From 5c0e25237c62675f7118a4a8a60985fca9afc4e4 Mon Sep 17 00:00:00 2001
From: Lukas Wirth <lukastw97@gmail.com>
Date: Wed, 31 Aug 2022 10:04:01 +0200
Subject: [PATCH] Drop the expander borrow in all control flow paths

The change in https://github.com/rust-lang/rust-analyzer/pull/13123
actually re-uses the RefMut borrow instead of dropping it so we need to
drop it manually where required.
---
 crates/hir-ty/src/lower.rs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/crates/hir-ty/src/lower.rs b/crates/hir-ty/src/lower.rs
index 3f6d0844e9c..708e63d7fd3 100644
--- a/crates/hir-ty/src/lower.rs
+++ b/crates/hir-ty/src/lower.rs
@@ -332,7 +332,10 @@ impl<'a> TyLoweringContext<'a> {
             TypeRef::Macro(macro_call) => {
                 let (mut expander, recursion_start) = {
                     match RefMut::filter_map(self.expander.borrow_mut(), Option::as_mut) {
+                        // There already is an expander here, this means we are already recursing
                         Ok(expander) => (expander, false),
+                        // No expander was created yet, so we are at the start of the expansion recursion
+                        // and therefore have to create an expander.
                         Err(expander) => (
                             RefMut::map(expander, |it| {
                                 it.insert(Expander::new(
@@ -362,9 +365,14 @@ impl<'a> TyLoweringContext<'a> {
                                 .exit(self.db.upcast(), mark);
                             Some(ty)
                         }
-                        _ => None,
+                        _ => {
+                            drop(expander);
+                            None
+                        }
                     }
                 };
+
+                // drop the expander, resetting it to pre-recursion state
                 if recursion_start {
                     *self.expander.borrow_mut() = None;
                 }