Rollup merge of rust-lang#119554 - matthewjasper:remove-guard-distinction, r=compiler-errors

Fix scoping for let chains in match guards

If let guards were previously represented as a different type of guard in HIR and THIR. This meant that let chains in match guards were not handled correctly because they were treated exactly like normal guards.

- Remove `hir::Guard` and `thir::Guard`.
- Make the scoping different between normal guards and if let guards also check for let chains.

closes rust-lang#118593

Author: matthiaskrgr

compiler/rustc_ast_lowering/src/expr.rs

@@ -546,20 +546,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     fn lower_arm(&mut self, arm: &Arm) -> hir::Arm<'hir> {
         let pat = self.lower_pat(&arm.pat);
-        let guard = arm.guard.as_ref().map(|cond| {
-            if let ExprKind::Let(pat, scrutinee, span, is_recovered) = &cond.kind {
-                hir::Guard::IfLet(self.arena.alloc(hir::Let {
-                    hir_id: self.next_id(),
-                    span: self.lower_span(*span),
-                    pat: self.lower_pat(pat),
-                    ty: None,
-                    init: self.lower_expr(scrutinee),
-                    is_recovered: *is_recovered,
-                }))
-            } else {
-                hir::Guard::If(self.lower_expr(cond))
-            }
-        });
+        let guard = arm.guard.as_ref().map(|cond| self.lower_expr(cond));
         let hir_id = self.next_id();
         let span = self.lower_span(arm.span);
         self.lower_attrs(hir_id, &arm.attrs);

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -3590,7 +3590,7 @@ impl<'b, 'v> Visitor<'v> for ConditionVisitor<'b> {
                                 ));
                             } else if let Some(guard) = &arm.guard {
                                 self.errors.push((
-                                    arm.pat.span.to(guard.body().span),
+                                    arm.pat.span.to(guard.span),
                                     format!(
                                         "if this pattern and condition are matched, {} is not \
                                          initialized",

compiler/rustc_hir/src/hir.rs

@@ -1258,7 +1258,7 @@ pub struct Arm<'hir> {
     /// If this pattern and the optional guard matches, then `body` is evaluated.
     pub pat: &'hir Pat<'hir>,
     /// Optional guard clause.
-    pub guard: Option<Guard<'hir>>,
+    pub guard: Option<&'hir Expr<'hir>>,
     /// The expression the arm evaluates to if this arm matches.
     pub body: &'hir Expr<'hir>,
 }
@@ -1280,26 +1280,6 @@ pub struct Let<'hir> {
     pub is_recovered: Option<ErrorGuaranteed>,
 }
 
-#[derive(Debug, Clone, Copy, HashStable_Generic)]
-pub enum Guard<'hir> {
-    If(&'hir Expr<'hir>),
-    IfLet(&'hir Let<'hir>),
-}
-
-impl<'hir> Guard<'hir> {
-    /// Returns the body of the guard
-    ///
-    /// In other words, returns the e in either of the following:
-    ///
-    /// - `if e`
-    /// - `if let x = e`
-    pub fn body(&self) -> &'hir Expr<'hir> {
-        match self {
-            Guard::If(e) | Guard::IfLet(Let { init: e, .. }) => e,
-        }
-    }
-}
-
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub struct ExprField<'hir> {
     #[stable_hasher(ignore)]

compiler/rustc_hir/src/intravisit.rs

@@ -619,13 +619,8 @@ pub fn walk_stmt<'v, V: Visitor<'v>>(visitor: &mut V, statement: &'v Stmt<'v>) {
 pub fn walk_arm<'v, V: Visitor<'v>>(visitor: &mut V, arm: &'v Arm<'v>) {
     visitor.visit_id(arm.hir_id);
     visitor.visit_pat(arm.pat);
-    if let Some(ref g) = arm.guard {
-        match g {
-            Guard::If(ref e) => visitor.visit_expr(e),
-            Guard::IfLet(ref l) => {
-                visitor.visit_let_expr(l);
-            }
-        }
+    if let Some(ref e) = arm.guard {
+        visitor.visit_expr(e);
     }
     visitor.visit_expr(arm.body);
 }

compiler/rustc_hir_analysis/src/check/region.rs

@@ -177,14 +177,24 @@ fn resolve_block<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, blk: &'tcx h
 }
 
 fn resolve_arm<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, arm: &'tcx hir::Arm<'tcx>) {
+    fn has_let_expr(expr: &Expr<'_>) -> bool {
+        match &expr.kind {
+            hir::ExprKind::Binary(_, lhs, rhs) => has_let_expr(lhs) || has_let_expr(rhs),
+            hir::ExprKind::Let(..) => true,
+            _ => false,
+        }
+    }
+
     let prev_cx = visitor.cx;
 
     visitor.terminating_scopes.insert(arm.hir_id.local_id);
 
     visitor.enter_node_scope_with_dtor(arm.hir_id.local_id);
     visitor.cx.var_parent = visitor.cx.parent;
 
