[clang-tidy] modernize-use-using: Fix broken fixit with InjectedClassName

Summary:
Before this PR, `modernize-use-using` would transform the typedef in
```
template <int A>
struct InjectedClassName {
  typedef InjectedClassName b;
};
```
into `using b = InjectedClassName<A>;` and
```
template <int>
struct InjectedClassNameWithUnnamedArgument {
  typedef InjectedClassNameWithUnnamedArgument b;
};
```
into `using b = InjectedClassNameWithUnnamedArgument<>;`.
The first fixit is surprising because its different than the code
before, but the second fixit doesn't even compile.

This PR adds an option to the TypePrinter to print InjectedClassNameType without
template parameters (i.e. as written).

Reviewers: aaron.ballman, alexfh, hokein, njames93

Subscribers: xazax.hun, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77979

Author: mgehre

clang-tools-extra/clang-tidy/modernize/UseUsingCheck.cpp

@@ -58,6 +58,7 @@ void UseUsingCheck::check(const MatchFinder::MatchResult &Result) {
   printPolicy.SuppressScope = true;
   printPolicy.ConstantArraySizeAsWritten = true;
   printPolicy.UseVoidForZeroParams = false;
+  printPolicy.PrintInjectedClassNameWithArguments = false;
 
   std::string Type = MatchedDecl->getUnderlyingType().getAsString(printPolicy);
   std::string Name = MatchedDecl->getNameAsString();

clang-tools-extra/test/clang-tidy/checkers/modernize-use-using.cpp

@@ -289,3 +289,16 @@ typedef enum { ea2, eb2 } EnumT2_CheckTypedefImpactFromAnotherFile;
 // CHECK-MESSAGES: :[[@LINE-1]]:1: warning: use 'using' instead of 'typedef'
 // CHECK-FIXES: using EnumT2_CheckTypedefImpactFromAnotherFile = enum { ea2, eb2 };
 
+template <int A>
+struct InjectedClassName {
+  typedef InjectedClassName b;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: use 'using' instead of 'typedef'
+  // CHECK-FIXES: using b = InjectedClassName;
+};
+
+template <int>
+struct InjectedClassNameWithUnnamedArgument {
+  typedef InjectedClassNameWithUnnamedArgument b;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: use 'using' instead of 'typedef'
+  // CHECK-FIXES: using b = InjectedClassNameWithUnnamedArgument;
+};

clang/include/clang/AST/PrettyPrinter.h

@@ -63,7 +63,7 @@ struct PrintingPolicy {
         MSWChar(LO.MicrosoftExt && !LO.WChar), IncludeNewlines(true),
         MSVCFormatting(false), ConstantsAsWritten(false),
         SuppressImplicitBase(false), FullyQualifiedName(false),
-        PrintCanonicalTypes(false) {}
+        PrintCanonicalTypes(false), PrintInjectedClassNameWithArguments(true) {}
 
   /// Adjust this printing policy for cases where it's known that we're
   /// printing C++ code (for instance, if AST dumping reaches a C++-only
@@ -244,6 +244,11 @@ struct PrintingPolicy {
   /// Whether to print types as written or canonically.
   unsigned PrintCanonicalTypes : 1;
 
+  /// Whether to print an InjectedClassNameType with template arguments or as
+  /// written. When a template argument is unnamed, printing it results in
+  /// invalid C++ code.
+  unsigned PrintInjectedClassNameWithArguments : 1;
+
   /// Callbacks to use to allow the behavior of printing to be customized.
   const PrintingCallbacks *Callbacks = nullptr;
 };

clang/lib/AST/TypePrinter.cpp

@@ -1329,7 +1329,12 @@ void TypePrinter::printTemplateSpecializationAfter(
 
 void TypePrinter::printInjectedClassNameBefore(const InjectedClassNameType *T,
                                                raw_ostream &OS) {
-  printTemplateSpecializationBefore(T->getInjectedTST(), OS);
+  if (Policy.PrintInjectedClassNameWithArguments)
+    return printTemplateSpecializationBefore(T->getInjectedTST(), OS);
+
+  IncludeStrongLifetimeRAII Strong(Policy);
+  T->getTemplateName().print(OS, Policy);
+  spaceBeforePlaceHolder(OS);
 }
 
 void TypePrinter::printInjectedClassNameAfter(const InjectedClassNameType *T,