Auto merge of #43251 - gaurikholkar:span_reorder, r=nikomatsakis

Reorder span suggestions to appear below main labels

A fix to #41698

r? @nikomatsakis

Author: bors

src/librustc_errors/emitter.rs

@@ -346,9 +346,20 @@ impl EmitterWriter {
         // and "annotations lines", where the highlight lines have the `^`.
 
         // Sort the annotations by (start, end col)
+        // The labels are reversed, sort and then reversed again.
+        // Consider a list of annotations (A1, A2, C1, C2, B1, B2) where
+        // the letter signifies the span. Here we are only sorting by the
+        // span and hence, the order of the elements with the same span will
+        // not change. On reversing the ordering (|a, b| but b.cmp(a)), you get
+        // (C1, C2, B1, B2, A1, A2). All the elements with the same span are
+        // still ordered first to last, but all the elements with different
+        // spans are ordered by their spans in last to first order. Last to
+        // first order is important, because the jiggly lines and | are on
+        // the left, so the rightmost span needs to be rendered first,
+        // otherwise the lines would end up needing to go over a message.
+
         let mut annotations = line.annotations.clone();
-        annotations.sort();
-        annotations.reverse();
+        annotations.sort_by(|a,b| b.start_col.cmp(&a.start_col));
 
         // First, figure out where each label will be positioned.
         //

src/test/ui/did_you_mean/issue-31424.stderr

@@ -4,8 +4,8 @@ error[E0596]: cannot borrow immutable argument `self` as mutable
 17 |         (&mut self).bar();
    |               ^^^^
    |               |
-   |               try removing `&mut` here
    |               cannot reborrow mutably
+   |               try removing `&mut` here
 
 error[E0596]: cannot borrow immutable argument `self` as mutable
   --> $DIR/issue-31424.rs:23:15

src/test/ui/did_you_mean/issue-34126.stderr

@@ -4,8 +4,8 @@ error[E0596]: cannot borrow immutable argument `self` as mutable
 16 |         self.run(&mut self);
    |                       ^^^^
    |                       |
-   |                       try removing `&mut` here
    |                       cannot reborrow mutably
+   |                       try removing `&mut` here
 
 error: aborting due to previous error
 

src/test/ui/did_you_mean/issue-34337.stderr

@@ -4,8 +4,8 @@ error[E0596]: cannot borrow immutable local variable `key` as mutable
 16 |     get(&mut key);
    |              ^^^
    |              |
-   |              try removing `&mut` here
    |              cannot reborrow mutably
+   |              try removing `&mut` here
 
 error: aborting due to previous error
 

src/test/ui/did_you_mean/issue-37139.stderr

@@ -4,8 +4,8 @@ error[E0596]: cannot borrow immutable local variable `x` as mutable
 22 |             test(&mut x);
    |                       ^
    |                       |
-   |                       try removing `&mut` here
    |                       cannot reborrow mutably
+   |                       try removing `&mut` here
 
 error: aborting due to previous error
 

src/test/ui/issue-40402-ref-hints/issue-40402-1.stderr

@@ -4,8 +4,8 @@ error[E0507]: cannot move out of indexed content
 19 |     let e = f.v[0];
    |             ^^^^^^
    |             |
-   |             help: consider using a reference instead: `&f.v[0]`
    |             cannot move out of indexed content
+   |             help: consider using a reference instead: `&f.v[0]`
 
 error: aborting due to previous error
 

src/test/ui/mismatched_types/E0281.stderr

@@ -4,8 +4,8 @@ error[E0281]: type mismatch: `[closure@$DIR/E0281.rs:14:9: 14:24]` implements th
 14 |     foo(|y: String| { });
    |     ^^^ --------------- implements `std::ops::Fn<(std::string::String,)>`
    |     |
-   |     requires `std::ops::Fn<(usize,)>`
    |     expected usize, found struct `std::string::String`
+   |     requires `std::ops::Fn<(usize,)>`
    |
    = note: required by `foo`
 

src/test/ui/mismatched_types/closure-mismatch.stderr

@@ -14,8 +14,8 @@ error[E0281]: type mismatch: `[closure@$DIR/closure-mismatch.rs:18:9: 18:15]` im
 18 |     baz(|_| ());
    |     ^^^ ------ implements `std::ops::Fn<(_,)>`
    |     |
-   |     requires `for<'r> std::ops::Fn<(&'r (),)>`
    |     expected concrete lifetime, found bound lifetime parameter
+   |     requires `for<'r> std::ops::Fn<(&'r (),)>`
    |
    = note: required because of the requirements on the impl of `Foo` for `[closure@$DIR/closure-mismatch.rs:18:9: 18:15]`
    = note: required by `baz`

src/test/ui/mismatched_types/issue-36053-2.stderr

@@ -14,8 +14,8 @@ error[E0281]: type mismatch: `[closure@$DIR/issue-36053-2.rs:17:39: 17:53]` impl
 17 |     once::<&str>("str").fuse().filter(|a: &str| true).count();
    |                                ^^^^^^ -------------- implements `for<'r> std::ops::FnMut<(&'r str,)>`
    |                                |
-   |                                requires `for<'r> std::ops::FnMut<(&'r &str,)>`
    |                                expected &str, found str
+   |                                requires `for<'r> std::ops::FnMut<(&'r &str,)>`
 
 error: aborting due to 2 previous errors
 

src/test/ui/mismatched_types/unboxed-closures-vtable-mismatch.stderr

@@ -7,8 +7,8 @@ error[E0281]: type mismatch: `[closure@$DIR/unboxed-closures-vtable-mismatch.rs:
 25 |     let z = call_it(3, f);
    |             ^^^^^^^
    |             |
-   |             requires `std::ops::FnMut<(isize, isize)>`
    |             expected isize, found usize
+   |             requires `std::ops::FnMut<(isize, isize)>`
    |
    = note: required by `call_it`