[clang] Factor out isCapturelessLambda

This changes the behavior of the call-site in "CodeGenFunction.cpp",
I think for the better. But I couldn't figure out how to test that
codepath.

Author: AMP999

clang/include/clang/AST/DeclCXX.h

@@ -1052,6 +1052,12 @@ class CXXRecordDecl : public RecordDecl {
     return static_cast<LambdaCaptureDefault>(getLambdaData().CaptureDefault);
   }
 
+  bool isCapturelessLambda() const {
+    if (!isLambda())
+      return false;
+    return getLambdaCaptureDefault() == LCD_None && capture_size() == 0;
+  }
+
   /// Set the captures for this lambda closure type.
   void setCaptures(ASTContext &Context, ArrayRef<LambdaCapture> Captures);
 

clang/lib/AST/DeclCXX.cpp

@@ -686,7 +686,7 @@ bool CXXRecordDecl::lambdaIsDefaultConstructibleAndAssignable() const {
   // C++17 [expr.prim.lambda]p21:
   //   The closure type associated with a lambda-expression has no default
   //   constructor and a deleted copy assignment operator.
-  if (getLambdaCaptureDefault() != LCD_None || capture_size() != 0)
+  if (!isCapturelessLambda())
     return false;
   return getASTContext().getLangOpts().CPlusPlus20;
 }

clang/lib/AST/Type.cpp

@@ -2664,8 +2664,7 @@ HasNonDeletedDefaultedEqualityComparison(const CXXRecordDecl *Decl) {
   if (Decl->isUnion())
     return false;
   if (Decl->isLambda())
-    return Decl->captures().empty() &&
-           (Decl->getLambdaCaptureDefault() == LCD_None);
+    return Decl->isCapturelessLambda();
 
   auto IsDefaultedOperatorEqualEqual = [&](const FunctionDecl *Function) {
     return Function->getOverloadedOperator() ==

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -1216,11 +1216,10 @@ void CodeGenFunction::StartFunction(GlobalDecl GD, QualType RetTy,
       SkippedChecks.set(SanitizerKind::ObjectSize, true);
       QualType ThisTy = MD->getThisType();
 
-      // If this is the call operator of a lambda with no capture-default, it
+      // If this is the call operator of a lambda with no captures, it
       // may have a static invoker function, which may call this operator with
       // a null 'this' pointer.
-      if (isLambdaCallOperator(MD) &&
-          MD->getParent()->getLambdaCaptureDefault() == LCD_None)
+      if (isLambdaCallOperator(MD) && MD->getParent()->isCapturelessLambda())
         SkippedChecks.set(SanitizerKind::Null, true);
 
       EmitTypeCheck(

clang/lib/Sema/SemaLambda.cpp

@@ -393,8 +393,7 @@ void Sema::DiagnoseInvalidExplicitObjectParameterInLambda(
   CXXRecordDecl *RD = Method->getParent();
   if (Method->getType()->isDependentType())
     return;
-  if (RD->getLambdaCaptureDefault() == LambdaCaptureDefault::LCD_None &&
-      RD->capture_size() == 0)
+  if (RD->isCapturelessLambda())
     return;
   QualType ExplicitObjectParameterType = Method->getParamDecl(0)
                                              ->getType()