[cfe-dev] Patch adding a Boolean flag to TagDecl nodes.

[Douglas Gregor]

On Feb 3, 2010, at 2:01 PM, Abramo Bagnara wrote:

> Il 03/02/2010 21:42, Douglas Gregor ha scritto:
>> 
>> On Jan 29, 2010, at 12:10 PM, Enea Zaffanella wrote:
>> 
>>> Hello.
>>> 
>>> The attached patch adds a new Boolean flag to TagDecl nodes.
>>> 
>>> The new flag, named IsDefinedInDeclarator, tells whether or not the
>>> TagDecl is a definition that was syntactically occurring (possibly via
>>> macro expansions) in a declarator. Examples include tag types defined in
>>> function return types, function parameter types, variable or field
>>> declarations and type arguments of cast or sizeof expressions.
>>> 
>>> The new flag is meant to help clients such as code style checkers.
>> 
>> 
>> This feels like the wrong solution. I'd like to hear from others, but
>> the best approach seems to be to extend TagTypeLoc with a bit that
>> indicates whether this use of the tag type was a reference or a
>> definition. That way, a pretty-printer could know exactly where to
>> put the definition.
> 
> Our aim is exactly that and it works perfectly using the proposed patch:
> the RecordDecl inserted in DeclContext parsing
> 
> typedef struct s { int a; } x;
> 
> is marked with IsDefinedInDeclarator bit and then can be excluded from
> pretty printer output.

Ah, I understand the issue now. It's less about the problem of "does this typedef contain the definition of struct s?" and more about the problem of "was struct s defined by itself or as part of some other declaration?". My proposed solution didn't cover the latter at all.

> Next, analyzing TypedefDecl it could be easily
> verified that the location of TypedefDecl is the same of RecordDecl and
> then we can know easily that the record definition was embedded in the
> typedef declaration.
> 
> Parsing
> 
> struct s { int a; };
> typedef struct s x;
> 
> the RecordDecl is not marked and then the two declaration should not be
> grouped.
> 
> Following your proposal instead we have no way to understand that the
> RecordDecl in the former case should not be output (RecordDecl does not
> have TypeLoc where to store this info).
> 
> Take also in account that the bit you propose to add to typeloc is
> already deducible now using the location trick above.

Okay. Thank for you for the explanation. I've committed Enea's patch as r95586.

	- Doug