From b7e884bbf0cbf7cc3064959d9a11132f6cd03008 Mon Sep 17 00:00:00 2001
From: Hiroshi Yamauchi <hjyamauchi@gmail.com>
Date: Tue, 24 Oct 2023 09:27:27 -0700
Subject: [PATCH] Fix a round trip debug type failure with typealias

When checking equality of types with existential types removed,
recursively remove existential types inside an existential type.

Fixes: #66554

Cherrypick https://github.com/apple/swift/commit/fda6f9b62febaba0620469a901de4168df47e27e
---
 lib/IRGen/IRGenDebugInfo.cpp                      |  7 ++++---
 test/IRGen/round-trip-debug-types-typealias.swift | 10 ++++++++++
 2 files changed, 14 insertions(+), 3 deletions(-)
 create mode 100644 test/IRGen/round-trip-debug-types-typealias.swift

diff --git a/lib/IRGen/IRGenDebugInfo.cpp b/lib/IRGen/IRGenDebugInfo.cpp
index 1b01a83d9991d..32829b1e6d7e7 100644
--- a/lib/IRGen/IRGenDebugInfo.cpp
+++ b/lib/IRGen/IRGenDebugInfo.cpp
@@ -98,10 +98,11 @@ class EqualUpToClangTypes
 };
 
 static bool equalWithoutExistentialTypes(Type t1, Type t2) {
-  auto withoutExistentialTypes = [](Type type) -> Type {
+  static Type (*withoutExistentialTypes)(Type) = [](Type type) -> Type {
     return type.transform([](Type type) -> Type {
-      if (auto existential = type->getAs<ExistentialType>())
-        return existential->getConstraintType();
+      if (auto existential = type->getAs<ExistentialType>()) {
+        return withoutExistentialTypes(existential->getConstraintType());
+      }
       return type;
     });
   };
diff --git a/test/IRGen/round-trip-debug-types-typealias.swift b/test/IRGen/round-trip-debug-types-typealias.swift
new file mode 100644
index 0000000000000..722124ae9bfcf
--- /dev/null
+++ b/test/IRGen/round-trip-debug-types-typealias.swift
@@ -0,0 +1,10 @@
+// RUN: %target-build-swift -g %s
+
+// https://github.com/apple/swift/issues/66554
+// IRGenDebugInfo type reconstruction crash because existential types
+// inside typealias are not taken into account when comparing type
+// equality
+
+protocol Protocol<T> { associatedtype T }
+typealias AnyProtocol<T> = any Protocol<T>
+let crash: AnyProtocol<Any?>