Warning about unreachable arms after matching on a diverging type

3 files changed, 24 insertions, 6 deletions

diff --git a/src/librustc_typeck/check/_match.rs b/src/librustc_typeck/check/_match.rs
index b4c969447de..eaaf9f77430 100644
--- a/src/librustc_typeck/check/_match.rs
+++ b/src/librustc_typeck/check/_match.rs
@@ -614,6 +614,12 @@ https://doc.rust-lang.org/reference/types.html#trait-objects");
             return tcx.types.never;
         }
 
+        if self.diverges.get().always() {
+            for arm in arms {
+                self.warn_if_unreachable(arm.body.id, arm.body.span, "arm");
+            }
+        }
+
         // Otherwise, we have to union together the types that the
         // arms produce and so forth.
         let discrim_diverges = self.diverges.get();
diff --git a/src/test/ui/unreachable/unwarned-match-on-never.rs b/src/test/ui/unreachable/unwarned-match-on-never.rs
index 0c160615c8b..71f8fe3a783 100644
--- a/src/test/ui/unreachable/unwarned-match-on-never.rs
+++ b/src/test/ui/unreachable/unwarned-match-on-never.rs
@@ -7,12 +7,18 @@ fn foo(x: !) -> bool {
     // Explicit matches on the never type are unwarned.
     match x {}
     // But matches in unreachable code are warned.
-    match x {} //~ ERROR: unreachable expression
+    match x {} //~ ERROR unreachable expression
+}
+
+fn bar() {
+    match (return) {
+        () => () //~ ERROR unreachable arm
+    }
 }
 
 fn main() {
     return;
-    match () { //~ ERROR: unreachable expression
+    match () { //~ ERROR unreachable expression
         () => (),
     }
 }
diff --git a/src/test/ui/unreachable/unwarned-match-on-never.stderr b/src/test/ui/unreachable/unwarned-match-on-never.stderr
index 969c24a07e8..8807e5f04e5 100644
--- a/src/test/ui/unreachable/unwarned-match-on-never.stderr
+++ b/src/test/ui/unreachable/unwarned-match-on-never.stderr
@@ -1,7 +1,7 @@
 error: unreachable expression
   --> $DIR/unwarned-match-on-never.rs:10:5
    |
-LL |     match x {} //~ ERROR: unreachable expression
+LL |     match x {} //~ ERROR unreachable expression
    |     ^^^^^^^^^^
    |
 note: lint level defined here
@@ -10,13 +10,19 @@ note: lint level defined here
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
 
+error: unreachable arm
+  --> $DIR/unwarned-match-on-never.rs:15:15
+   |
+LL |         () => () //~ ERROR unreachable arm
+   |               ^^
+
 error: unreachable expression
-  --> $DIR/unwarned-match-on-never.rs:15:5
+  --> $DIR/unwarned-match-on-never.rs:21:5
    |
-LL | /     match () { //~ ERROR: unreachable expression
+LL | /     match () { //~ ERROR unreachable expression
 LL | |         () => (),
 LL | |     }
    | |_____^
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors