Prioritize Primary underline for overlapping spans of same length

Author: estebank

src/librustc_errors/emitter.rs

@@ -678,8 +678,8 @@ impl EmitterWriter {
         //   | |  something about `foo`
         //   | something about `fn foo()`
         annotations_position.sort_by(|a, b| {
-            // Decreasing order
-            a.1.len().cmp(&b.1.len()).reverse()
+            // Decreasing order. When `a` and `b` are the same length, prefer `Primary`.
+            (a.1.len(), !a.1.is_primary).cmp(&(b.1.len(), !b.1.is_primary)).reverse()
         });
 
         // Write the underlines.

src/test/ui/augmented-assignments.nll.stderr

@@ -9,7 +9,7 @@ LL |       x   //~ error: use of moved value: `x`
 LL | |     //~^ value used here after move
 LL | |     +=
 LL | |     x;  //~ value moved here
-   | |     -
+   | |     ^
    | |     |
    | |_____move out of `x` occurs here
    |       borrow later used here

src/test/ui/resolve/token-error-correct-3.stderr

@@ -13,7 +13,7 @@ error: expected one of `)`, `,`, `.`, `?`, or an operator, found `;`
   --> $DIR/token-error-correct-3.rs:24:35
    |
 LL |             callback(path.as_ref();
-   |                     -             -
+   |                     -             ^
    |                     |             |
    |                     |             expected one of `)`, `,`, `.`, `?`, or an operator here
    |                     |             help: ...the missing `)` may belong here

src/test/ui/resolve/token-error-correct.stderr

@@ -13,7 +13,7 @@ error: expected expression, found `;`
   --> $DIR/token-error-correct.rs:14:13
    |
 LL |     foo(bar(;
-   |        -    -
+   |        -    ^
    |        |    |
    |        |    expected expression
    |        |    help: ...the missing `)` may belong here
@@ -23,7 +23,7 @@ error: expected one of `)`, `,`, `-`, `.`, `<`, `?`, `break`, `continue`, `false
   --> $DIR/token-error-correct.rs:14:13
    |
 LL |     foo(bar(;
-   |            --
+   |            -^
    |            ||
    |            |expected one of 21 possible tokens here
    |            |help: ...the missing `)` may belong here

src/test/ui/token/issue-10636-2.stderr

@@ -13,7 +13,7 @@ error: expected one of `)`, `,`, `.`, `?`, or an operator, found `;`
   --> $DIR/issue-10636-2.rs:15:25
    |
 LL |     option.map(|some| 42;
-   |               -         -
+   |               -         ^
    |               |         |
    |               |         expected one of `)`, `,`, `.`, `?`, or an operator here
    |               |         help: ...the missing `)` may belong here