[nicl] RFR: Support UnexposedDecl

[Maurizio Cimadamore]

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).

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 C allows K&R style function declaration, although is obsolete.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
>