[clang-tidy] Ignore empty members and bases in cppcoreguidelines-pro-type-member-init

[malcolm.parsons]

Summary

Empty/incomplete variables/members/bases don't need to be initialized

[aaron.ballman]

LGTM, with one small commenting nit.

clang-tidy/cppcoreguidelines/ProTypeMemberInitCheck.cpp

320 ↗

(On Diff #73485)

Comments should be complete sentences (capitalization, punctuation, etc), however, I'm not certain that this comment adds value as is. I would mark it a FIXME because copy-paste code is bad.

[malcolm.parsons]

Mark comment as FIXME.

[alexfh]

LG

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

if (const auto *Ctor = Result.Nodes.getNodeAs<CXXConstructorDecl>("ctor")) {
     checkUninitializedTrivialType(*Result.Context, Var);
   }
 }
 
 void ProTypeMemberInitCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
   Options.store(Opts, "IgnoreArrays", IgnoreArrays);
 }
 
+// FIXME: Copied from clang/lib/Sema/SemaDeclCXX.cpp.
+static bool isIncompleteOrZeroLengthArrayType(ASTContext &Context, QualType T) {
+  if (T->isIncompleteArrayType())
+    return true;
+
+  while (const ConstantArrayType *ArrayT = Context.getAsConstantArrayType(T)) {
+    if (!ArrayT->getSize())
+      return true;
+
+    T = ArrayT->getElementType();
+  }
+
+  return false;
+}
+
+static bool isEmpty(ASTContext &Context, const QualType &Type) {
+  if (const CXXRecordDecl *ClassDecl = Type->getAsCXXRecordDecl()) {
+    return ClassDecl->isEmpty();
+  }
+  return isIncompleteOrZeroLengthArrayType(Context, Type);
+}
+
 void ProTypeMemberInitCheck::checkMissingMemberInitializer(
     ASTContext &Context, const CXXRecordDecl &ClassDecl,
     const CXXConstructorDecl *Ctor) {
   bool IsUnion = ClassDecl.isUnion();
 
   if (IsUnion && ClassDecl.hasInClassInitializer())
     return;
 
   // Gather all fields (direct and indirect) that need to be initialized.
   SmallPtrSet<const FieldDecl *, 16> FieldsToInit;
   forEachField(ClassDecl, ClassDecl.fields(), false, [&](const FieldDecl *F) {
     if (!F->hasInClassInitializer() &&
         utils::type_traits::isTriviallyDefaultConstructible(F->getType(),
-                                                            Context))
+                                                            Context) &&
+        !isEmpty(Context, F->getType()))
       FieldsToInit.insert(F);
   });
   if (FieldsToInit.empty())
     return;
 
   if (Ctor) {
     for (const CXXCtorInitializer *Init : Ctor->inits()) {
       // Remove any fields that were explicitly written in the initializer list

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

#define UNINITIALIZED_FIELD_IN_MACRO_BODY_VIRTUAL(FIELD) \
   };                                                     \
 // Ensure FIELD is not initialized since fixes inside of macros are disabled.
 // CHECK-FIXES: int FIELD;
 
 UNINITIALIZED_FIELD_IN_MACRO_BODY_VIRTUAL(F);
 // CHECK-MESSAGES: :[[@LINE-1]]:1: warning: constructor does not initialize these fields: F
 UNINITIALIZED_FIELD_IN_MACRO_BODY_VIRTUAL(G);
 // CHECK-MESSAGES: :[[@LINE-1]]:1: warning: constructor does not initialize these fields: G
+
+struct NegativeEmpty {
+};
+
+static void NegativeEmptyVar() {
+  NegativeEmpty e;
+  (void)e;
+}
+
+struct NegativeEmptyMember {
+  NegativeEmptyMember() {}
+  NegativeEmpty e;
+};
+
+struct NegativeEmptyBase : NegativeEmpty {
+  NegativeEmptyBase() {}
+};
+
+struct NegativeEmptyArrayMember {
+  NegativeEmptyArrayMember() {}
+  char e[0];
+};
+
+struct NegativeIncompleteArrayMember {
+  NegativeIncompleteArrayMember() {}
+  char e[];
+};