Remove `TestCase::Irrefutable`

4 files changed, 38 insertions, 58 deletions

diff --git a/compiler/rustc_mir_build/src/builder/matches/match_pair.rs b/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
index 89d8189cee0..55487f48509 100644
--- a/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
@@ -116,24 +116,23 @@ impl<'tcx> MatchPairTree<'tcx> {
         }
 
         let place = place_builder.try_to_place(cx);
-        let default_irrefutable = || TestCase::Irrefutable {};
         let mut subpairs = Vec::new();
         let test_case = match pattern.kind {
-            PatKind::Wild | PatKind::Error(_) => default_irrefutable(),
+            PatKind::Wild | PatKind::Error(_) => None,
 
-            PatKind::Or { ref pats } => TestCase::Or {
+            PatKind::Or { ref pats } => Some(TestCase::Or {
                 pats: pats.iter().map(|pat| FlatPat::new(place_builder.clone(), pat, cx)).collect(),
-            },
+            }),
 
             PatKind::Range(ref range) => {
                 if range.is_full_range(cx.tcx) == Some(true) {
-                    default_irrefutable()
+                    None
                 } else {
-                    TestCase::Range(Arc::clone(range))
+                    Some(TestCase::Range(Arc::clone(range)))
                 }
             }
 
-            PatKind::Constant { value } => TestCase::Constant { value },
+            PatKind::Constant { value } => Some(TestCase::Constant { value }),
 
             PatKind::AscribeUserType {
                 ascription: Ascription { ref annotation, variance },
@@ -154,7 +153,7 @@ impl<'tcx> MatchPairTree<'tcx> {
                     extra_data.ascriptions.push(super::Ascription { source, annotation, variance });
                 }
 
-                default_irrefutable()
+                None
             }
 
             PatKind::Binding { mode, var, ref subpattern, .. } => {
@@ -199,12 +198,12 @@ impl<'tcx> MatchPairTree<'tcx> {
                     });
                 }
 
-                default_irrefutable()
+                None
             }
 
             PatKind::ExpandedConstant { subpattern: ref pattern, def_id: _, is_inline: false } => {
                 MatchPairTree::for_pattern(place_builder, pattern, cx, &mut subpairs, extra_data);
-                default_irrefutable()
+                None
             }
             PatKind::ExpandedConstant { subpattern: ref pattern, def_id, is_inline: true } => {
                 MatchPairTree::for_pattern(place_builder, pattern, cx, &mut subpairs, extra_data);
@@ -233,7 +232,7 @@ impl<'tcx> MatchPairTree<'tcx> {
                     extra_data.ascriptions.push(super::Ascription { annotation, source, variance });
                 }
 
-                default_irrefutable()
+                None
             }
 
             PatKind::Array { ref prefix, ref slice, ref suffix } => {
@@ -245,7 +244,7 @@ impl<'tcx> MatchPairTree<'tcx> {
                     slice,
                     suffix,
                 );
-                default_irrefutable()
+                None
             }
             PatKind::Slice { ref prefix, ref slice, ref suffix } => {
                 cx.prefix_slice_suffix(
@@ -258,12 +257,12 @@ impl<'tcx> MatchPairTree<'tcx> {
                 );
 
                 if prefix.is_empty() && slice.is_some() && suffix.is_empty() {
-                    default_irrefutable()
+                    None
                 } else {
-                    TestCase::Slice {
+                    Some(TestCase::Slice {
                         len: prefix.len() + suffix.len(),
                         variable_length: slice.is_some(),
-                    }
+                    })
                 }
             }
 
@@ -279,16 +278,12 @@ impl<'tcx> MatchPairTree<'tcx> {
                             .apply_ignore_module(cx.tcx, cx.infcx.typing_env(cx.param_env))
                 }) && (adt_def.did().is_local()
                     || !adt_def.is_variant_list_non_exhaustive());
-                if irrefutable {
-                    default_irrefutable()
-                } else {
-                    TestCase::Variant { adt_def, variant_index }
-                }
+                if irrefutable { None } else { Some(TestCase::Variant { adt_def, variant_index }) }
             }
 
             PatKind::Leaf { ref subpatterns } => {
                 cx.field_match_pairs(&mut subpairs, extra_data, place_builder, subpatterns);
-                default_irrefutable()
+                None
             }
 
             PatKind::Deref { ref subpattern } => {
@@ -299,7 +294,7 @@ impl<'tcx> MatchPairTree<'tcx> {
                     &mut subpairs,
                     extra_data,
                 );
-                default_irrefutable()
+                None
             }
 
             PatKind::DerefPattern { ref subpattern, mutability } => {
@@ -316,18 +311,25 @@ impl<'tcx> MatchPairTree<'tcx> {
                     &mut subpairs,
                     extra_data,
                 );
-                TestCase::Deref { temp, mutability }
+                Some(TestCase::Deref { temp, mutability })
             }
 
-            PatKind::Never => TestCase::Never,
+            PatKind::Never => Some(TestCase::Never),
         };
 
