Add barest-bones deref patterns

Co-authored-by: Deadbeef <[email protected]>

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -413,7 +413,10 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
  }
  }
  PatKind::Box(..) => {
- gate!(&self, box_patterns, pattern.span, "box pattern syntax is experimental");
+ if !self.features.deref_patterns {
+ // Allow box patterns under `deref_patterns`.
+ gate!(&self, box_patterns, pattern.span, "box pattern syntax is experimental");
+ }
  }
  PatKind::Range(_, Some(_), Spanned { node: RangeEnd::Excluded, .. }) => {
  gate!(
@@ -607,13 +610,16 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
  };
  }
 
+ if !visitor.features.deref_patterns {
+ // Allow box patterns under `deref_patterns`.
+ gate_all_legacy_dont_use!(box_patterns, "box pattern syntax is experimental");
+ }
  gate_all_legacy_dont_use!(trait_alias, "trait aliases are experimental");
  // Despite being a new feature, `where T: Trait<Assoc(): Sized>`, which is RTN syntax now,
  // used to be gated under associated_type_bounds, which are right above, so RTN needs to
  // be too.
  gate_all_legacy_dont_use!(return_type_notation, "return type notation is experimental");
  gate_all_legacy_dont_use!(decl_macro, "`macro` is experimental");
- gate_all_legacy_dont_use!(box_patterns, "box pattern syntax is experimental");
  gate_all_legacy_dont_use!(
  exclusive_range_pattern,
  "exclusive range pattern syntax is experimental"

compiler/rustc_feature/src/unstable.rs

@@ -436,6 +436,8 @@ declare_features! (
  (unstable, deprecated_safe, "1.61.0", Some(94978)),
  /// Allows having using `suggestion` in the `#[deprecated]` attribute.
  (unstable, deprecated_suggestion, "1.61.0", Some(94785)),
+ /// Allows deref patterns.
+ (incomplete, deref_patterns, "CURRENT_RUSTC_VERSION", Some(87121)),
  /// Controls errors in trait implementations.
  (unstable, do_not_recommend, "1.67.0", Some(51992)),
  /// Tells rustdoc to automatically generate `#[doc(cfg(...))]`.

compiler/rustc_hir_typeck/src/pat.rs

@@ -18,8 +18,7 @@ use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::hygiene::DesugaringKind;
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym, Ident};
-use rustc_span::Span;
-use rustc_span::{BytePos, DUMMY_SP};
+use rustc_span::{BytePos, Span, DUMMY_SP};
 use rustc_target::abi::FieldIdx;
 use rustc_trait_selection::traits::{ObligationCause, Pattern};
 use ty::VariantDef;
@@ -211,6 +210,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  PatKind::Tuple(elements, ddpos) => {
  self.check_pat_tuple(pat.span, elements, ddpos, expected, pat_info)
  }
+ PatKind::Box(inner) if self.tcx.features().deref_patterns => {
+ self.check_pat_deref(pat.span, inner, expected, pat_info)
+ }
  PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, pat_info),
  PatKind::Ref(inner, mutbl) => self.check_pat_ref(pat, inner, mutbl, expected, pat_info),
  PatKind::Slice(before, slice, after) => {
@@ -1975,6 +1977,28 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  box_ty
  }
 
+ fn check_pat_deref(
+ &self,
+ span: Span,
+ inner: &'tcx Pat<'tcx>,
+ expected: Ty<'tcx>,
+ pat_info: PatInfo<'tcx, '_>,
+ ) -> Ty<'tcx> {
+ let tcx = self.tcx;
+ // FIXME(deref_patterns): use `DerefPure` for soundness
+ // FIXME(deref_patterns): use `DerefMut` when required
+ // <expected as Deref>::Target
+ let ty = Ty::new_projection(
+ tcx,
+ tcx.require_lang_item(hir::LangItem::DerefTarget, Some(span)),
+ [expected],
+ );
+ let ty = self.normalize(span, ty);
+ let ty = self.try_structurally_resolve_type(span, ty);
+ self.check_pat(inner, ty, pat_info);
+ expected
+ }
+
  // Precondition: Pat is Ref(inner)
  fn check_pat_ref(
  &self,

compiler/rustc_middle/src/thir.rs

@@ -647,6 +647,7 @@ impl<'tcx> Pat<'tcx> {
  AscribeUserType { subpattern, .. }
  | Binding { subpattern: Some(subpattern), .. }
  | Deref { subpattern }
+ | DerefPattern { subpattern }
  | InlineConstant { subpattern, .. } => subpattern.walk_(it),
  Leaf { subpatterns } | Variant { subpatterns, .. } => {
  subpatterns.iter().for_each(|field| field.pattern.walk_(it))
@@ -762,6 +763,11 @@ pub enum PatKind<'tcx> {
  subpattern: Box<Pat<'tcx>>,
  },
 
