From 651d01e873c6fce3c8d300362585b1a5f98bb883 Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234@gmail.com>
Date: Tue, 8 Sep 2026 08:47:13 -0400
Subject: [PATCH] [clang][AST] Fix infinite recursion when printing fully
 qualified template parameters (#219044)

This fixes an infinite recursion crash that was introduced in #206041.

When printing a `DeclRefExpr` using
`PrintingPolicy::FullyQualifiedName`, we were previously trying to print
the fully qualified name of all decls. However, when the decl is a
template parameter, its `DeclContext` is the template specialization
itself. If a template specialization's arguments depend on that same
template parameter (e.g., `template<int Count> struct
View<int[Count]>`), attempting to print the qualified name forces Clang
to recursively evaluate the enclosing context. This led to unbounded
recursion (`View<int[Count]>::Count` ->
`View<int[View<int[Count]>::Count]>::Count` and so on). Since template
parameters are inherently scoped to their template declarations and do
not require a fully qualified name, this patch resolves the issue by
skipping `printQualifiedName` if the decl is a template parameter
(`!VD->isTemplateParameter()`).

Fixes #218076.
---
 clang/lib/AST/StmtPrinter.cpp           |  3 ++-
 clang/unittests/AST/TypePrinterTest.cpp | 18 ++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/clang/lib/AST/StmtPrinter.cpp b/clang/lib/AST/StmtPrinter.cpp
index 77a3fcfd3ad08..a3da70962f4f5 100644
--- a/clang/lib/AST/StmtPrinter.cpp
+++ b/clang/lib/AST/StmtPrinter.cpp
@@ -1378,7 +1378,8 @@ void StmtPrinter::VisitDeclRefExpr(DeclRefExpr *Node) {
   bool CleanUglifiedParameter = Policy.CleanUglifiedParameters &&
                                 isa<ParmVarDecl, NonTypeTemplateParmDecl>(VD);
 
-  if (Policy.FullyQualifiedName && !ForceAnonymous && !CleanUglifiedParameter) {
+  if (Policy.FullyQualifiedName && !ForceAnonymous && !CleanUglifiedParameter &&
+      !VD->isTemplateParameter()) {
     VD->printQualifiedName(OS, Policy);
   } else {
     Node->getQualifier().print(OS, Policy);
diff --git a/clang/unittests/AST/TypePrinterTest.cpp b/clang/unittests/AST/TypePrinterTest.cpp
index 79f75909c57b5..8a319faabdb96 100644
--- a/clang/unittests/AST/TypePrinterTest.cpp
+++ b/clang/unittests/AST/TypePrinterTest.cpp
@@ -145,6 +145,24 @@ TEST(TypePrinter, TemplateArgumentExpressionFullyQualified) {
       [](PrintingPolicy &Policy) { Policy.FullyQualifiedName = true; }));
 }
 
+TEST(TypePrinter, TemplateSpecializationWithDependentSizedArrayType) {
+  llvm::StringLiteral Code = R"cpp(
+    template<typename Container>
+    struct View {};
+
+    template<int Count>
+    struct View<int[Count]> {
+      using Container = int[Count];
+    };
+  )cpp";
+
+  auto Matcher =
+      typeAliasDecl(hasName("Container"), hasType(qualType().bind("id")));
+  ASSERT_TRUE(PrintedTypeMatches(
+      Code, {}, Matcher, "int[Count]",
+      [](PrintingPolicy &Policy) { Policy.FullyQualifiedName = true; }));
+}
+
 TEST(TypePrinter, TemplateIdWithNTTP) {
   constexpr char Code[] = R"cpp(
     template <int N>