Unnamed struct members are skipped

[athre0z]

Unnamed nested structures/unions are currently skipped.

Given

struct Meow {
    int blah;
    union {
        float either1;
        int either2;
    };
    float moo;
};

the lib generates the following Julia code:

struct Meow
    blah::Cint
    moo::Cfloat
end

The problem goes away when giving the member a name. Maybe generating a member called something along the lines of "anon_0" for these unnamed nested items would be best?

[Gnimuc]

It's not easy to support this C11 feature using bare Julia struct since Julia's struct doesn't have this kinda feature. However, as Julia allows us to overload Base.getproperty, we could emulate this behavior. You could take this snippet as an example on how to emulate a C union in Julia.

In this way, non-canonical C structs/unions should be auto-generated as a struct with a single data byte field (e.g. struct Foo; data::NTuple{N,UInt8}); end) where the size N can be computed from Clang AST. The corresponding Base.getproperty function can also be generated basically in the same pattern. I guess __attribute__ identifiers(#224) can also be supported in a similar way.

To support this, wrap_c.jl needs to be refactored, but I currently don't have time to do this, so if your code only have a few C11 structures, the "best practice" for now is to overload Base.getproperty manually.

[athre0z]

Thank you for the quick & detailed response! Overloading getproperty is what I currently do. Auto-generating such methods in the long term sounds great in general -- this way, regular unions would become a lot nicer as well!

Since just skipping the member results in misaligned fields afterwards, for now, maybe adding a warning when encountering such unnamed fields would be a good thing -- or just generating a name for the field? In my case it was rather obvious, but other people might be less fortunate, not realizing why their struct fields are misaligned after a skipped field.

[Gnimuc]

Hi @athre0z, could you share a link to your wrapper repo? I'd like to give #278 a test. Any suggestions on how to overload Base.getproperty would be highly appreciated.

[athre0z]

Hi @Gnimuc! Unfortunately I don't remember where exactly I used that and I'm not even sure if this ever ended up in a commit, sorry! I think what I did was simply performing an if on the symbol, then have an unsafe_load for each field with a hard-coded struct offset.

[cdsousa]

Hi, I've just tried master branch with the code presented by the OP and it fails with ERROR: There is no definition for Meow's field: 's type: [`union Meow::(anonymous at ......
Is that expected?

[Gnimuc]

Which version are you using？ 令和4年8月24日(水) 2:01 Cristóvão Duarte Sousa ***@***.***>:

…

Hi, I've just tried master branch with the code presented by the OP and it fails with ERROR: There is no definition for Meow's field: 's type: [`union Meow::(anonymous at ...... Is that expected? — Reply to this email directly, view it on GitHub <#233 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABYXW5O7HP37HIUYRM5VV53V2T7VVANCNFSM4IN55NKQ> . You are receiving this because you modified the open/close state.Message ID: ***@***.***>

[cdsousa]

I've tried it with Clang 0.16.0 and the current master branch, within Julia 1.8.

[Gnimuc]

Could you share some info about the C header?

I just noticed you used the example in the OP.