+ /// Deref pattern, written `box P` for now.
+ DerefPattern {
+ subpattern: Box<Pat<'tcx>>,
+ },
+
  /// One of the following:
  /// * `&str` (represented as a valtree), which will be handled as a string pattern and thus
  /// exhaustiveness checking will detect if you use the same string twice in different
@@ -1172,6 +1178,9 @@ impl<'tcx> fmt::Display for Pat<'tcx> {
  }
  write!(f, "{subpattern}")
  }
+ PatKind::DerefPattern { ref subpattern } => {
+ write!(f, "k#deref {subpattern}")
+ }
  PatKind::Constant { value } => write!(f, "{value}"),
  PatKind::InlineConstant { def: _, ref subpattern } => {
  write!(f, "{} (from inline const)", subpattern)

compiler/rustc_middle/src/thir/visit.rs

@@ -229,6 +229,7 @@ pub fn walk_pat<'thir, 'tcx: 'thir, V: Visitor<'thir, 'tcx>>(
  match &pat.kind {
  AscribeUserType { subpattern, ascription: _ }
  | Deref { subpattern }
+ | DerefPattern { subpattern }
  | Binding {
  subpattern: Some(subpattern),
  mutability: _,

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -879,6 +879,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  self.visit_primary_bindings(subpattern, pattern_user_ty.deref(), f);
  }
 
+ PatKind::DerefPattern { ref subpattern } => {
+ self.visit_primary_bindings(subpattern, UserTypeProjections::none(), f);
+ }
+
  PatKind::AscribeUserType {
  ref subpattern,
  ascription: thir::Ascription { ref annotation, variance: _ },

compiler/rustc_mir_build/src/build/matches/util.rs

@@ -256,6 +256,12 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
  subpairs.push(MatchPair::new(place_builder, subpattern, cx));
  default_irrefutable()
  }
+
+ PatKind::DerefPattern { .. } => {
+ // FIXME(deref_patterns)
+ // Treat it like a wildcard for now.
+ default_irrefutable()
+ }
  };
 
  MatchPair { place, test_case, subpairs, pattern }

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -250,6 +250,7 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
  | PatKind::Variant { .. }
  | PatKind::Leaf { .. }
  | PatKind::Deref { .. }
+ | PatKind::DerefPattern { .. }
  | PatKind::Range { .. }
  | PatKind::Slice { .. }
  | PatKind::Array { .. } => {
@@ -310,7 +311,7 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
  }
  visit::walk_pat(self, pat);
  }
- PatKind::Deref { .. } => {
+ PatKind::Deref { .. } | PatKind::DerefPattern { .. } => {
  let old_inside_adt = std::mem::replace(&mut self.inside_adt, false);
  visit::walk_pat(self, pat);
  self.inside_adt = old_inside_adt;

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

@@ -257,6 +257,9 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
  return self.lower_path(qpath, pat.hir_id, pat.span);
  }
 
+ hir::PatKind::Box(subpattern) if self.tcx.features().deref_patterns => {
+ PatKind::DerefPattern { subpattern: self.lower_pattern(subpattern) }
+ }
  hir::PatKind::Ref(subpattern, _) | hir::PatKind::Box(subpattern) => {
  PatKind::Deref { subpattern: self.lower_pattern(subpattern) }
  }

compiler/rustc_mir_build/src/thir/print.rs

@@ -688,6 +688,12 @@ impl<'a, 'tcx> ThirPrinter<'a, 'tcx> {
  self.print_pat(subpattern, depth_lvl + 2);
  print_indented!(self, "}", depth_lvl + 1);
  }
+ PatKind::DerefPattern { subpattern } => {
+ print_indented!(self, "DerefPattern { ", depth_lvl + 1);
+ print_indented!(self, "subpattern:", depth_lvl + 2);
+ self.print_pat(subpattern, depth_lvl + 2);
+ print_indented!(self, "}", depth_lvl + 1);
+ }
  PatKind::Constant { value } => {
  print_indented!(self, "Constant {", depth_lvl + 1);
  print_indented!(self, format!("value: {:?}", value), depth_lvl + 2);

