[cfe-dev] Implicitly declared K&R parameters.

[Enea Zaffanella]

Douglas Gregor wrote:
> On Sep 29, 2010, at 5:11 AM, Enea Zaffanella wrote:
> 
>> Hello.
>> 
>> Consider the following K&R function definition:
>> 
>> void foo(implicit, explicit) int explicit; {}

[...]

>> bool implicit = (param.getLocation() == param.getTypeSpecStartLoc());
>> 
>> This was working as expected on the few tests we tried. However, we
>> would like to avoid making wild guesses: is such a property a valid
>> (i.e., supported) clang invariant or is it just working by chance?
> 
> It probably comes from building a "trivial" TypeSourceInfo for the
> parameter type, using the location of the identifier. It's somewhat
> of an accident, but it's also unlikely to change.
> 
>> For clarity, would you accept the addition of a method
>> 
>> bool ParmVarDecl::isImplicitIntKNRParameter() const { return
>> getLocation() == getTypeSpecTypeLoc(); }
>> 
>> ?
> 
> 
> There are likely to be other implicitly-generated ParmVarDecls that
> are likely to be caught by this, e.g., the ParmVarDecls for an
> implicitly-generated copy constructor or copy assignment operator. At
> the very least, this should check that getLocation() is valid and
> that the parameter is from a K&R function definition.
> 
> However, I do wonder you're really trying to solve the larger problem
> of "implicit int", which would likely require something completely
> different. For example, here's some ugly C89 code:
> 
> f(x, y) { register z = x + y; return z; }
> 
> We'll don't keep track of the implicit int in f, x, y, or z. So,
> while I'm not opposed to the method you're suggesting (with fixes), I
> think it's only solving part of the problem that you're probably
> working on.
> 
> - Doug

If we _always_ have a (trivial) TypeSourceInfo,
then the "implicit int" could be detected by checking

   const WrittenBuiltinSpecs&
   BuiltinTypeLoc::getWrittenBuiltinSpecs() const;

In C, if the (return) type is int and there is no written type specifier 
and no written sign specifier, then it must have been an implicit int.
But what if we do not have a TypeSourceInfo set?

Enea.