Rollup merge of #127858 - Zalathar:pair-tree, r=Nadrieril

match lowering: Rename `MatchPair` to `MatchPairTree`

In #120904, `MatchPair` became able to store other match pairs as children, forming a tree. That has made the old name confusing, so this patch renames the type to `MatchPairTree`.

This PR also includes a patch renaming the `test` method to `pick_test_for_match_pair`, since it would conflict with the main change.

r? `@Nadrieril`

5 files changed, 46 insertions, 39 deletions

diff --git a/compiler/rustc_mir_build/src/build/matches/match_pair.rs b/compiler/rustc_mir_build/src/build/matches/match_pair.rs
index 2f540478674..95fec154918 100644
--- a/compiler/rustc_mir_build/src/build/matches/match_pair.rs
+++ b/compiler/rustc_mir_build/src/build/matches/match_pair.rs
@@ -3,37 +3,37 @@ use rustc_middle::thir::{self, *};
 use rustc_middle::ty::{self, Ty, TypeVisitableExt};
 
 use crate::build::expr::as_place::{PlaceBase, PlaceBuilder};
-use crate::build::matches::{FlatPat, MatchPair, TestCase};
+use crate::build::matches::{FlatPat, MatchPairTree, TestCase};
 use crate::build::Builder;
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
-    /// Builds and returns [`MatchPair`] trees, one for each pattern in
+    /// Builds and returns [`MatchPairTree`] subtrees, one for each pattern in
     /// `subpatterns`, representing the fields of a [`PatKind::Variant`] or
     /// [`PatKind::Leaf`].
     ///
-    /// Used internally by [`MatchPair::new`].
+    /// Used internally by [`MatchPairTree::for_pattern`].
     fn field_match_pairs<'pat>(
         &mut self,
         place: PlaceBuilder<'tcx>,
         subpatterns: &'pat [FieldPat<'tcx>],
-    ) -> Vec<MatchPair<'pat, 'tcx>> {
+    ) -> Vec<MatchPairTree<'pat, 'tcx>> {
         subpatterns
             .iter()
             .map(|fieldpat| {
                 let place =
                     place.clone_project(PlaceElem::Field(fieldpat.field, fieldpat.pattern.ty));
-                MatchPair::new(place, &fieldpat.pattern, self)
+                MatchPairTree::for_pattern(place, &fieldpat.pattern, self)
             })
             .collect()
     }
 
-    /// Builds [`MatchPair`] trees for the prefix/middle/suffix parts of an
+    /// Builds [`MatchPairTree`] subtrees for the prefix/middle/suffix parts of an
     /// array pattern or slice pattern, and adds those trees to `match_pairs`.
     ///
-    /// Used internally by [`MatchPair::new`].
+    /// Used internally by [`MatchPairTree::for_pattern`].
     fn prefix_slice_suffix<'pat>(
         &mut self,
-        match_pairs: &mut Vec<MatchPair<'pat, 'tcx>>,
+        match_pairs: &mut Vec<MatchPairTree<'pat, 'tcx>>,
         place: &PlaceBuilder<'tcx>,
         prefix: &'pat [Box<Pat<'tcx>>],
         opt_slice: &'pat Option<Box<Pat<'tcx>>>,
@@ -52,7 +52,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         match_pairs.extend(prefix.iter().enumerate().map(|(idx, subpattern)| {
             let elem =
                 ProjectionElem::ConstantIndex { offset: idx as u64, min_length, from_end: false };
-            MatchPair::new(place.clone_project(elem), subpattern, self)
+            MatchPairTree::for_pattern(place.clone_project(elem), subpattern, self)
         }));
 
         if let Some(subslice_pat) = opt_slice {
@@ -62,7 +62,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 to: if exact_size { min_length - suffix_len } else { suffix_len },
                 from_end: !exact_size,
             });
-            match_pairs.push(MatchPair::new(subslice, subslice_pat, self));
+            match_pairs.push(MatchPairTree::for_pattern(subslice, subslice_pat, self));
         }
 
         match_pairs.extend(suffix.iter().rev().enumerate().map(|(idx, subpattern)| {
@@ -73,19 +73,19 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 from_end: !exact_size,
             };
             let place = place.clone_project(elem);
-            MatchPair::new(place, subpattern, self)
+            MatchPairTree::for_pattern(place, subpattern, self)
         }));
     }
 }
 
-impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
-    /// Recursively builds a `MatchPair` tree for the given pattern and its
+impl<'pat, 'tcx> MatchPairTree<'pat, 'tcx> {
+    /// Recursively builds a match pair tree for the given pattern and its
     /// subpatterns.
-    pub(in crate::build) fn new(
+    pub(in crate::build) fn for_pattern(
         mut place_builder: PlaceBuilder<'tcx>,
         pattern: &'pat Pat<'tcx>,
         cx: &mut Builder<'_, 'tcx>,
-    ) -> MatchPair<'pat, 'tcx> {
+    ) -> MatchPairTree<'pat, 'tcx> {
         // Force the place type to the pattern's type.
         // FIXME(oli-obk): can we use this to simplify slice/array pattern hacks?
         if let Some(resolved) = place_builder.resolve_upvar(cx) {
@@ -138,7 +138,7 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
                     variance,
                 });
 
-                subpairs.push(MatchPair::new(place_builder, subpattern, cx));
+                subpairs.push(MatchPairTree::for_pattern(place_builder, subpattern, cx));
                 TestCase::Irrefutable { ascription, binding: None }
             }
 
@@ -152,7 +152,7 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
 
                 if let Some(subpattern) = subpattern.as_ref() {
                     // this is the `x @ P` case; have to keep matching against `P` now
-                    subpairs.push(MatchPair::new(place_builder, subpattern, cx));
+                    subpairs.push(MatchPairTree::for_pattern(place_builder, subpattern, cx));
                 }
                 TestCase::Irrefutable { ascription: None, binding }
             }
@@ -182,7 +182,7 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
                     super::Ascription { annotation, source, variance: ty::Contravariant }
                 });
 
-                subpairs.push(MatchPair::new(place_builder, pattern, cx));
+                subpairs.push(MatchPairTree::for_pattern(place_builder, pattern, cx));
                 TestCase::Irrefutable { ascription, binding: None }
             }
 
@@ -231,7 +231,7 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
             }
 
             PatKind::Deref { ref subpattern } => {
-                subpairs.push(MatchPair::new(place_builder.deref(), subpattern, cx));
+                subpairs.push(MatchPairTree::for_pattern(place_builder.deref(), subpattern, cx));
                 default_irrefutable()
             }
 
@@ -242,13 +242,17 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
                     Ty::new_ref(cx.tcx, cx.tcx.lifetimes.re_erased, subpattern.ty, mutability),
                     pattern.span,
                 );
-                subpairs.push(MatchPair::new(PlaceBuilder::from(temp).deref(), subpattern, cx));
+                subpairs.push(MatchPairTree::for_pattern(
+                    PlaceBuilder::from(temp).deref(),
+                    subpattern,
+                    cx,
+                ));
                 TestCase::Deref { temp, mutability }
             }
 
             PatKind::Never => TestCase::Never,
         };
 
-        MatchPair { place, test_case, subpairs, pattern }
+        MatchPairTree { place, test_case, subpairs, pattern }
     }
 }
diff --git a/compiler/rustc_mir_build/src/build/matches/mod.rs b/compiler/rustc_mir_build/src/build/matches/mod.rs
index 20c33745af8..b531a392efa 100644
--- a/compiler/rustc_mir_build/src/build/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/build/matches/mod.rs
@@ -1032,15 +1032,15 @@ impl<'tcx> PatternExtraData<'tcx> {
 #[derive(Debug, Clone)]
 struct FlatPat<'pat, 'tcx> {
     /// To match the pattern, all of these must be satisfied...
-    // Invariant: all the `MatchPair`s are recursively simplified.
+    // Invariant: all the match pairs are recursively simplified.
     // Invariant: or-patterns must be sorted to the end.
-    match_pairs: Vec<MatchPair<'pat, 'tcx>>,
+    match_pairs: Vec<MatchPairTree<'pat, 'tcx>>,
 