-    if let Some(hir::Guard::If(expr)) = arm.guard {
+    if let Some(expr) = arm.guard
+        && !has_let_expr(expr)
+    {
         visitor.terminating_scopes.insert(expr.hir_id.local_id);
     }
 

compiler/rustc_hir_pretty/src/lib.rs

@@ -1874,17 +1874,9 @@ impl<'a> State<'a> {
         self.print_pat(arm.pat);
         self.space();
         if let Some(ref g) = arm.guard {
-            match *g {
-                hir::Guard::If(e) => {
-                    self.word_space("if");
-                    self.print_expr(e);
-                    self.space();
-                }
-                hir::Guard::IfLet(&hir::Let { pat, ty, init, .. }) => {
-                    self.word_nbsp("if");
-                    self.print_let(pat, ty, init);
-                }
-            }
+            self.word_space("if");
+            self.print_expr(g);
+            self.space();
         }
         self.word_space("=>");
 

compiler/rustc_hir_typeck/src/_match.rs

@@ -78,16 +78,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let mut other_arms = vec![]; // Used only for diagnostics.
         let mut prior_arm = None;
         for arm in arms {
-            if let Some(g) = &arm.guard {
+            if let Some(e) = &arm.guard {
                 self.diverges.set(Diverges::Maybe);
-                match g {
-                    hir::Guard::If(e) => {
-                        self.check_expr_has_type_or_error(e, tcx.types.bool, |_| {});
-                    }
-                    hir::Guard::IfLet(l) => {
-                        self.check_expr_let(l);
-                    }
-                };
+                self.check_expr_has_type_or_error(e, tcx.types.bool, |_| {});
             }
 
             self.diverges.set(Diverges::Maybe);

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -669,12 +669,8 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
         );
         self.walk_pat(discr_place, arm.pat, arm.guard.is_some());
 
-        match arm.guard {
-            Some(hir::Guard::If(e)) => self.consume_expr(e),
-            Some(hir::Guard::IfLet(l)) => {
-                self.walk_local(l.init, l.pat, None, |t| t.borrow_expr(l.init, ty::ImmBorrow))
-            }
-            None => {}
+        if let Some(ref e) = arm.guard {
+            self.consume_expr(e)
         }
 
         self.consume_expr(arm.body);

compiler/rustc_middle/src/thir.rs

@@ -519,20 +519,13 @@ pub struct FruInfo<'tcx> {
 #[derive(Clone, Debug, HashStable)]
 pub struct Arm<'tcx> {
     pub pattern: Box<Pat<'tcx>>,
-    pub guard: Option<Guard<'tcx>>,
+    pub guard: Option<ExprId>,
     pub body: ExprId,
     pub lint_level: LintLevel,
     pub scope: region::Scope,
     pub span: Span,
 }
 
-/// A `match` guard.
-#[derive(Clone, Debug, HashStable)]
-pub enum Guard<'tcx> {
-    If(ExprId),
-    IfLet(Box<Pat<'tcx>>, ExprId),
-}
-
 #[derive(Copy, Clone, Debug, HashStable)]
 pub enum LogicalOp {
     /// The `&&` operator.

compiler/rustc_middle/src/thir/visit.rs

@@ -1,5 +1,5 @@
 use super::{
-    AdtExpr, Arm, Block, ClosureExpr, Expr, ExprKind, Guard, InlineAsmExpr, InlineAsmOperand, Pat,
+    AdtExpr, Arm, Block, ClosureExpr, Expr, ExprKind, InlineAsmExpr, InlineAsmOperand, Pat,
     PatKind, Stmt, StmtKind, Thir,
 };
 
@@ -213,13 +213,8 @@ pub fn walk_arm<'thir, 'tcx: 'thir, V: Visitor<'thir, 'tcx>>(
     visitor: &mut V,
     arm: &'thir Arm<'tcx>,
 ) {
-    match arm.guard {
-        Some(Guard::If(expr)) => visitor.visit_expr(&visitor.thir()[expr]),
-        Some(Guard::IfLet(ref pat, expr)) => {
-            visitor.visit_pat(pat);
-            visitor.visit_expr(&visitor.thir()[expr]);
-        }
-        None => {}
+    if let Some(expr) = arm.guard {
+        visitor.visit_expr(&visitor.thir()[expr])
     }
     visitor.visit_pat(&arm.pattern);
     visitor.visit_expr(&visitor.thir()[arm.body]);