[clang-tidy] Address false positive in modernize-use-default-member-init

[njames93]

Summary

Fixes incorrect warning emitted by "modernize-use-default-member-init" (new to 10.0.0).

[aaron.ballman]

LGTM with a testing request.

clang-tools-extra/test/clang-tidy/checkers/modernize-use-default-member-init.cpp

436

Can you add a test where the value is elided but braced init is still used:

struct PR45363 {
  PR45363() : m_i{} {} // This should still warn
  int m_i;
};

[njames93]

• Added test case

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

 #include "clang/Lex/Lexer.h"
 
 using namespace clang::ast_matchers;
 
 namespace clang {
 namespace tidy {
 namespace modernize {
 
+namespace {
+AST_MATCHER_P(InitListExpr, initCountIs, unsigned, N) {
+  return Node.getNumInits() == N;
+}
+} // namespace
+
 static StringRef getValueOfValueInit(const QualType InitType) {
   switch (InitType->getScalarTypeKind()) {
   case Type::STK_CPointer:
   case Type::STK_BlockPointer:
   case Type::STK_ObjCObjectPointer:
   case Type::STK_MemberPointer:
     return "nullptr";
 

 
 void UseDefaultMemberInitCheck::storeOptions(
     ClangTidyOptions::OptionMap &Opts) {
   Options.store(Opts, "UseAssignment", UseAssignment);
   Options.store(Opts, "IgnoreMacros", IgnoreMacros);
 }
 
 void UseDefaultMemberInitCheck::registerMatchers(MatchFinder *Finder) {
-  auto Init =
+  auto InitBase =
       anyOf(stringLiteral(), characterLiteral(), integerLiteral(),
             unaryOperator(hasAnyOperatorName("+", "-"),
                           hasUnaryOperand(integerLiteral())),
             floatLiteral(),
             unaryOperator(hasAnyOperatorName("+", "-"),
                           hasUnaryOperand(floatLiteral())),
             cxxBoolLiteral(), cxxNullPtrLiteralExpr(), implicitValueInitExpr(),
-            initListExpr(), declRefExpr(to(enumConstantDecl())));
+            declRefExpr(to(enumConstantDecl())));
+
+  auto Init =
+      anyOf(initListExpr(anyOf(
+                allOf(initCountIs(1), hasInit(0, ignoringImplicit(InitBase))),
+                initCountIs(0))),
+            InitBase);
 
   Finder->addMatcher(
       cxxConstructorDecl(
           isDefaultConstructor(), unless(isInstantiated()),
           forEachConstructorInitializer(
               cxxCtorInitializer(
                   forField(unless(anyOf(getLangOpts().CPlusPlus2a
                                             ? unless(anything())

clang-tools-extra/test/clang-tidy/checkers/modernize-use-default-member-init.cpp

 // RUN: %check_clang_tidy -std=c++11,c++14,c++17 %s modernize-use-default-member-init %t -- -- -fexceptions
 // FIXME: Fix the checker to work in C++2a mode.
 
 struct S {
 };
 
 struct PositiveValueChar {
   PositiveValueChar() : c0(), c1()/*, c2(), c3()*/ {}
   // CHECK-FIXES: PositiveValueChar()  {}
public:
   catch (...) {}
 
 private:
   int i, k;
   // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: use default member initializer for 'i' [modernize-use-default-member-init]
   // CHECK-MESSAGES: :[[@LINE-2]]:10: warning: use default member initializer for 'k' [modernize-use-default-member-init]
   // CHECK-FIXES: int i{5}, k{8};
 };
+
+struct PR45363 {
+  // Ensure no warning is emitted here
+  PR45363(int i = 0) : m_i{i} {}
+  int m_i;
+};
+
+struct EmptyBracedIntDefault {
+  EmptyBracedIntDefault() : m_i{} {}
+  int m_i;
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: use default member initializer for 'm_i' [modernize-use-default-member-init]
+  // CHECK-FIXES:      {{^  }}EmptyBracedIntDefault()  {}
+  // CHECK-FIXES-NEXT: {{^  }}int m_i{};
+};