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -462,6 +462,12 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
  _ => bug!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, ty),
  };
  }
+ PatKind::DerefPattern { .. } => {
+ // FIXME(deref_patterns): At least detect that `box _` is irrefutable.
+ fields = vec![];
+ arity = 0;
+ ctor = Opaque(OpaqueId::new());
+ }
  PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
  match ty.kind() {
  ty::Tuple(fs) => {

compiler/rustc_span/src/symbol.rs

@@ -674,6 +674,7 @@ symbols! {
  deref_method,
  deref_mut,
  deref_mut_method,
+ deref_patterns,
  deref_target,
  derive,
  derive_const,

tests/ui/cfg/cfg-false-feature.stderr

@@ -1,15 +1,3 @@
-warning: trait aliases are experimental
- --> $DIR/cfg-false-feature.rs:12:1
- |
-LL | trait A = Clone;
- | ^^^^^^^^^^^^^^^^
- |
- = note: see issue #41517 <https://github.com/rust-lang/rust/issues/41517> for more information
- = help: add `#![feature(trait_alias)]` to the crate attributes to enable
- = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
- = warning: unstable syntax can change at any point in the future, causing a hard error!
- = note: for more information, see issue #65860 <https://github.com/rust-lang/rust/issues/65860>
-
 warning: box pattern syntax is experimental
  --> $DIR/cfg-false-feature.rs:16:9
  |
@@ -22,5 +10,17 @@ LL | let box _ = Box::new(0);
  = warning: unstable syntax can change at any point in the future, causing a hard error!
  = note: for more information, see issue #65860 <https://github.com/rust-lang/rust/issues/65860>
 
+warning: trait aliases are experimental
+ --> $DIR/cfg-false-feature.rs:12:1
+ |
+LL | trait A = Clone;
+ | ^^^^^^^^^^^^^^^^
+ |
+ = note: see issue #41517 <https://github.com/rust-lang/rust/issues/41517> for more information
+ = help: add `#![feature(trait_alias)]` to the crate attributes to enable
+ = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+ = warning: unstable syntax can change at any point in the future, causing a hard error!
+ = note: for more information, see issue #65860 <https://github.com/rust-lang/rust/issues/65860>
+
 warning: 2 warnings emitted
 

tests/ui/feature-gates/feature-gate-deref_patterns.rs

@@ -0,0 +1,9 @@
+fn main() {
+ // We reuse the `box` syntax so this doesn't actually test the feature gate but eh.
+ let box x = Box::new('c'); //~ ERROR box pattern syntax is experimental
+ println!("x: {}", x);
+
+ // `box` syntax is allowed to be cfg-ed out for historical reasons (#65742).
+ #[cfg(FALSE)]
+ let box _x = Box::new('c');
+}

tests/ui/feature-gates/feature-gate-deref_patterns.stderr

@@ -0,0 +1,13 @@
+error[E0658]: box pattern syntax is experimental
+ --> $DIR/feature-gate-deref_patterns.rs:3:9
+ |
+LL | let box x = Box::new('c');
+ | ^^^^^
+ |
+ = note: see issue #29641 <https://github.com/rust-lang/rust/issues/29641> for more information
+ = help: add `#![feature(box_patterns)]` to the crate attributes to enable
+ = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0658`.

tests/ui/pattern/deref-patterns/typeck.rs

@@ -0,0 +1,31 @@
+//@ check-pass
+#![feature(deref_patterns)]
+#![allow(incomplete_features)]
+
+use std::rc::Rc;
+
+fn main() {
+ let vec: Vec<u32> = Vec::new();
+ match vec {
+ box [..] => {}
+ _ => {}
+ }
+ match Box::new(true) {
+ box true => {}
+ _ => {}
+ }
+ match &Box::new(true) {
+ box true => {}
+ _ => {}
+ }
+ match &Rc::new(0) {
+ box (1..) => {}
+ _ => {}
+ }
+ // FIXME(deref_patterns): fails to typecheck because `"foo"` has type &str but deref creates a
+ // place of type `str`.
+ // match "foo".to_string() {
+ // box "foo" => {}
+ // _ => {}
+ // }
+}