[Feature Request]: tooling to warn for 32 bit issues

[jabraham17]

I have had this same issue multiple times in the past week. The primary problem I have been having is calling extern C code with a Chapel type.

For example, the following code is perfectly fine on a 64 bit system because c_long is defined to be an int(64).

use CTypes;
//void myFunc(long x);
extern proc myFunc(x: c_long);

var x = 10;
myFunc(x);

But on a 32 bit system, c_long is a int(32), and so this code fails to compile.

It would be nice to have some kind of tooling (either a compiler warning or a lint warning) that you are trying to pass a Chapel int to a system dependent sized C int. I could imagine something that checks if a Chapel type is being passed to a type that resided in ChapelSysCTypes.

[bradcray]

What is the C prototype for myFunc()? (I'm guessing "simply long")? Do you control the C interface, or is it something from a library?

[jabraham17]

In my above example, yes the C prototype of myFunc would be long. I've updated the OP to make that clearer. The bug here is not in the C code, but rather its myFunc(x), because x is always a 64 bit integer.

I have hit this several times using the Python C API, which I have no control over.

[bradcray]

I agree it'd be nice to have tooling help with this. I'd argue that there isn't really a "bug" here, but that it's part of the ongoing pains that C signed themselves up for by not making their base types have well-defined size (exacerbated by people using them in public interfaces rather than the cstdint types instead). On past supercomputer systems, we used to have the opposite problem where the C compilers would define int to be 64-bits, and lots of existing code would assume it was 32 bits and break as a result.

The safe way to use such functions in Chapel would either be to declare x to be of type c_long as well or to always cast x to c_long when passing it to myFunc, either of which should make the code fully portable. That said, I realize that these are not very ergonomic, so am not suggesting that's what you (or an end-user) would necessarily would want to do.