translate-c: error: expected pointer, found '?[*c]c_int'

[sigod]

Zig Version

0.9.0-dev.1324+598db831f

Steps to Reproduce

I'm trying to save a PNG file with stb_image_write library:

const c = @cImport({
    @cDefine("STB_IMAGE_WRITE_IMPLEMENTATION", {});
    @cInclude("stb_image_write.h");
});

pub fn main() anyerror!void {
    const pixels: []u8 = &.{};
    if (c.stbi_write_png("out.png", 1920, 1024, 4, pixels.ptr, 0) == 0) {
        return error.StbiError;
    }
}

Expected Behavior

Expected it to successfully compile. As it does with stbi_write_jpg, for example.

Actual Behavior

It fails with:

.\zig-cache\o\b776ce5469cb6475122be6741d09298f\cimport.zig:2209:50: error: expected pointer, found '?[*c]c_int'
    var p: ?*c_void = realloc(@ptrCast(?*c_void, if (arr.* != null) @ptrCast([*c]c_int, @alignCast(@import("std").meta.alignment(c_int), arr.*)) - @bitCast(usize, @intCast(isize, @as(c_int, 2))) else null), @bitCast(c_ulonglong, @as(c_longlong, itemsize * m)) +% (@sizeOf(c_int) *% @bitCast(c_ulonglong, @as(c_longlong, @as(c_int, 2)))));
                                                 ^
.\zig-cache\o\b776ce5469cb6475122be6741d09298f\cimport.zig:2209:31: note: referenced here
    var p: ?*c_void = realloc(@ptrCast(?*c_void, if (arr.* != null) @ptrCast([*c]c_int, @alignCast(@import("std").meta.alignment(c_int), arr.*)) - @bitCast(usize, @intCast(isize, @as(c_int, 2))) else null), @bitCast(c_ulonglong, @as(c_longlong, itemsize * m)) +% (@sizeOf(c_int) *% @bitCast(c_ulonglong, @as(c_longlong, @as(c_int, 2)))));
                              ^

Looks like the issue is with line 829:

void *p = STBIW_REALLOC_SIZED(*arr ? stbiw__sbraw(*arr) : 0, *arr ? (stbiw__sbm(*arr)*itemsize + sizeof(int)*2) : 0, itemsize * m + sizeof(int)*2);

[sigod]

I should mention, it also prints this error:

...\zig\lib\std\meta.zig:122:37: error: no align available for type 'c_void'
        .Optional => |info| switch (@typeInfo(info.child)) {
                                    ^
.\zig-cache\o\b776ce5469cb6475122be6741d09298f\cimport.zig:2444:496: note: called from here
        _ = if ((out == null) or (((@ptrCast([*c]c_int, @alignCast(@import("std").meta.alignment(c_int), @ptrCast(?*c_void, out))) - @bitCast(usize, @intCast(isize, @as(c_int, 2))))[@intCast(c_uint, @as(c_int, 1))] + @as(c_int, 1)) >= (@ptrCast([*c]c_int, @alignCast(@import("std").meta.alignment(c_int), @ptrCast(?*c_void, out))) - @bitCast(usize, @intCast(isize, @as(c_int, 2))))[@intCast(c_uint, @as(c_int, 0))])) stbiw__sbgrowf(@ptrCast([*c]?*c_void, @alignCast(@import("std").meta.alignment(?*c_void), &out)), @as(c_int, 1), @bitCast(c_int, @truncate(c_uint, @sizeOf(u8)))) else null;
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               ^
.\zig-cache\o\b776ce5469cb6475122be6741d09298f\cimport.zig:2292:130: note: called from here
pub fn stbi_zlib_compress(arg_data: [*c]u8, arg_data_len: c_int, arg_out_len: [*c]c_int, arg_quality: c_int) callconv(.C) [*c]u8 {
                                                                                                                                 ^
...\zig\lib\std\meta.zig:120:49: note: referenced here
pub fn alignment(comptime T: type) comptime_int {
                                                ^
...\zig\lib\std\meta.zig:123:39: note: referenced here
            .Pointer, .Fn => alignment(info.child),
                                      ^
.\zig-cache\o\b776ce5469cb6475122be6741d09298f\cimport.zig:2444:496: note: referenced here
        _ = if ((out == null) or (((@ptrCast([*c]c_int, @alignCast(@import("std").meta.alignment(c_int), @ptrCast(?*c_void, out))) - @bitCast(usize, @intCast(isize, @as(c_int, 2))))[@intCast(c_uint, @as(c_int, 1))] + @as(c_int, 1)) >= (@ptrCast([*c]c_int, @alignCast(@import("std").meta.alignment(c_int), @ptrCast(?*c_void, out))) - @bitCast(usize, @intCast(isize, @as(c_int, 2))))[@intCast(c_uint, @as(c_int, 0))])) stbiw__sbgrowf(@ptrCast([*c]?*c_void, @alignCast(@import("std").meta.alignment(?*c_void), &out)), @as(c_int, 1), @bitCast(c_int, @truncate(c_uint, @sizeOf(u8)))) else null;
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               ^

