Rollup merge of #104669 - LeSeulArtichaut:88015-if-let-guard-bindings, r=cjgillot

Only declare bindings for if-let guards once per arm

Currently, each candidate for a match arm uses separate locals for the bindings in the if-let guard, causing problems (#88015) when those branches converge in the arm body.

Fixes #88015 (🤞)

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 @@ fn ast_block_stmts(
                                         visibility_scope,
                                         remainder_span,
                                         pattern,
-                                        ArmHasGuard(false),
+                                        None,
                                         Some((None, initializer_span)),
                                     );
                                     this.visit_primary_bindings(
@@ -308,7 +307,7 @@ fn ast_block_stmts(
                                             visibility_scope,
                                             remainder_span,
                                             pattern,
-                                            ArmHasGuard(false),
+                                            None,
                                             Some((None, initializer_span)),
                                         );
                                         this.expr_into_pattern(block, &pattern, init)
@@ -324,7 +323,7 @@ fn ast_block_stmts(
                                 visibility_scope,
                                 remainder_span,
                                 pattern,
-                                ArmHasGuard(false),
+                                None,
                                 None,
                             );
                             block.unit()

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

@@ -108,7 +108,7 @@ pub(crate) fn expr_into_dest(
             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 @@ pub(crate) fn then_else_break(
                 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 @@ fn lower_match_arms(
                         None,
                         arm.span,
                         &arm.pattern,
-                        ArmHasGuard(arm.guard.is_some()),
+                        arm.guard.as_ref(),
                         opt_scrutinee_place,
                     );
 
@@ -645,7 +646,7 @@ pub(crate) fn declare_bindings(
         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 @@ pub(crate) fn declare_bindings(
                     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 @@ fn calculate_fake_borrows<'b>(
 // 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 @@ pub(crate) fn lower_let_expr(
         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 @@ pub(crate) fn lower_let_expr(
         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 @@ fn bind_and_guard_matched_candidate<'pat>(
                     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 @@ fn args_and_body(
                         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!()
+    }
 }