[clang-tidy] Ignore other members in a union if any member of it is i…

…nitialized in cppcoreguidelines-pro-type-member-init

If a union member is initialized, other members are still recorded in the container to be initialized.  This patch fixes this behavior.
Reference issue: #54748

Differential Revision: https://reviews.llvm.org/D127293

clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeMemberInitCheck.cpp

@@ -61,6 +61,17 @@ void forEachFieldWithFilter(const RecordDecl &Record, const T &Fields,
   }
 }
 
+void removeFieldInitialized(const FieldDecl *M,
+                            SmallPtrSetImpl<const FieldDecl *> &FieldDecls) {
+  const RecordDecl *R = M->getParent();
+  if (R && R->isUnion()) {
+    // Erase all members in a union if any member of it is initialized.
+    for (const auto *F : R->fields())
+      FieldDecls.erase(F);
+  } else
+    FieldDecls.erase(M);
+}
+
 void removeFieldsInitializedInBody(
     const Stmt &Stmt, ASTContext &Context,
     SmallPtrSetImpl<const FieldDecl *> &FieldDecls) {
@@ -70,7 +81,7 @@ void removeFieldsInitializedInBody(
                 hasLHS(memberExpr(member(fieldDecl().bind("fieldDecl")))))),
             Stmt, Context);
   for (const auto &Match : Matches)
-    FieldDecls.erase(Match.getNodeAs<FieldDecl>("fieldDecl"));
+    removeFieldInitialized(Match.getNodeAs<FieldDecl>("fieldDecl"), FieldDecls);
 }
 
 StringRef getName(const FieldDecl *Field) { return Field->getName(); }
@@ -418,13 +429,18 @@ void ProTypeMemberInitCheck::checkMissingMemberInitializer(
 
   // Gather all fields (direct and indirect) that need to be initialized.
   SmallPtrSet<const FieldDecl *, 16> FieldsToInit;
-  forEachField(ClassDecl, ClassDecl.fields(), [&](const FieldDecl *F) {
+  bool AnyMemberHasInitPerUnion = false;
+  forEachFieldWithFilter(ClassDecl, ClassDecl.fields(),
+                         AnyMemberHasInitPerUnion, [&](const FieldDecl *F) {
     if (IgnoreArrays && F->getType()->isArrayType())
       return;
+    if (F->hasInClassInitializer() && F->getParent()->isUnion())
+      AnyMemberHasInitPerUnion = true;
     if (!F->hasInClassInitializer() &&
         utils::type_traits::isTriviallyDefaultConstructible(F->getType(),
                                                             Context) &&
-        !isEmpty(Context, F->getType()) && !F->isUnnamedBitfield())
+        !isEmpty(Context, F->getType()) && !F->isUnnamedBitfield() &&
+        !AnyMemberHasInitPerUnion)
       FieldsToInit.insert(F);
   });
   if (FieldsToInit.empty())
@@ -437,7 +453,7 @@ void ProTypeMemberInitCheck::checkMissingMemberInitializer(
       if (Init->isAnyMemberInitializer() && Init->isWritten()) {
         if (IsUnion)
           return; // We can only initialize one member of a union.
-        FieldsToInit.erase(Init->getAnyMember());
+        removeFieldInitialized(Init->getAnyMember(), FieldsToInit);
       }
     }
     removeFieldsInitializedInBody(*Ctor->getBody(), Context, FieldsToInit);
@@ -478,7 +494,7 @@ void ProTypeMemberInitCheck::checkMissingMemberInitializer(
   // Collect all fields but only suggest a fix for the first member of unions,
   // as initializing more than one union member is an error.
   SmallPtrSet<const FieldDecl *, 16> FieldsToFix;
-  bool AnyMemberHasInitPerUnion = false;
+  AnyMemberHasInitPerUnion = false;
   forEachFieldWithFilter(ClassDecl, ClassDecl.fields(),
                          AnyMemberHasInitPerUnion, [&](const FieldDecl *F) {
     if (!FieldsToInit.count(F))

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines-pro-type-member-init.cpp

@@ -552,3 +552,21 @@ union U2 {
   int A;
   // CHECK-FIXES-NOT: int A{};
 };
+
+struct S1 {
+  S1() {}
+  // CHECK-MESSAGES-NOT: warning:
+  union {
+    int a = 0;
+    int b;
+  };
+};
+
+struct S2 {
+  S2() : a{} {}
+  // CHECK-MESSAGES-NOT: warning:
+  union {
+    int a;
+    int b;
+  };
+};