Only declare bindings for if-let guards once per arm

Author: LeSeulArtichaut

compiler/rustc_mir_build/src/build/block.rs

@@ -1,4 +1,3 @@
-use crate::build::matches::ArmHasGuard;
 use crate::build::ForGuard::OutsideGuard;
 use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
 use rustc_middle::middle::region::Scope;
@@ -231,7 +230,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  visibility_scope,
  remainder_span,
  pattern,
- ArmHasGuard(false),
+ None,
  Some((None, initializer_span)),
  );
  this.visit_primary_bindings(
@@ -308,7 +307,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  visibility_scope,
  remainder_span,
  pattern,
- ArmHasGuard(false),
+ None,
  Some((None, initializer_span)),
  );
  this.expr_into_pattern(block, &pattern, init)
@@ -324,7 +323,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  visibility_scope,
  remainder_span,
  pattern,
- ArmHasGuard(false),
+ None,
  None,
  );
  block.unit()

compiler/rustc_mir_build/src/build/expr/into.rs

@@ -108,7 +108,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  ExprKind::Let { expr, ref pat } => {
  let scope = this.local_scope();
  let (true_block, false_block) = this.in_if_then_scope(scope, expr_span, |this| {
- this.lower_let_expr(block, &this.thir[expr], pat, scope, None, expr_span)
+ this.lower_let_expr(block, &this.thir[expr], pat, scope, None, expr_span, true)
  });
 
  this.cfg.push_assign_constant(

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

@@ -84,6 +84,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  break_scope,
  Some(variable_source_info.scope),
  variable_source_info.span,
+ true,
  ),
  _ => {
  let temp_scope = temp_scope_override.unwrap_or_else(|| this.local_scope());
@@ -357,7 +358,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  None,
  arm.span,
  &arm.pattern,
- ArmHasGuard(arm.guard.is_some()),
+ arm.guard.as_ref(),
  opt_scrutinee_place,
  );
 
@@ -645,7 +646,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  mut visibility_scope: Option<SourceScope>,
  scope_span: Span,
  pattern: &Pat<'tcx>,
- has_guard: ArmHasGuard,
+ guard: Option<&Guard<'tcx>>,
  opt_match_place: Option<(Option<&Place<'tcx>>, Span)>,
  ) -> Option<SourceScope> {
  self.visit_primary_bindings(
@@ -667,12 +668,16 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  var,
  ty,
  user_ty,
- has_guard,
+ ArmHasGuard(guard.is_some()),
  opt_match_place.map(|(x, y)| (x.cloned(), y)),
  pattern.span,
  );
  },
  );
+ if let Some(Guard::IfLet(guard_pat, _)) = guard {
+ // FIXME: pass a proper `opt_match_place`
+ self.declare_bindings(visibility_scope, scope_span, guard_pat, None, None);
+ }
  visibility_scope
  }
 
@@ -1766,6 +1771,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 // Pat binding - used for `let` and function parameters as well.
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
+ /// If the bindings have already been declared, set `declare_bindings` to
+ /// `false` to avoid duplicated bindings declaration. Used for if-let guards.
  pub(crate) fn lower_let_expr(
  &mut self,
  mut block: BasicBlock,
@@ -1774,6 +1781,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  else_target: region::Scope,
  source_scope: Option<SourceScope>,
  span: Span,
+ declare_bindings: bool,
  ) -> BlockAnd<()> {
  let expr_span = expr.span;
  let expr_place_builder = unpack!(block = self.lower_scrutinee(block, expr, expr_span));
@@ -1797,13 +1805,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  let otherwise_post_guard_block = otherwise_candidate.pre_binding_block.unwrap();
  self.break_for_else(otherwise_post_guard_block, else_target, self.source_info(expr_span));
 
- self.declare_bindings(
- source_scope,
- pat.span.to(span),
- pat,
- ArmHasGuard(false),
- opt_expr_place,
- );
+ if declare_bindings {
+ self.declare_bindings(source_scope, pat.span.to(span), pat, None, opt_expr_place);
+ }
 
  let post_guard_block = self.bind_pattern(
  self.source_info(pat.span),
@@ -1984,7 +1988,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  Guard::IfLet(ref pat, scrutinee) => {
  let s = &this.thir[scrutinee];
  guard_span = s.span;
- this.lower_let_expr(block, s, pat, match_scope, None, arm.span)
+ this.lower_let_expr(block, s, pat, match_scope, None, arm.span, false)
  }
  });
 

compiler/rustc_mir_build/src/build/mod.rs

@@ -924,7 +924,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  scope,
  expr.span,
  &pat,
- matches::ArmHasGuard(false),
+ None,
  Some((Some(&place), span)),
  );
  let place_builder = PlaceBuilder::from(local);

src/test/ui/rfc-2294-if-let-guard/run-pass.rs

@@ -30,4 +30,11 @@ fn main() {
  Some(x) if let Foo::Qux(y) = qux(x) => assert_eq!(y, 84),
  _ => panic!(),
  }
+
+ // issue #88015
+ #[allow(irrefutable_let_patterns)]
+ match () {
+ () | () if let x = 42 => assert_eq!(x, 42),
+ _ => panic!()
+ }
 }