Auto merge of #119581 - Nadrieril:detangle-arena, r=<try>

Exhaustiveness: remove the need for arena-allocation within the algorithm

WARNING: skip the first commit, it's from #119329 which is getting merged.

This nicely cleans up the lifetime story: after this PR, all the `&'p DeconstructedPat` ever handled in the algorithm are coming from user input; we never build one ourselves.

r? `@compiler-errors`

Author: bors

Cargo.lock

@@ -4355,7 +4355,6 @@ dependencies = [
  "rustc_target",
  "smallvec",
  "tracing",
- "typed-arena",
 ]
 
 [[package]]
@@ -5692,12 +5691,6 @@ dependencies = [
  "rustc-hash",
 ]
 
-[[package]]
-name = "typed-arena"
-version = "2.0.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6af6ae20167a9ece4bcb41af5b80f8a1f1df981f6391189ce00fd257af04126a"
-
 [[package]]
 name = "typenum"
 version = "1.16.0"

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -554,7 +554,7 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
         let cx = self.new_cx(refutability, None, scrut, pat.span);
         let pat = self.lower_pattern(&cx, pat)?;
         let arms = [MatchArm { pat, arm_data: self.lint_level, has_guard: false }];
-        let report = analyze_match(&cx, &arms, pat.ty());
+        let report = analyze_match(&cx, &arms, pat.ty().inner());
         Ok((cx, report))
     }
 
@@ -972,7 +972,7 @@ fn report_non_exhaustive_match<'p, 'tcx>(
                 }
             } else if ty == cx.tcx.types.str_ {
                 err.note("`&str` cannot be matched exhaustively, so a wildcard `_` is necessary");
-            } else if cx.is_foreign_non_exhaustive_enum(ty) {
+            } else if cx.is_foreign_non_exhaustive_enum(cx.reveal_opaque_ty(ty)) {
                 err.note(format!("`{ty}` is marked as non-exhaustive, so a wildcard `_` is necessary to match exhaustively"));
             }
         }
@@ -1112,12 +1112,12 @@ fn collect_non_exhaustive_tys<'tcx>(
     non_exhaustive_tys: &mut FxIndexSet<Ty<'tcx>>,
 ) {
     if matches!(pat.ctor(), Constructor::NonExhaustive) {
-        non_exhaustive_tys.insert(pat.ty());
+        non_exhaustive_tys.insert(pat.ty().inner());
     }
     if let Constructor::IntRange(range) = pat.ctor() {
         if cx.is_range_beyond_boundaries(range, pat.ty()) {
             // The range denotes the values before `isize::MIN` or the values after `usize::MAX`/`isize::MAX`.
-            non_exhaustive_tys.insert(pat.ty());
+            non_exhaustive_tys.insert(pat.ty().inner());
         }
     }
     pat.iter_fields()

compiler/rustc_pattern_analysis/Cargo.toml

@@ -20,7 +20,6 @@ rustc_span = { path = "../rustc_span", optional = true }
 rustc_target = { path = "../rustc_target", optional = true }
 smallvec = { version = "1.8.1", features = ["union"] }
 tracing = "0.1"
-typed-arena = { version = "2.0.2", optional = true }
 # tidy-alphabetical-end
 
 [features]
@@ -41,6 +40,3 @@ rustc = [
     "smallvec/may_dangle",
     "rustc_index/nightly",
 ]
-stable = [
-    "dep:typed-arena",
-]

compiler/rustc_pattern_analysis/src/constructor.rs

@@ -718,7 +718,7 @@ impl<Cx: TypeCx> Constructor<Cx> {
 
     /// The number of fields for this constructor. This must be kept in sync with
     /// `Fields::wildcards`.
-    pub(crate) fn arity(&self, pcx: &PlaceCtxt<'_, '_, Cx>) -> usize {
+    pub(crate) fn arity(&self, pcx: &PlaceCtxt<'_, Cx>) -> usize {
         pcx.ctor_arity(self)
     }
 
