Fuzz test runner causes assertion failure in `evalZigProcess`

[davnavr]

Zig Version

0.16.0-dev.1234+74900e938

Steps to Reproduce and Observed Behavior

With the following Zig program and build script:

// main.zig
const std = @import("std");

fn testOne(_: void, input: []const u8) !void {
    if (std.mem.eql(u8, "can you find me?", input)) {
        @trap();
    }
}

test {
    try std.testing.fuzz({}, testOne, .{});
}

// build.zig
const std = @import("std");

fn testOne(_: void, input: []const u8) !void {
    if (std.mem.eql(u8, "can you find me?", input)) {
        @trap();
    }
}

test {
    try std.testing.fuzz({}, testOne, .{});
}

Run zig build test --fuzz, which crashes with the following output:

info(web_server): web interface listening at http://[::1]:36383/
info(web_server): hint: pass '--webui=[::1]:36383' to use the same port next time
Build Summary: 3/3 steps succeeded; 1/1 tests passed
thread 3839 panic: reached unreachable code
/home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib/std/debug.zig:416:14: 0x10965d9 in assert (std.zig)
    if (!ok) unreachable; // assertion failure
             ^
/home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib/std/Build/Step.zig:406:11: 0x12a4a96 in evalZigProcess (std.zig)
    assert(s.result_failed_command == null);
          ^
/home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib/std/Build/Step/Compile.zig:1940:60: 0x12a7a81 in rebuildInFuzzMode (std.zig)
    const maybe_output_bin_path = try c.step.evalZigProcess(zig_args, progress_node, false, null, gpa);
                                                           ^
/home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib/std/Build/Fuzz.zig:175:45: 0x12a7d4b in rebuildTestsWorkerRunFallible (std.zig)
    const result = compile.rebuildInFuzzMode(gpa, prog_node);
                                            ^
/home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib/std/Build/Fuzz.zig:162:34: 0x12a842a in rebuildTestsWorkerRun (std.zig)
    rebuildTestsWorkerRunFallible(run, gpa, ttyconf, parent_prog_node) catch |err| {
                                 ^
/home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib/std/Thread/Pool.zig:118:39: 0x12a8619 in runFn (std.zig)
            @call(.auto, func, closure.arguments);
                                      ^
/home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib/std/Thread/Pool.zig:293:27: 0x1309290 in worker (std.zig)
            runnable.runFn(runnable, id);
                          ^
/home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib/std/Thread.zig:558:13: 0x127ea90 in callFn__anon_81866 (std.zig)
            @call(.auto, f, args);
            ^
/home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib/std/Thread.zig:1534:30: 0x1247130 in entryFn (std.zig)
                return callFn(f, self.fn_args);
                             ^
/home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib/std/os/linux/x86_64.zig:105:5: 0x111cef5 in clone (std.zig)
    asm volatile (
    ^
error: the following build command crashed:
.zig-cache/o/350485f651f1fca21b2d66830745d7a2/build /home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/zig /home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib /home/nixos/cs/sandbox/zigzag .zig-cache /home/nixos/.cache/zig --seed 0x33a82362 -Z8e97b72f40bd48a2 test --fuzz

The problem seems to be in std.Build.Step.evalZigProcess, which is called twice. The first time s.result_failed_command is null, but the second time it is populated with the following string, which seems to be the initial zig test invocation to find all fuzz tests:

/home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/zig test -ODebug -Mroot=/home/nixos/cs/sandbox/zigzag/src/main.zig --cache-dir .zig-cache --global-cache-dir /home/nixos/.cache/zig --name test --zig-lib-dir /home/nixos/installed/zig-x86_64-linux-0.16.0-dev.1234+74900e938/lib/ --listen=-

Expected Behavior

The fuzz test runner should not crash.

[mrdimidium]

I am facing this error on x86_64-linux-0.16.0-dev.1316+181b25ce4 with any attempts to run the fuzzer.

Playback:

cd $(mktemp -d)
zig init
zig build test --fuzz

[davnavr]

@mrdimidium By any chance, have you observed any mysterious "Failed command" messages? My build script runs system commands, and it prints that even when the commands succeed.

[mrdimidium]

@davnavr Sorry, I'm not sure I understand your question. I see the same error as in your message on an empty project, and I don't think it's related to what you're doing in your build.

[gooncreeper]

Your main.zig and build.zig are the same; however, I strongly suspect this issue was fixed by #25981