[cfe-dev] ParseClassSpecifier: can "unions" inherit?

[Ted Kremenek]

On Sep 4, 2008, at 9:45 AM, Doug Gregor wrote:

> On Thu, Sep 4, 2008 at 12:01 PM, Ted Kremenek <kremenek at apple.com>  
> wrote:
>> I just noticed the following code fragment in ParseClassSpecifier:
>>
>>  // Parse the tag portion of this.
>>  DeclTy *TagDecl = Actions.ActOnTag(CurScope, TagType, TK, StartLoc,
>> Name,
>>                                     NameLoc, Attr);
>>
>>  // Parse the optional base clause (C++ only).
>>  if (getLang().CPlusPlus && Tok.is(tok::colon)) {
>>    ParseBaseClause(TagDecl);
>>  }
>>
>> It appears from the code that the 'if' branch can be taken even if  
>> the
>> tag decl is a union.  Is this valid in the C++ grammar?  That is, can
>> there be a "base clause" for unions in C++, and if so, what does that
>> mean?
>
> In the C++ grammar, unions can have base classes, but it's
> semantically incorrect according to [class.union]p1. So, the parser
> parses it and Sema gives an error (see Sema::ActOnBaseSpecifier).
>
>  - Doug

Okay, that makes sense.  If the Parser is suppose to strictly follow  
the grammar then it makes sense why the error is handled in Sema.