[nicl] RFR: Support UnexposedDecl

[Maurizio Cimadamore]

On 23/05/18 15:32, Henry Jen wrote:
>> On May 23, 2018, at 1:37 AM, Maurizio Cimadamore <maurizio.cimadamore at oracle.com> wrote:
>>
>> Looks sensible.
>>
>> Another, more implicit way to get there would be to enable this behavior only inside ' extern "C" ' blocks. E.g. teach jextract about the usual dance, and change interpretation for prototype-less function inside those boundaries. (and maybe have a flag that allows for overriding this kind of inference).
>>
> We only see extern “C” in C++ mode, not in regular C mode in the way we use libclang.
Ah - I see
>
> I’ll push the current webrev if there is no objection and then we can think of the switch or other proposal make more sense to developers.
Ok

Maurizio
>
> Cheers,
> Henry
>
>> Maurizio
>>
>>
>> On 23/05/18 05:08, Henry Jen wrote:
>>> Hi,
>>>
>>> C allows K&R style function declaration, although is obsolete. Such declaration is considered non-prototype function declaration. Compile with -Wstrict-prototypes in clang will emit warnings.
>>>
>>> However, many C++ code when providing C binding will use this form instead of int func(void) because that’s exactly what it should be in C++ and -Wstrict-prototypes for C is off by default.
>>>
>>> So, consider following C header file which is actually quite often from C++ developer, who may consider writing int func(void) redundant,
>>>
>>> #ifdef __cplusplus
>>> extern “C” {
>>> #endif
>>>
>>> int func();
>>>
>>> #ifdef __cplusplus
>>> }
>>> #endif
>>>
>>> jextract will need to deal with that situation. With proposed webrev[1], developer can run jextract with C++ mode by passing ‘-C -x -C c++’, this is essential forcing libclang to parse header using c++ syntax. This is not too bad as eventually we will support c++, but there could be unexpected side-effects as jextract cannot deal with all c++ syntax yet. However, this is no worse than using jextract against a .hpp file.
>>>
>>> When running in c++ mode, the extern “C” would be a UnexposedDecl, the webrev add support for that.
>>>
>>> [1] http://cr.openjdk.java.net/~henryjen/panama/namespace/webrev/
>>>
>>> I would like to propose additional follow up by adding a switch —noKR(name is up to discussion). Developer can use that switch if he is certain the header file is not using K&R style prototype. In this case, we simply consider all non-prototype function declaration as no argument function prototype. Then we still parsing use C mode which should be less surprising. What do you think?
>>>
>>> The change is made for nicl branch, I will port into foreign branch later with a couple other fixes for nicl in queue.
>>>
>>> Cheers,
>>> Henry
>>>