translate-c: fix function pointer casting + alignCast and constCast at the same time

[paokitore]

This fixes ziglang/translate-c#45 and another issue I noticed: casting const void* to int* did not work.

Both of those issues are fixed with translate-c, so this PR might be useless though.

examples:

void *g = (void*)f;

used to translate to:

var g: ?*anyopaque = @as(?*anyopaque, @ptrCast(f));

forgetting a @constCast.

and

const void *c;
int *d = (int*)c;

the second line used to translate to:

var d: [*c]c_int = @as([*c]c_int, @ptrCast(@volatileCast(@constCast(c))));

forgetting a @alignCast.

[alexrp]

This would effectively be made obsolete by #24497, so I think we'd only consider taking this PR if #24497 for some reason fails to land in 0.15.0.

[paokitore]

The previous CI failed with 3 errors and the next one will still fail with 2 errors:

1. Formatting: I forgot and the last commit fixed it.

For the other two, I'd say that it's more of the tests' fault.

expected:

var func_ptr: ?*anyopaque = @as(?*anyopaque, @ptrCast(&foo));

got:

var func_ptr: ?*anyopaque = @as(?*anyopaque, @ptrCast(@volatileCast(@constCast(&foo))));

This fail is quite weird because the code expected by the test actually does not compile :

test1.zig:3:50: error: @ptrCast discards const qualifier
    var func_ptr: ?*anyopaque = @as(?*anyopaque, @ptrCast(&foo));
                                                 ^~~~~~~~~~~~~~
test1.zig:3:50: note: use @constCast to discard const qualifier

So I would say that this is an issue with the test.

expected:

@as([*c]c_int, @ptrCast(@volatileCast(@constCast(a))))

got:

@as([*c]c_int, @ptrCast(@volatileCast(@constCast(@alignCast(a)))))

I just have an extra @alignCast which still outputs valid zig code.
I don't think this in an issue, because there are many cases where an extra @alignCast is outputted:

typedef struct {
  int a;
} A;
void main() {
  int a = 3;
  int *a_ptr = &a;
  A *aa_ptr = (A*)a_ptr;
}

gets translated to

pub const A = extern struct {
    a: c_int = @import("std").mem.zeroes(c_int),
};
pub export fn main() void {
    var a: c_int = 3;
    _ = &a;
    var a_ptr: [*c]c_int = &a;
    _ = &a_ptr;
    var aa_ptr: [*c]A = @as([*c]A, @ptrCast(@alignCast(a_ptr)));
    _ = &aa_ptr;
}

even though c_int and A have the same alignment.

[alexrp]

Closing since we've switched to Aro-based translate-c as of #24497. Contributions to translate-c should now be opened on https://github.com/ziglang/translate-c.