Introduce if-let guards in the HIR

1 files changed, 10 insertions, 5 deletions

diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index e0e78a4d609..7c95c7f6480 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -505,14 +505,19 @@ 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(ref pat, ref scrutinee) = cond.kind {
+                hir::Guard::IfLet(self.lower_pat(pat), self.lower_expr(scrutinee))
+            } else {
+                hir::Guard::If(self.lower_expr(cond))
+            }
+        });
         hir::Arm {
             hir_id: self.next_id(),
             attrs: self.lower_attrs(&arm.attrs),
-            pat: self.lower_pat(&arm.pat),
-            guard: match arm.guard {
-                Some(ref x) => Some(hir::Guard::If(self.lower_expr(x))),
-                _ => None,
-            },
+            pat,
+            guard,
             body: self.lower_expr(&arm.body),
             span: arm.span,
         }