[clang] [clang][AST] Pretty-print default template template args (PR #162134)

[Andrey Ali Khan Bolshakov via cfe-commits]

https://github.com/bolshakov-a updated https://github.com/llvm/llvm-project/pull/162134

>From 6afe3fe6f81f920d5ea6019b1117f42f8c079195 Mon Sep 17 00:00:00 2001
From: Bolshakov <bolsh.andrey at yandex.ru>
Date: Mon, 6 Oct 2025 21:57:33 +0300
Subject: [PATCH] [clang][AST] Pretty-print default template template args

---
 clang/docs/ReleaseNotes.rst             | 2 +-
 clang/lib/AST/DeclPrinter.cpp           | 6 +++++-
 clang/test/AST/ast-print-record-decl.c  | 7 +++++++
 clang/unittests/AST/DeclPrinterTest.cpp | 2 +-
 4 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 390e0fa7a9a2b..be585e4919b54 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -124,7 +124,7 @@ AST Dumping Potentially Breaking Changes
     ``__atomic_test_and_set(p, 0)``
 
 - Pretty-printing of templates with inherited (i.e. specified in a previous
-  redeclaration) default arguments has been fixed.
+  redeclaration) and template default arguments has been fixed.
 
 Clang Frontend Potentially Breaking Changes
 -------------------------------------------
diff --git a/clang/lib/AST/DeclPrinter.cpp b/clang/lib/AST/DeclPrinter.cpp
index 7001adeff5397..b2a837b82bb13 100644
--- a/clang/lib/AST/DeclPrinter.cpp
+++ b/clang/lib/AST/DeclPrinter.cpp
@@ -1190,7 +1190,11 @@ void DeclPrinter::printTemplateParameters(const TemplateParameterList *Params,
       VisitNonTypeTemplateParmDecl(NTTP);
     } else if (auto TTPD = dyn_cast<TemplateTemplateParmDecl>(Param)) {
       VisitTemplateDecl(TTPD);
-      // FIXME: print the default argument, if present.
+      if (TTPD->hasDefaultArgument() && !TTPD->defaultArgumentWasInherited()) {
+        Out << " = ";
+        TTPD->getDefaultArgument().getArgument().print(Policy, Out,
+                                                       /*IncludeType=*/false);
+      }
     }
   }
 
diff --git a/clang/test/AST/ast-print-record-decl.c b/clang/test/AST/ast-print-record-decl.c
index fd815881ebeb0..394f837c3645d 100644
--- a/clang/test/AST/ast-print-record-decl.c
+++ b/clang/test/AST/ast-print-record-decl.c
@@ -315,4 +315,11 @@ template <int, int = 0> KW SmearedNTTPDefArgs;
 // PRINT-CXX-NEXT: template <int = 0, int> [[KW]] SmearedNTTPDefArgs;
 template <int = 0, int> KW SmearedNTTPDefArgs;
 
+// PRINT-CXX-LABEL: Tpl
+template <int> KW Tpl;
+// PRINT-CXX-NEXT: template <template <int> class, template <int> class = Tpl> [[KW]] SmearedTplDefArgs;
+template <template <int> class, template <int> class = Tpl> KW SmearedTplDefArgs;
+// PRINT-CXX-NEXT: template <template <int> class = Tpl, template <int> class> [[KW]] SmearedTplDefArgs;
+template <template <int> class = Tpl, template <int> class> KW SmearedTplDefArgs;
+
 #endif
diff --git a/clang/unittests/AST/DeclPrinterTest.cpp b/clang/unittests/AST/DeclPrinterTest.cpp
index 1a1b707c8dd37..a412a9813b470 100644
--- a/clang/unittests/AST/DeclPrinterTest.cpp
+++ b/clang/unittests/AST/DeclPrinterTest.cpp
@@ -1090,7 +1090,7 @@ TEST(DeclPrinter, TestClassTemplateDecl9) {
       "template<typename T> struct Z { };"
       "template<template<typename U> class T = Z> struct A { };",
       classTemplateDecl(hasName("A")).bind("id"),
-      "template <template <typename U> class T> struct A {}"));
+      "template <template <typename U> class T = Z> struct A {}"));
 }
 
 TEST(DeclPrinter, TestClassTemplateDecl10) {