[clang][AST] Pretty-print default template template args

clang/docs/ReleaseNotes.rst

@@ -126,6 +126,8 @@ AST Dumping Potentially Breaking Changes
 - Pretty-printing of templates with inherited (i.e. specified in a previous
   redeclaration) default arguments has been fixed.
 
+- Default arguments of template template parameters are pretty-printed now.
+
 Clang Frontend Potentially Breaking Changes
 -------------------------------------------
 - Members of anonymous unions/structs are now injected as ``IndirectFieldDecl``

clang/lib/AST/DeclPrinter.cpp

@@ -111,6 +111,7 @@ namespace {
     void VisitOMPCapturedExprDecl(OMPCapturedExprDecl *D);
     void VisitTemplateTypeParmDecl(const TemplateTypeParmDecl *TTP);
     void VisitNonTypeTemplateParmDecl(const NonTypeTemplateParmDecl *NTTP);
+    void VisitTemplateTemplateParmDecl(const TemplateTemplateParmDecl *);
     void VisitHLSLBufferDecl(HLSLBufferDecl *D);
 
     void VisitOpenACCDeclareDecl(OpenACCDeclareDecl *D);
@@ -1189,8 +1190,7 @@ void DeclPrinter::printTemplateParameters(const TemplateParameterList *Params,
     } else if (auto NTTP = dyn_cast<NonTypeTemplateParmDecl>(Param)) {
       VisitNonTypeTemplateParmDecl(NTTP);
     } else if (auto TTPD = dyn_cast<TemplateTemplateParmDecl>(Param)) {
-      VisitTemplateDecl(TTPD);
-      // FIXME: print the default argument, if present.
+      VisitTemplateTemplateParmDecl(TTPD);
     }
   }
 
@@ -1916,6 +1916,16 @@ void DeclPrinter::VisitNonTypeTemplateParmDecl(
   }
 }
 
+void DeclPrinter::VisitTemplateTemplateParmDecl(
+    const TemplateTemplateParmDecl *TTPD) {
+  VisitTemplateDecl(TTPD);
+  if (TTPD->hasDefaultArgument() && !TTPD->defaultArgumentWasInherited()) {
+    Out << " = ";
+    TTPD->getDefaultArgument().getArgument().print(Policy, Out,
+                                                   /*IncludeType=*/false);
+  }
+}
+
 void DeclPrinter::VisitOpenACCDeclareDecl(OpenACCDeclareDecl *D) {
   if (!D->isInvalidDecl()) {
     Out << "#pragma acc declare";

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

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) {