[cfe-dev] Proposal to fix issue 7715

[Manuel Klimek]

ping

On Wed, Sep 22, 2010 at 7:08 PM, Manuel Klimek <klimek at google.com> wrote:
> On Mon, Sep 20, 2010 at 8:28 PM, Douglas Gregor <dgregor at apple.com> wrote:
>>
>> On Sep 14, 2010, at 7:39 AM, Manuel Klimek wrote:
>>
>>> Hi,
>>>
>>> I came up with a solution to http://llvm.org/bugs/show_bug.cgi?id=7715
>>> (clang++ gives wrong error about default argument in kdatetime.h), as
>>> talked about on IRC. It was a little more complicated than
>>> anticipated, as we need to keep the stack of scopes correct.
>>>
>>> I would like to get some feedback on the general direction /
>>> implementation of this patch. If we agree this is the way to go, I'd
>>> comment it more thoroughly and add some more regression tests.
>>
>> I like the general direction; there are a few comments below. Obviously, more comments and regression tests would be greatly appreciated!
>>
>>> I tried
>>> to keep the diff as small as possible, but my gut feeling would also
>>> lead me to put more stuff into the classes as opposed to having
>>> everything as methods on Parser. Not sure though.
>>
>> I'd rather keep the parsing and Sema-invoking code in the parser itself, although I admit it's mostly an aesthetic argument and it's not a strong preference.
>
> I trust your gut-feeling then ;)
>
>> A few small comments:
>>
>> diff --git a/include/clang/Parse/Parser.h b/include/clang/Parse/Parser.h
>> index a7dab1e..422adce 100644
>> --- a/include/clang/Parse/Parser.h
>> +++ b/include/clang/Parse/Parser.h
>> @@ -552,7 +552,30 @@ private:
>>   //===--------------------------------------------------------------------===//
>>   // Lexing and parsing of C++ inline methods.
>>
>> -  struct LexedMethod {
>> +  struct ParsingClass;
>> +
>> +  class LateParsedDeclaration {
>> +  public:
>> +    virtual ~LateParsedDeclaration();
>> +    virtual void ParseLexedDefaultArguments();
>> +    virtual void ParseLexedMethodDefs();
>> +  };
>>
>> I think the name ParseLexedDefaultArguments() is misleading, because default arguments aren't the only kind of thing that is delayed. C++ [class.mem]p1 also mentions function bodies (which we handle separately) and exception-specifications (which we don't handle)... the latter is why I'd prefer to keep a more generic name like "ParseLexedMethodDeclarations()".
>
> While trying to comment that part I got pretty confused by what you
> write. In the C++ standard I didn't find anything in [class.mem]p1
> that mentions function bodies (am I reading the wrong version?), but I
> find that in [class.mem]p2 it talks about "function bodies, default
> arguments and constructor ctor-initializers", where I'd expect
> ctor-initializers to be basically handled the same as function bodies.
> Where do exception specifications fall into all this?
>
> I called the methods ParseLexedDefaultArguments and
> ParseLexedMethodDefs as the function bodies must be parsed in a phase
> after all default arguments were parsed, since as far as I understand
> it the default arguments can always be used in the function bodies.
> I'd assume that anything else would be basically handled in a
> different phase, too.
> The interface is called LateParsedDeclaration (perhaps wanting a
> better name), as all the late parsed stuff is always combined with a
> method declaration, as far as I understood it.
>
> So overall I'm pretty confused and would appreciate some enlightenment ;)
>
> Thanks,
> /Manuel
>
>
>
>>
>> In Parser::ParseLexedMethodDeclaration(), we have:
>>
>> +      // Consume the '='.
>> +      assert(Tok.is(tok::equal) && "Default argument not starting with '='");
>> +      SourceLocation EqualLoc = ConsumeToken();
>> +
>> +      ExprResult DefArgResult(ParseAssignmentExpression());
>> +      if (DefArgResult.isInvalid())
>> +        Actions.ActOnParamDefaultArgumentError(LM.DefaultArgs[I].Param);
>> +      else {
>> +        if (Tok.is(tok::cxx_defaultarg_end))
>> +          ConsumeToken();
>> +        else
>> +          Diag(Tok.getLocation(), diag::err_default_arg_unparsed);
>> +        Actions.ActOnParamDefaultArgument(LM.DefaultArgs[I].Param, EqualLoc,
>> +                                          DefArgResult.take());
>> +      }
>>
>> There is (recently-added) code that enters the appropriate expression-evaluation context for default arguments, like this:
>>
>>        // The argument isn't actually potentially evaluated unless it is
>>        // used.
>>        EnterExpressionEvaluationContext Eval(Actions,
>>                                              Sema::PotentiallyEvaluatedIfUsed);
>>
>> Please make sure that gets into your patch.
>>
>> Thanks for tackling this! I look forward to your next revision; commenting/testing aside, it looks very close to being ready to commit.
>>
>>        - Doug
>
>
>
> --
> Manuel Klimek (http://go/klimek)
>



-- 
Manuel Klimek (http://go/klimek)