@@ -727,7 +727,7 @@ impl<Cx: TypeCx> Constructor<Cx> {
     /// this checks for inclusion.
     // We inline because this has a single call site in `Matrix::specialize_constructor`.
     #[inline]
-    pub(crate) fn is_covered_by<'p>(&self, pcx: &PlaceCtxt<'_, 'p, Cx>, other: &Self) -> bool {
+    pub(crate) fn is_covered_by(&self, pcx: &PlaceCtxt<'_, Cx>, other: &Self) -> bool {
         match (self, other) {
             (Wildcard, _) => pcx
                 .mcx
@@ -861,7 +861,7 @@ impl<Cx: TypeCx> ConstructorSet<Cx> {
     #[instrument(level = "debug", skip(self, pcx, ctors), ret)]
     pub(crate) fn split<'a>(
         &self,
-        pcx: &PlaceCtxt<'a, '_, Cx>,
+        pcx: &PlaceCtxt<'a, Cx>,
         ctors: impl Iterator<Item = &'a Constructor<Cx>> + Clone,
     ) -> SplitConstructorSet<Cx> {
         let mut present: SmallVec<[_; 1]> = SmallVec::new();

compiler/rustc_pattern_analysis/src/lib.rs

@@ -36,13 +36,6 @@ use crate::rustc::RustcMatchCheckCtxt;
 #[cfg(feature = "rustc")]
 use crate::usefulness::{compute_match_usefulness, ValidityConstraint};
 
-// It's not possible to only enable the `typed_arena` dependency when the `rustc` feature is off, so
-// we use another feature instead. The crate won't compile if one of these isn't enabled.
-#[cfg(feature = "rustc")]
-pub(crate) use rustc_arena::TypedArena;
-#[cfg(feature = "stable")]
-pub(crate) use typed_arena::Arena as TypedArena;
-
 pub trait Captures<'a> {}
 impl<'a, T: ?Sized> Captures<'a> for T {}
 
@@ -61,8 +54,6 @@ pub trait TypeCx: Sized + fmt::Debug {
     /// Extra data to store in a pattern.
     type PatData: Clone;
 
-    /// FIXME(Nadrieril): `Cx` should only give us revealed types.
-    fn reveal_opaque_ty(&self, ty: Self::Ty) -> Self::Ty;
     fn is_exhaustive_patterns_feature_on(&self) -> bool;
 
     /// The number of fields for this constructor.
@@ -87,11 +78,9 @@ pub trait TypeCx: Sized + fmt::Debug {
 /// Context that provides information global to a match.
 #[derive(derivative::Derivative)]
 #[derivative(Clone(bound = ""), Copy(bound = ""))]
-pub struct MatchCtxt<'a, 'p, Cx: TypeCx> {
+pub struct MatchCtxt<'a, Cx: TypeCx> {
     /// The context for type information.
     pub tycx: &'a Cx,
-    /// An arena to store the wildcards we produce during analysis.
-    pub wildcard_arena: &'p TypedArena<DeconstructedPat<'p, Cx>>,
 }
 
 /// The arm of a match expression.
@@ -112,10 +101,9 @@ pub fn analyze_match<'p, 'tcx>(
     arms: &[rustc::MatchArm<'p, 'tcx>],
     scrut_ty: Ty<'tcx>,
 ) -> rustc::UsefulnessReport<'p, 'tcx> {
-    // Arena to store the extra wildcards we construct during analysis.
-    let wildcard_arena = tycx.pattern_arena;
+    let scrut_ty = tycx.reveal_opaque_ty(scrut_ty);
     let scrut_validity = ValidityConstraint::from_bool(tycx.known_valid_scrutinee);
-    let cx = MatchCtxt { tycx, wildcard_arena };
+    let cx = MatchCtxt { tycx };
 
     let report = compute_match_usefulness(cx, arms, scrut_ty, scrut_validity);
 

compiler/rustc_pattern_analysis/src/lints.rs

@@ -1,7 +1,7 @@
 use smallvec::SmallVec;
 
 use rustc_data_structures::captures::Captures;
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty;
 use rustc_session::lint;
 use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
 use rustc_span::Span;
@@ -11,11 +11,11 @@ use crate::errors::{
     NonExhaustiveOmittedPattern, NonExhaustiveOmittedPatternLintOnArm, Overlap,
     OverlappingRangeEndpoints, Uncovered,
 };
+use crate::pat::PatOrWild;
 use crate::rustc::{
-    Constructor, DeconstructedPat, MatchArm, MatchCtxt, PlaceCtxt, RustcMatchCheckCtxt,
+    Constructor, DeconstructedPat, MatchArm, MatchCtxt, PlaceCtxt, RevealedTy, RustcMatchCheckCtxt,
     SplitConstructorSet, WitnessPat,
 };
-use crate::TypeCx;
 
