[clang-tidy] Handle bitfields in cppcoreguidelines-pro-type-member-init

[malcolm.parsons]

Summary

Unnamed bitfields cannot be initialized.
Bitfields cannot be in-class initialized.

[aaron.ballman]

LGTM!

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

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) &&
-        !isEmpty(Context, F->getType()))
+        !isEmpty(Context, F->getType()) && !F->isUnnamedBitfield())
       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
void ProTypeMemberInitCheck::checkMissingMemberInitializer(
   if (Ctor && Ctor->getLocStart().isMacroID())
     return;
 
   // 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;
   forEachField(ClassDecl, FieldsToInit, true, [&](const FieldDecl *F) {
     // Don't suggest fixes for enums because we don't know a good default.
-    if (!F->getType()->isEnumeralType())
+    // Don't suggest fixes for bitfields because in-class initialization is not
+    // possible.
+    if (!F->getType()->isEnumeralType() && !F->isBitField())
       FieldsToFix.insert(F);
   });
   if (FieldsToFix.empty())
     return;
 
   // Use in-class initialization if possible.
   if (Context.getLangOpts().CPlusPlus11) {
     for (const FieldDecl *Field : FieldsToFix) {

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

struct NegativeIncompleteArrayMember {
   char e[];
 };
 
 template <typename T> class NoCrash {
   class B : public NoCrash {
     template <typename U> B(U u) {}
   };
 };
+
+struct PositiveBitfieldMember {
+  PositiveBitfieldMember() {}
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: constructor does not initialize these fields: F
+  unsigned F : 5;
+};
+
+struct NegativeUnnamedBitfieldMember {
+  NegativeUnnamedBitfieldMember() {}
+  unsigned : 5;
+};
+
+struct NegativeInitializedBitfieldMembers {
+  NegativeInitializedBitfieldMembers() : F(3) { G = 2; }
+  unsigned F : 5;
+  unsigned G : 5;
+};