[cfe-dev] [RFC] Preliminary patch to support MSVC __declspec(property)

[Francois Pichet]

On Sat, Dec 22, 2012 at 10:11 AM, endlessroad1991 at gmail.com <
endlessroad1991 at gmail.com> wrote:

> Some guy from PathScale told me that AMP headers doesn't contain
> subscriptable property. And I looked at ATL headers, neither do they. So
> for these purposed, subscriptable property is not necessary.
> And I still think that subscriptable property is kind of messy...
> So I only implement non-subscriptable property.
>
> Brief:
> - Add a MSPropertyDecl, parallel to FieldDecl. Now property is separated
> from Field.
> - Add a MSPropertyRefExpr. It seems to be necessary, because we can't just
> create a PseudoObjectExpr.
>
> Current status:
> - Non-subscriptable property only.
> - Property can be inherited.
> - Get, Set, =, +=/-=/..., ++/-- works correctly.
> - Property type can be incomplete type, as function return type.
>
> Patch, and a "difficult" testcase attached.
> I'm quite happy with this version, because it's much simpler and cleaner.
> John - Thank you very much, for the MSPropertyDecl and PseudoObjectExpr
> tips. They are really crucial to this patch.
>


More comments:

+  NamedDecl *NewFD;
+  AttributeList *MSPropertyAttr = 0;
+  for (auto it = D.getDeclSpec().getAttributes().getList();
+       it != 0; it = it->getNext())
+    if (it->getName()->getName() == "property") {
+      MSPropertyAttr = it;
+      break;
+    }
+  if (MSPropertyAttr) {
+    llvm::StringRef GetterName = MSPropertyAttr->getScopeName() ?
+      MSPropertyAttr->getScopeName()->getName() : StringRef();
+    llvm::StringRef SetterName = MSPropertyAttr->getParameterName() ?
+      MSPropertyAttr->getParameterName()->getName() : StringRef();
+    NewFD = new (Context) MSPropertyDecl(Decl::MSProperty, Record, Loc,
+                                         II, T, TInfo, TSSL,
+                                         GetterName, SetterName);
+    NewFD->setAccess(AS);
+  } else {
+    NewFD = CheckFieldDecl(II, T, TInfo, Record, Loc, Mutable, BitWidth,
+                           InitStyle, TSSL, AS, PrevDecl, &D);
+  }

I think this code should be in Sema::ActOnCXXMemberDeclarator and not
in Sema::HandleField. A property is not a field and HandleField should
continue to return a FieldDecl*.

Also you need to protect this code with Sema.getOptions().MicrosoftExt


+static ExprResult
+BuildMSPropertyRefExpr(ASTContext &Context, Expr *BaseExpr, bool IsArrow,
+                       const DeclarationNameInfo &MemberNameInfo,
+                       MSPropertyDecl *PD) {
+  return new (Context) MSPropertyRefExpr(BaseExpr, PD, IsArrow,
+                                         Context.PseudoObjectTy, VK_LValue,

The type of the expression should be PD->getType() and not
Context.PseudoObjectTy.
Otherwise you won't be able to use a MSPropertyRefExpr in the context of a
larger expression.

For example:
class C {
public:
  int operator[](int i){ return i;}
};

struct S {
   C v;
   C getprop() { return v; }
   __declspec(property(get = getprop)) C the_prop;
};
int main()
{
   S s;
   int a = s.the_prop[3];
  printf("%d", a);
}
this must print 3.

This is *not* a property indexer. The result of the MSPropertyRefExpr
expression must be class C to allow for the operator[] to be used. C++ AMP
which use ms property extensively will contains code like that.
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