     extra_data: PatternExtraData<'tcx>,
 }
 
 impl<'tcx, 'pat> FlatPat<'pat, 'tcx> {
-    /// Creates a `FlatPat` containing a simplified [`MatchPair`] list/forest
+    /// Creates a `FlatPat` containing a simplified [`MatchPairTree`] list/forest
     /// for the given pattern.
     fn new(
         place: PlaceBuilder<'tcx>,
@@ -1048,7 +1048,7 @@ impl<'tcx, 'pat> FlatPat<'pat, 'tcx> {
         cx: &mut Builder<'_, 'tcx>,
     ) -> Self {
         // First, recursively build a tree of match pairs for the given pattern.
-        let mut match_pairs = vec![MatchPair::new(place, pattern, cx)];
+        let mut match_pairs = vec![MatchPairTree::for_pattern(place, pattern, cx)];
         let mut extra_data = PatternExtraData {
             span: pattern.span,
             bindings: Vec::new(),
@@ -1065,9 +1065,9 @@ impl<'tcx, 'pat> FlatPat<'pat, 'tcx> {
 #[derive(Debug)]
 struct Candidate<'pat, 'tcx> {
     /// For the candidate to match, all of these must be satisfied...
-    // Invariant: all the `MatchPair`s are recursively simplified.
+    // Invariant: all the match pairs are recursively simplified.
     // Invariant: or-patterns must be sorted at the end.
-    match_pairs: Vec<MatchPair<'pat, 'tcx>>,
+    match_pairs: Vec<MatchPairTree<'pat, 'tcx>>,
 
     /// ...and if this is non-empty, one of these subcandidates also has to match...
     // Invariant: at the end of the algorithm, this must never contain a `is_never` candidate
@@ -1126,7 +1126,7 @@ impl<'tcx, 'pat> Candidate<'pat, 'tcx> {
 
     /// Returns whether the first match pair of this candidate is an or-pattern.
     fn starts_with_or_pattern(&self) -> bool {
-        matches!(&*self.match_pairs, [MatchPair { test_case: TestCase::Or { .. }, .. }, ..])
+        matches!(&*self.match_pairs, [MatchPairTree { test_case: TestCase::Or { .. }, .. }, ..])
     }
 
     /// Visit the leaf candidates (those with no subcandidates) contained in
@@ -1206,7 +1206,7 @@ impl<'pat, 'tcx> TestCase<'pat, 'tcx> {
 /// Each node also has a list of subpairs (possibly empty) that must also match,
 /// and a reference to the THIR pattern it represents.
 #[derive(Debug, Clone)]
-pub(crate) struct MatchPair<'pat, 'tcx> {
+pub(crate) struct MatchPairTree<'pat, 'tcx> {
     /// This place...
     ///
     /// ---
@@ -1629,7 +1629,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     fn create_or_subcandidates<'pat>(
         &mut self,
         candidate: &mut Candidate<'pat, 'tcx>,
-        match_pair: MatchPair<'pat, 'tcx>,
+        match_pair: MatchPairTree<'pat, 'tcx>,
     ) {
         let TestCase::Or { pats } = match_pair.test_case else { bug!() };
         debug!("expanding or-pattern: candidate={:#?}\npats={:#?}", candidate, pats);
@@ -1813,8 +1813,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// [`Range`]: TestKind::Range
     fn pick_test(&mut self, candidates: &[&mut Candidate<'_, 'tcx>]) -> (Place<'tcx>, Test<'tcx>) {
         // Extract the match-pair from the highest priority candidate
-        let match_pair = &candidates.first().unwrap().match_pairs[0];
-        let test = self.test(match_pair);
+        let match_pair = &candidates[0].match_pairs[0];
+        let test = self.pick_test_for_match_pair(match_pair);
         // Unwrap is ok after simplification.
         let match_place = match_pair.place.unwrap();
         debug!(?test, ?match_pair);
diff --git a/compiler/rustc_mir_build/src/build/matches/simplify.rs b/compiler/rustc_mir_build/src/build/matches/simplify.rs
index 543301c71a0..20310f60821 100644
--- a/compiler/rustc_mir_build/src/build/matches/simplify.rs
+++ b/compiler/rustc_mir_build/src/build/matches/simplify.rs
@@ -12,7 +12,7 @@
 //! sort of test: for example, testing which variant an enum is, or
 //! testing a value against a constant.
 
