show a trailing comma on singleton tuple constructors in witness pats

Author: dianne

compiler/rustc_pattern_analysis/src/rustc/print.rs

@@ -119,6 +119,9 @@ pub(crate) fn write_struct_like<'tcx>(
                 write!(f, "_")?;
             }
         }
+        if matches!(ty.kind(), ty::Tuple(..)) && num_fields == 1 {
+            write!(f, ",")?;
+        }
         write!(f, ")")?;
     }
 

tests/ui/or-patterns/exhaustiveness-non-exhaustive.rs

@@ -7,11 +7,11 @@ fn main() {
         (0 | 1, 2 | 3) => {}
     }
     match ((0u8,),) {
-        //~^ ERROR non-exhaustive patterns: `((4_u8..=u8::MAX))`
+        //~^ ERROR non-exhaustive patterns: `((4_u8..=u8::MAX,),)`
         ((0 | 1,) | (2 | 3,),) => {}
     }
     match (Some(0u8),) {
-        //~^ ERROR non-exhaustive patterns: `(Some(2_u8..=u8::MAX))`
+        //~^ ERROR non-exhaustive patterns: `(Some(2_u8..=u8::MAX),)`
         (None | Some(0 | 1),) => {}
     }
 }

tests/ui/or-patterns/exhaustiveness-non-exhaustive.stderr

@@ -11,30 +11,30 @@ LL ~         (0 | 1, 2 | 3) => {},
 LL +         (2_u8..=u8::MAX, _) => todo!()
    |
 
-error[E0004]: non-exhaustive patterns: `((4_u8..=u8::MAX))` not covered
+error[E0004]: non-exhaustive patterns: `((4_u8..=u8::MAX,),)` not covered
   --> $DIR/exhaustiveness-non-exhaustive.rs:9:11
    |
 LL |     match ((0u8,),) {
-   |           ^^^^^^^^^ pattern `((4_u8..=u8::MAX))` not covered
+   |           ^^^^^^^^^ pattern `((4_u8..=u8::MAX,),)` not covered
    |
    = note: the matched value is of type `((u8,),)`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL ~         ((0 | 1,) | (2 | 3,),) => {},
-LL +         ((4_u8..=u8::MAX)) => todo!()
+LL +         ((4_u8..=u8::MAX,),) => todo!()
    |
 
-error[E0004]: non-exhaustive patterns: `(Some(2_u8..=u8::MAX))` not covered
+error[E0004]: non-exhaustive patterns: `(Some(2_u8..=u8::MAX),)` not covered
   --> $DIR/exhaustiveness-non-exhaustive.rs:13:11
    |
 LL |     match (Some(0u8),) {
-   |           ^^^^^^^^^^^^ pattern `(Some(2_u8..=u8::MAX))` not covered
+   |           ^^^^^^^^^^^^ pattern `(Some(2_u8..=u8::MAX),)` not covered
    |
    = note: the matched value is of type `(Option<u8>,)`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL ~         (None | Some(0 | 1),) => {},
-LL +         (Some(2_u8..=u8::MAX)) => todo!()
+LL +         (Some(2_u8..=u8::MAX),) => todo!()
    |
 
 error: aborting due to 3 previous errors