^^^^^^^
+
+error: aborting due to previous error
+