attempt to use null value with `TranslateC`

[dotcarmen]

Zig Version

0.16.0-dev.452+1f7ee99b3

i'm on macos 26.0

Steps to Reproduce and Observed Behavior

minimal repro build.zig (i just used a foo.h with a single define):

const std = @import("std");

pub fn build(b: *std.Build) void {
    const optimize = b.standardOptimizeOption(.{});
    const target = b.standardTargetOptions(.{});

    const translate = b.addTranslateC(.{
        .root_source_file = b.path("foo.h"),
        .optimize = optimize,
        .target = target,
    });

    const output = translate.getOutput();
    const i = b.addInstallFile(output, "foo.zig");
    b.getInstallStep().dependOn(&i.step);
}

$ zig build
thread 7325870 panic: attempt to use null value
/Users/carmen/.zvm/master/lib/std/Build/Step/TranslateC.zig:200:46: 0x102fc36db in make (build)
    translate_c.output_file.path = output_dir.?.joinString(b.allocator, translate_c.out_basename) catch @panic("OOM");
                                             ^
/Users/carmen/.zvm/master/lib/std/Build/Step.zig:255:33: 0x102f5aa8f in make (build)
    const make_result = s.makeFn(s, options);
                                ^
/Users/carmen/.zvm/master/lib/compiler/build_runner.zig:1248:31: 0x102f39d6b in workerMakeOneStep (build)
    const make_result = s.make(.{
                              ^
/Users/carmen/.zvm/master/lib/std/Thread/Pool.zig:118:39: 0x102f3a51b in runFn (build)
            @call(.auto, func, closure.arguments);
                                      ^
/Users/carmen/.zvm/master/lib/std/Thread/Pool.zig:293:27: 0x102f76293 in worker (build)
            runnable.runFn(runnable, id);
                          ^
/Users/carmen/.zvm/master/lib/std/Thread.zig:511:13: 0x102f5823f in callFn__anon_72425 (build)
            @call(.auto, f, args);
            ^
/Users/carmen/.zvm/master/lib/std/Thread.zig:783:30: 0x102f38503 in entryFn (build)
                return callFn(f, args_ptr.*);
                             ^
???:?:?: 0x1929b8c07 in ??? (libsystem_pthread.dylib)
???:?:?: 0x1929b3ba7 in ??? (libsystem_pthread.dylib)
error: the following build command crashed:
.zig-cache/o/41dc0e498ae8896dedeb76e025cf4a9b/build /Users/carmen/.zvm/master/zig /Users/carmen/.zvm/master/lib /Users/carmen/tmp .zig-cache /Users/carmen/.cache/zig --seed 0xf529cc0e -Ze56f4a375ad03ecf

Expected Behavior

the above zig build command should succeed silently

[rpkak]

Seems to be caused by #24497.

zig/src/main.zig

Lines 4510 to 4519 in f624191

	fn cmdTranslateC(
	comp: *Compilation,
	arena: Allocator,
	fancy_output: ?*Compilation.CImportResult,
	file_system_inputs: ?*std.ArrayListUnmanaged(u8),
	prog_node: std.Progress.Node,
	) !void {
	dev.check(.translate_c_command);
	_ = file_system_inputs;
	_ = fancy_output;

cmdTranslateC just ignores fancy_output.

[HaraldWik]

when will this be fixed est?
I`m not very familiar with translate c development times

[numeralblue]

This prevented me from building after upgrading from 0.16.0-dev.235+377a8b2a3 to 0.16.0-dev.600+12ed0ff1e.

[kcbanner]

I started looking into this, and the strange this is that the translate-c process does exit successfully (I applied the patch from Vexu/arocc#895) - so it seems to be some kind of IPC issue with the sub-process not emitting the digest.

[kcbanner]

Ah, @rpkak was correct - the issue is that fancy_output is just left as undefined, so the output.errors.errorMessageCount() call crashes, and the digest is never served.

[rpkak]

@kcbanner

Ah, @rpkak was correct - the issue is that fancy_output is just left as undefined, so the output.errors.errorMessageCount() call crashes, and the digest is never served.

If I remember correctly it never crashes, because the capture option of jitCmd is null and because of this jitCmd decides to execv without a fork. jitCmd never returns.

You may want to try to remove some code duplication between Compilation.cImport and main.cmdTranslateC while working on this.

[kcbanner]

Thanks, yea I've started working on this - I'm taking a similar approach to what resonator does with a --zig-integration parameter that causes it to output an error bundle message on stdout.