Emit lints in the order in which they occur in the file.

Author: Nadrieril

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -390,10 +390,11 @@ fn check_arms<'p, 'tcx>(
                 }
             }
             Useful(unreachables) => {
-                for set in unreachables {
-                    for span in set {
-                        unreachable_pattern(cx.tcx, span, id, None);
-                    }
+                let mut unreachables: Vec<_> = unreachables.into_iter().flatten().collect();
+                // Emit lints in the order in which they occur in the file.
+                unreachables.sort_unstable();
+                for span in unreachables {
+                    unreachable_pattern(cx.tcx, span, id, None);
                 }
             }
             UsefulWithWitness(_) => bug!(),

src/test/ui/or-patterns/exhaustiveness-unreachable-pattern.stderr

@@ -77,15 +77,15 @@ LL |         (1 | 1,) => {}
    |              ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:55:15
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:53:15
    |
-LL |             | 0] => {}
+LL |             | 0
    |               ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:53:15
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:55:15
    |
-LL |             | 0
+LL |             | 0] => {}
    |               ^
 
 error: unreachable pattern