[cfe-dev] AST representation for parentheses inside types.

[Enea Zaffanella]

Il 09/12/2010 16:08, Douglas Gregor ha scritto:
> 
> On Dec 8, 2010, at 12:02 PM, Enea Zaffanella wrote:
> 
>> Il 07/12/2010 18:36, Douglas Gregor ha scritto:
>>>
>>> On Dec 7, 2010, at 6:39 AM, Enea Zaffanella wrote:
>>>
>>>> Hello.
>>>>
>>>> We noticed some time ago that the AST representation used in clang does
>>>> not allow for the representation of those pairs of parentheses that can
>>>> occur inside a syntactic type. For instance, the following C code:
>>>>
>>>> void ((((*fun_ptr))))(void);
>>>> int (*(int_arr_ptr))[15];
>>>> void (((*((*fun_ptr_arr_ptr)[10]))))(int, int);
>>>> int ((a));
>>>>
>>>> is printed (using -ast-print) as follows
>>>>
>>>> void (*fun_ptr)(void);
>>>> int (*int_arr_ptr)[15];
>>>> void (*(*fun_ptr_arr_ptr)[10])(int, int);
>>>> int a;
>>>>
>>>> The printed parentheses are not directly represented in the AST: they
>>>> are inserted by the pretty printer (to respect precedence).
>>>>
>>>> Are there plans to extend the AST in order to faithfully represent the
>>>> code above?
>>>
>>> Not that I know of.
>>>
>>>> To our eyes, it seems that the Type hierarchy should be enriched by
>>>> adding a ParenType derived class (similar to the ParenExpr class for the
>>>> Expr hierarchy). A ParenType would always be a non-canonical type and
>>>> the corresponding ParenTypeLoc would provide locations for the two
>>>> parentheses. At the parser level, we would have another kind of
>>>> DeclaratorChunk.
>>>>
>>>> Would this approach make sense?
>>>
>>> Yes, this approach makes sense to me.
>>>
>>> 	- Doug
>>
>> OK, here is attached a patch along the sketch mentioned above.
>> It passes all clang tests but a single one.
> 
> Looks great, with one comment below about the failing test.
> 
>> The failing test is something related to ObjC, on which I have very
>> little confidence. Apparently, it seems that we should adjust the
>> expected output, which currently is as follows:
>>
>> FunctionDecl:{ResultType void}{TypedText f}{LeftParen (}{Placeholder
>> ^int(int x, int y)block}{RightParen )} (50)
>>
>> whereas we now obtain an extra pair of parentheses:
>>
>> FunctionDecl:{ResultType void}{TypedText f}{LeftParen (}{Placeholder int
>> (^)(int, int)}{RightParen )} (50)
> 
> This probably just means that we need to look through ParenTypeLocs within the FormatFunctionParameter routine in SemaCodeComplete.cpp.

Right, we were missing that source file.
Now even that one test passes.

>> We look forward for suggestions/corrections/etc.
> 
> How many parenthesized types do you see in a typical .c or .cpp file?
> 
> 	- Doug

Well, of course the answer will depend on the meaning of "typical", but
anyway my guess is that they should be very few. Is it just curiosity or
are you really worried about the memory space impact?

Enea.