 /// A column of patterns in the matrix, where a column is the intuitive notion of "subpatterns that
 /// inspect the same subvalue/place".
@@ -34,28 +34,24 @@ pub(crate) struct PatternColumn<'p, 'tcx> {
 
 impl<'p, 'tcx> PatternColumn<'p, 'tcx> {
     pub(crate) fn new(arms: &[MatchArm<'p, 'tcx>]) -> Self {
-        let mut patterns = Vec::with_capacity(arms.len());
+        let mut column = PatternColumn { patterns: Vec::with_capacity(arms.len()) };
         for arm in arms {
-            if arm.pat.is_or_pat() {
-                patterns.extend(arm.pat.flatten_or_pat())
-            } else {
-                patterns.push(arm.pat)
-            }
+            column.expand_and_push(PatOrWild::Pat(arm.pat));
         }
-        Self { patterns }
-    }
-
-    fn is_empty(&self) -> bool {
-        self.patterns.is_empty()
+        column
     }
-    fn head_ty(&self, cx: MatchCtxt<'_, 'p, 'tcx>) -> Option<Ty<'tcx>> {
-        if self.patterns.len() == 0 {
-            return None;
+    fn expand_and_push(&mut self, pat: PatOrWild<'p, RustcMatchCheckCtxt<'p, 'tcx>>) {
+        if pat.is_or_pat() {
+            self.patterns.extend(
+                pat.flatten_or_pat().into_iter().filter_map(|pat_or_wild| pat_or_wild.as_pat()),
+            )
+        } else if let Some(pat) = pat.as_pat() {
+            self.patterns.push(pat)
         }
+    }
 
-        let ty = self.patterns[0].ty();
-        // FIXME(Nadrieril): `Cx` should only give us revealed types.
-        Some(cx.tycx.reveal_opaque_ty(ty))
+    fn head_ty(&self) -> Option<RevealedTy<'tcx>> {
+        self.patterns.first().map(|pat| pat.ty())
     }
 
     /// Do constructor splitting on the constructors of the column.
@@ -91,21 +87,11 @@ impl<'p, 'tcx> PatternColumn<'p, 'tcx> {
         let relevant_patterns =
             self.patterns.iter().filter(|pat| ctor.is_covered_by(pcx, pat.ctor()));
         for pat in relevant_patterns {
-            let specialized = pat.specialize(pcx, ctor);
-            for (subpat, column) in specialized.iter().zip(&mut specialized_columns) {
-                if subpat.is_or_pat() {
-                    column.patterns.extend(subpat.flatten_or_pat())
-                } else {
-                    column.patterns.push(subpat)
-                }
+            let specialized = pat.specialize(ctor, pcx.ctor_arity(ctor));
+            for (subpat, column) in specialized.into_iter().zip(&mut specialized_columns) {
+                column.expand_and_push(subpat);
             }
         }
-
-        assert!(
-            !specialized_columns[0].is_empty(),
-            "ctor {ctor:?} was listed as present but isn't;
-            there is an inconsistency between `Constructor::is_covered_by` and `ConstructorSet::split`"
-        );
         specialized_columns
     }
 }
@@ -117,7 +103,7 @@ fn collect_nonexhaustive_missing_variants<'a, 'p, 'tcx>(
     cx: MatchCtxt<'a, 'p, 'tcx>,
     column: &PatternColumn<'p, 'tcx>,
 ) -> Vec<WitnessPat<'p, 'tcx>> {
-    let Some(ty) = column.head_ty(cx) else {
+    let Some(ty) = column.head_ty() else {
         return Vec::new();
     };
     let pcx = &PlaceCtxt::new_dummy(cx, ty);
@@ -164,7 +150,7 @@ pub(crate) fn lint_nonexhaustive_missing_variants<'a, 'p, 'tcx>(
     cx: MatchCtxt<'a, 'p, 'tcx>,
     arms: &[MatchArm<'p, 'tcx>],
     pat_column: &PatternColumn<'p, 'tcx>,
-    scrut_ty: Ty<'tcx>,
+    scrut_ty: RevealedTy<'tcx>,
 ) {
     let rcx: &RustcMatchCheckCtxt<'_, '_> = cx.tycx;
     if !matches!(
@@ -182,7 +168,7 @@ pub(crate) fn lint_nonexhaustive_missing_variants<'a, 'p, 'tcx>(
                 rcx.match_lint_level,
                 rcx.scrut_span,
                 NonExhaustiveOmittedPattern {
-                    scrut_ty,
+                    scrut_ty: scrut_ty.inner(),
                     uncovered: Uncovered::new(rcx.scrut_span, rcx, witnesses),
                 },
             );
@@ -218,7 +204,7 @@ pub(crate) fn lint_overlapping_range_endpoints<'a, 'p, 'tcx>(
     cx: MatchCtxt<'a, 'p, 'tcx>,
     column: &PatternColumn<'p, 'tcx>,
 ) {
-    let Some(ty) = column.head_ty(cx) else {
+    let Some(ty) = column.head_ty() else {
         return;
     };
     let pcx = &PlaceCtxt::new_dummy(cx, ty);