In rustc_pattern_analysis, put true witnesses before false witnesses

In rustc it doesn't really matter what the order of the witnesses is, but I'm planning to use the witnesses for implementing the "add missing match arms" assist in rust-analyzer, and there `true` before `false` is the natural order (like `Some` before `None`), and also what the current assist does.

The current order doesn't seem to be intentional; the code was created when bool ctors became their own thing, not just int ctors, but for integer, 0 before 1 is indeed the natural order.

Author: ChayimFriedman2

compiler/rustc_pattern_analysis/src/constructor.rs

@@ -1130,16 +1130,16 @@ impl<Cx: PatCx> ConstructorSet<Cx> {
                         seen_false = true;
                     }
                 }
-                if seen_false {
-                    present.push(Bool(false));
-                } else {
-                    missing.push(Bool(false));
-                }
                 if seen_true {
                     present.push(Bool(true));
                 } else {
                     missing.push(Bool(true));
                 }
+                if seen_false {
+                    present.push(Bool(false));
+                } else {
+                    missing.push(Bool(false));
+                }
             }
             ConstructorSet::Integers { range_1, range_2 } => {
                 let seen_ranges: Vec<_> =

compiler/rustc_pattern_analysis/tests/exhaustiveness.rs

@@ -176,6 +176,9 @@ fn test_witnesses() {
         ),
         vec!["Enum::Variant1(_)", "Enum::Variant2(_)", "_"],
     );
+
+    // Assert we put `true` before `false`.
+    assert_witnesses(AllOfThem, Ty::Bool, Vec::new(), vec!["true", "false"]);
 }
 
 #[test]

tests/ui/pattern/deref-patterns/usefulness/non-exhaustive.rs

@@ -15,7 +15,7 @@ fn main() {
     }
 
     match Box::new((true, Box::new(false))) {
-        //~^ ERROR non-exhaustive patterns: `deref!((false, deref!(false)))` and `deref!((true, deref!(true)))` not covered
+        //~^ ERROR non-exhaustive patterns: `deref!((true, deref!(true)))` and `deref!((false, deref!(false)))` not covered
         (true, false) => {}
         (false, true) => {}
     }

tests/ui/pattern/deref-patterns/usefulness/non-exhaustive.stderr

@@ -28,19 +28,19 @@ LL ~         true => {},
 LL +         deref!(deref!(false)) => todo!()
    |
 
-error[E0004]: non-exhaustive patterns: `deref!((false, deref!(false)))` and `deref!((true, deref!(true)))` not covered
+error[E0004]: non-exhaustive patterns: `deref!((true, deref!(true)))` and `deref!((false, deref!(false)))` not covered
   --> $DIR/non-exhaustive.rs:17:11
    |
 LL |     match Box::new((true, Box::new(false))) {
-   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ patterns `deref!((false, deref!(false)))` and `deref!((true, deref!(true)))` not covered
+   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ patterns `deref!((true, deref!(true)))` and `deref!((false, deref!(false)))` not covered
    |
 note: `Box<(bool, Box<bool>)>` defined here
   --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
    = note: the matched value is of type `Box<(bool, Box<bool>)>`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern, a match arm with multiple or-patterns as shown, or multiple match arms
    |
 LL ~         (false, true) => {},
-LL +         deref!((false, deref!(false))) | deref!((true, deref!(true))) => todo!()
+LL +         deref!((true, deref!(true))) | deref!((false, deref!(false))) => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `deref!((deref!(T::C), _))` not covered

tests/ui/pattern/usefulness/unions.rs

@@ -26,7 +26,7 @@ fn main() {
         }
         // Our approach can report duplicate witnesses sometimes.
         match (x, true) {
-            //~^ ERROR non-exhaustive patterns: `(U8AsBool { n: 0_u8 }, false)`, `(U8AsBool { b: false }, false)`, `(U8AsBool { n: 0_u8 }, false)` and 1 more not covered
+            //~^ ERROR non-exhaustive patterns: `(U8AsBool { n: 0_u8 }, false)`, `(U8AsBool { b: true }, false)`, `(U8AsBool { n: 0_u8 }, false)` and 1 more not covered
             (U8AsBool { b: true }, true) => {}
             (U8AsBool { b: false }, true) => {}
             (U8AsBool { n: 1.. }, true) => {}

tests/ui/pattern/usefulness/unions.stderr

@@ -16,11 +16,11 @@ LL ~             U8AsBool { n: 1.. } => {},
 LL +             U8AsBool { n: 0_u8 } | U8AsBool { b: false } => todo!()
    |
 
-error[E0004]: non-exhaustive patterns: `(U8AsBool { n: 0_u8 }, false)`, `(U8AsBool { b: false }, false)`, `(U8AsBool { n: 0_u8 }, false)` and 1 more not covered
+error[E0004]: non-exhaustive patterns: `(U8AsBool { n: 0_u8 }, false)`, `(U8AsBool { b: true }, false)`, `(U8AsBool { n: 0_u8 }, false)` and 1 more not covered
   --> $DIR/unions.rs:28:15
    |
 LL |         match (x, true) {
-   |               ^^^^^^^^^ patterns `(U8AsBool { n: 0_u8 }, false)`, `(U8AsBool { b: false }, false)`, `(U8AsBool { n: 0_u8 }, false)` and 1 more not covered
+   |               ^^^^^^^^^ patterns `(U8AsBool { n: 0_u8 }, false)`, `(U8AsBool { b: true }, false)`, `(U8AsBool { n: 0_u8 }, false)` and 1 more not covered
    |
    = note: the matched value is of type `(U8AsBool, bool)`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern as shown, or multiple match arms