-        match_pairs.push(MatchPairTree {
-            place,
-            test_case,
-            subpairs,
-            pattern_ty: pattern.ty,
-            pattern_span: pattern.span,
-        });
+        if let Some(test_case) = test_case {
+            // This pattern is refutable, so push a new match-pair node.
+            match_pairs.push(MatchPairTree {
+                place,
+                test_case,
+                subpairs,
+                pattern_ty: pattern.ty,
+                pattern_span: pattern.span,
+            })
+        } else {
+            // This pattern is irrefutable, so it doesn't need its own match-pair node.
+            // Just push its refutable subpatterns instead, if any.
+            match_pairs.extend(subpairs);
+        }
     }
 }
diff --git a/compiler/rustc_mir_build/src/builder/matches/mod.rs b/compiler/rustc_mir_build/src/builder/matches/mod.rs
index 8c8f4c3c92c..bb93482c0b6 100644
--- a/compiler/rustc_mir_build/src/builder/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/mod.rs
@@ -1054,7 +1054,6 @@ struct Candidate<'tcx> {
     ///   (see [`Builder::test_remaining_match_pairs_after_or`]).
     ///
     /// Invariants:
-    /// - All [`TestCase::Irrefutable`] patterns have been removed by simplification.
     /// - All or-patterns ([`TestCase::Or`]) have been sorted to the end.
     match_pairs: Vec<MatchPairTree<'tcx>>,
 
@@ -1226,17 +1225,11 @@ struct Ascription<'tcx> {
 /// - [`Builder::pick_test_for_match_pair`] (to choose a test)
 /// - [`Builder::sort_candidate`] (to see how the test interacts with a match pair)
 ///
-/// Two variants are unlike the others and deserve special mention:
-///
-/// - [`Self::Irrefutable`] is only used temporarily when building a [`MatchPairTree`].
-///   They are then flattened away by [`Builder::simplify_match_pairs`], with any
-///   bindings/ascriptions incorporated into the enclosing [`FlatPat`].
-/// - [`Self::Or`] are not tested directly like the other variants. Instead they
-///   participate in or-pattern expansion, where they are transformed into subcandidates.
-///   - See [`Builder::expand_and_match_or_candidates`].
+/// Note that or-patterns are not tested directly like the other variants.
+/// Instead they participate in or-pattern expansion, where they are transformed into
+/// subcandidates. See [`Builder::expand_and_match_or_candidates`].
 #[derive(Debug, Clone)]
 enum TestCase<'tcx> {
-    Irrefutable {},
     Variant { adt_def: ty::AdtDef<'tcx>, variant_index: VariantIdx },
     Constant { value: mir::Const<'tcx> },
     Range(Arc<PatRange<'tcx>>),
@@ -1269,10 +1262,6 @@ pub(crate) struct MatchPairTree<'tcx> {
     place: Option<Place<'tcx>>,
 
     /// ... must pass this test...
-    ///
-    /// ---
-    /// Invariant: after creation and simplification in [`FlatPat::new`],
-    /// this must not be [`TestCase::Irrefutable`].
     test_case: TestCase<'tcx>,
 
     /// ... and these subpairs must match.
diff --git a/compiler/rustc_mir_build/src/builder/matches/simplify.rs b/compiler/rustc_mir_build/src/builder/matches/simplify.rs
index f4bcf62a4b1..5965b35b70c 100644
--- a/compiler/rustc_mir_build/src/builder/matches/simplify.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/simplify.rs
@@ -47,13 +47,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         // match lowering forces us to lower bindings inside or-patterns last.
         for mut match_pair in mem::take(match_pairs) {
             self.simplify_match_pairs(&mut match_pair.subpairs, extra_data);
-            if let TestCase::Irrefutable {} = match_pair.test_case {
-                // Simplifiable pattern; we replace it with its already simplified subpairs.
-                match_pairs.append(&mut match_pair.subpairs);
-            } else {
-                // Unsimplifiable pattern; we keep it.
-                match_pairs.push(match_pair);
-            }
+            // Unsimplifiable pattern; we keep it.
+            match_pairs.push(match_pair);
         }
 
         // Move or-patterns to the end, because they can result in us
diff --git a/compiler/rustc_mir_build/src/builder/matches/test.rs b/compiler/rustc_mir_build/src/builder/matches/test.rs
index a7a028bff97..fe5ec32422c 100644
--- a/compiler/rustc_mir_build/src/builder/matches/test.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/test.rs
@@ -55,12 +55,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             // Or-patterns are not tested directly; instead they are expanded into subcandidates,
             // which are then distinguished by testing whatever non-or patterns they contain.
             TestCase::Or { .. } => bug!("or-patterns should have already been handled"),
-
-            TestCase::Irrefutable { .. } => span_bug!(
-                match_pair.pattern_span,
-                "simplifiable pattern found: {:?}",
-                match_pair.pattern_span
-            ),
         };
 
         Test { span: match_pair.pattern_span, kind }