I'm not sure if they're separate or related.

[akovaski]

I'm not familiar enough with Zig to suggest or make a fix here, but I have generated minimal reproducible examples of the above errors.

error: expected pointer, found '?[*c]c_int'

source code

void *repr_9917_a(int *arr, int check)
{
   void *p = check ? arr : 0;
   return p;
}

translated code

pub export fn repr_9917_a(arg_arr: [*c]c_int, arg_check: c_int) ?*c_void {
    var arr = arg_arr;
    var check = arg_check;
    var p: ?*c_void = @ptrCast(?*c_void, if (check != 0) arr else null);
    return p;
}

error

zig-cache/o/3c589d970733d4f2f8b3fecc1a600c26/cimport.zig:53:42: error: expected pointer, found '?[*c]c_int'
    var p: ?*c_void = @ptrCast(?*c_void, if (check != 0) arr else null);
                                         ^
zig-cache/o/3c589d970733d4f2f8b3fecc1a600c26/cimport.zig:53:23: note: referenced here
    var p: ?*c_void = @ptrCast(?*c_void, if (check != 0) arr else null);

error: no align available for type 'c_void'

source code

void ** repr_9917_b(char **out)
{
   void **r = (void **) out;
   return r;
}

translated code

pub export fn repr_9917_b(arg_out: [*c][*c]u8) [*c]?*c_void {
    var out = arg_out;
    var r: [*c]?*c_void = @ptrCast([*c]?*c_void, @alignCast(@import("std").meta.alignment(?*c_void), out));
    return r;
}

error

/opt/zig-linux-x86_64-0.9.0-dev.1343+75cecef63/lib/std/meta.zig:121:37: error: no align available for type 'c_void'
        .Optional => |info| switch (@typeInfo(info.child)) {
                                    ^
zig-cache/o/d2febc8073dcce122a9eb979e2172b63/cimport.zig:58:90: note: called from here
    var r: [*c]?*c_void = @ptrCast([*c]?*c_void, @alignCast(@import("std").meta.alignment(?*c_void), out));
                                                                                         ^
zig-cache/o/d2febc8073dcce122a9eb979e2172b63/cimport.zig:56:61: note: called from here
pub export fn repr_9917_b(arg_out: [*c][*c]u8) [*c]?*c_void {
                                                            ^
/opt/zig-linux-x86_64-0.9.0-dev.1343+75cecef63/lib/std/meta.zig:119:49: note: referenced here
pub fn alignment(comptime T: type) comptime_int {
                                                ^
/opt/zig-linux-x86_64-0.9.0-dev.1343+75cecef63/lib/std/meta.zig:122:39: note: referenced here
            .Pointer, .Fn => alignment(info.child),
                                      ^
zig-cache/o/d2febc8073dcce122a9eb979e2172b63/cimport.zig:58:90: note: referenced here
    var r: [*c]?*c_void = @ptrCast([*c]?*c_void, @alignCast(@import("std").meta.alignment(?*c_void), out));
                                                                                         ^

Some random references

#4686 - using normal pointers (rather than c pointers) for pointers to opaque types
#2318 - translate-c pointer alignment
ae15022 - translate-c: Fix casting of function pointers

[Vexu]

The first issue is a bug in peer type resolution @TypeOf(if (check != 0) arr else null) should be [*c]c_int.
The second one is a bug in translate-c only considering one level of indirection.