-use crate::build::matches::{MatchPair, PatternExtraData, TestCase};
+use crate::build::matches::{MatchPairTree, PatternExtraData, TestCase};
 use crate::build::Builder;
 use tracing::{debug, instrument};
 
@@ -24,7 +24,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     #[instrument(skip(self), level = "debug")]
     pub(super) fn simplify_match_pairs<'pat>(
         &mut self,
-        match_pairs: &mut Vec<MatchPair<'pat, 'tcx>>,
+        match_pairs: &mut Vec<MatchPairTree<'pat, 'tcx>>,
         extra_data: &mut PatternExtraData<'tcx>,
     ) {
         // In order to please the borrow checker, in a pattern like `x @ pat` we must lower the
diff --git a/compiler/rustc_mir_build/src/build/matches/test.rs b/compiler/rustc_mir_build/src/build/matches/test.rs
index 5aed2537750..8a02ea1a06d 100644
--- a/compiler/rustc_mir_build/src/build/matches/test.rs
+++ b/compiler/rustc_mir_build/src/build/matches/test.rs
@@ -5,7 +5,7 @@
 // identify what tests are needed, perform the tests, and then filter
 // the candidates based on the result.
 
-use crate::build::matches::{Candidate, MatchPair, Test, TestBranch, TestCase, TestKind};
+use crate::build::matches::{Candidate, MatchPairTree, Test, TestBranch, TestCase, TestKind};
 use crate::build::Builder;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_hir::{LangItem, RangeEnd};
@@ -26,7 +26,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// Identifies what test is needed to decide if `match_pair` is applicable.
     ///
     /// It is a bug to call this with a not-fully-simplified pattern.
-    pub(super) fn test<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> Test<'tcx> {
+    pub(super) fn pick_test_for_match_pair<'pat>(
+        &mut self,
+        match_pair: &MatchPairTree<'pat, 'tcx>,
+    ) -> Test<'tcx> {
         let kind = match match_pair.test_case {
             TestCase::Variant { adt_def, variant_index: _ } => TestKind::Switch { adt_def },
 
diff --git a/compiler/rustc_mir_build/src/build/matches/util.rs b/compiler/rustc_mir_build/src/build/matches/util.rs
index e67fc843285..8fe8069b345 100644
--- a/compiler/rustc_mir_build/src/build/matches/util.rs
+++ b/compiler/rustc_mir_build/src/build/matches/util.rs
@@ -1,7 +1,7 @@
 use std::marker::PhantomData;
 
 use crate::build::expr::as_place::PlaceBase;
-use crate::build::matches::{Binding, Candidate, FlatPat, MatchPair, TestCase};
+use crate::build::matches::{Binding, Candidate, FlatPat, MatchPairTree, TestCase};
 use crate::build::Builder;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_middle::mir::*;
@@ -152,7 +152,7 @@ impl<'a, 'b, 'tcx> FakeBorrowCollector<'a, 'b, 'tcx> {
         }
     }
 
-    fn visit_match_pair(&mut self, match_pair: &MatchPair<'_, 'tcx>) {
+    fn visit_match_pair(&mut self, match_pair: &MatchPairTree<'_, 'tcx>) {
         if let TestCase::Or { pats, .. } = &match_pair.test_case {
             for flat_pat in pats.iter() {
                 self.visit_flat_pat(flat_pat)
@@ -260,7 +260,7 @@ where
         }
     }
 
-    fn visit_match_pair(&mut self, match_pair: &MatchPair<'_, 'tcx>) {
+    fn visit_match_pair(&mut self, match_pair: &MatchPairTree<'_, 'tcx>) {
         if let TestCase::Or { pats, .. } = &match_pair.test_case {
             // All the or-alternatives should bind the same locals, so we only visit the first one.
             self.visit_flat_pat(&pats[0])