From a6b3751b19a4ab257bcfd87e1ba03f396186a454 Mon Sep 17 00:00:00 2001
From: Iain Buclaw <ibuclaw@gdcproject.org>
Date: Sun, 6 Apr 2025 01:31:30 +0200
Subject: [PATCH] fix #21153 - [REG 2.111.0] Infinite loop in isAliasThisTuple
 (#21154)

---
 compiler/src/dmd/expressionsem.d     | 4 ++++
 compiler/test/compilable/test21153.d | 8 ++++++++
 2 files changed, 12 insertions(+)
 create mode 100644 compiler/test/compilable/test21153.d

diff --git a/compiler/src/dmd/expressionsem.d b/compiler/src/dmd/expressionsem.d
index b0278cbaca..7d47f5bc56 100644
--- a/compiler/src/dmd/expressionsem.d
+++ b/compiler/src/dmd/expressionsem.d
@@ -655,7 +655,11 @@ TupleDeclaration isAliasThisTuple(Expression e)
                 return td;
         }
         if (Type att = t.aliasthisOf())
+        {
             t = att;
+            continue;
+        }
+        return null;
     }
 }
 
diff --git a/compiler/test/compilable/test21153.d b/compiler/test/compilable/test21153.d
new file mode 100644
index 0000000000..cd92a31240
--- /dev/null
+++ b/compiler/test/compilable/test21153.d
@@ -0,0 +1,8 @@
+// https://github.com/dlang/dmd/issues/21153
+alias AliasSeq(TList...) = TList;
+class DataClass;
+void reduce(DataClass[] r)
+{
+    alias Args = AliasSeq!(DataClass);
+    Args result = r[0];
+}