translate-c build step causing crash in build system

[andrewrk]

Zig Version

0.14.0-dev.321+888708ec8

Steps to Reproduce and Observed Behavior

Use a translate-c build step in a build script:

    const translate_c = b.addTranslateC(.{
        .root_source_file = b.path("src/c.h"),
        .target = target,
        .optimize = optimize,
    });
    exe.root_module.addImport("c", translate_c.createModule());

thread 160006 panic: index out of bounds: index 0, len 0
/home/andy/local/lib/zig/std/Build/Step.zig:551:103: 0x1211890 in zigProcessUpdate (build)
                    const prefix_index: std.zig.Server.Message.PathPrefix = @enumFromInt(prefixed_path[0] - 1);
                                                                                                      ^
/home/andy/local/lib/zig/std/Build/Step.zig:441:40: 0x1214fb0 in evalZigProcess (build)
    const result = try zigProcessUpdate(s, zp, watch);
                                       ^
/home/andy/local/lib/zig/std/Build/Step/TranslateC.zig:158:48: 0x11c8cc5 in make (build)
    const output_path = try step.evalZigProcess(argv_list.items, prog_node, false);
                                               ^
/home/andy/local/lib/zig/std/Build/Step.zig:231:13: 0x117ae67 in make (build)
    s.makeFn(s, options) catch |err| switch (err) {
            ^
/home/andy/local/lib/zig/compiler/build_runner.zig:1046:31: 0x112bacc in workerMakeOneStep (build)
    const make_result = s.make(.{
                              ^
/home/andy/local/lib/zig/std/Thread/Pool.zig:115:39: 0x112c461 in runFn (build)
            @call(.auto, func, closure.arguments);
                                      ^
/home/andy/local/lib/zig/std/Thread/Pool.zig:291:32: 0x11ac0b5 in worker (build)
            run_node.data.runFn(&run_node.data, id);
                               ^
/home/andy/local/lib/zig/std/Thread.zig:409:13: 0x1179b7d in callFn__anon_15720 (build)
            @call(.auto, f, args);
            ^
/home/andy/local/lib/zig/std/Thread.zig:1234:30: 0x112b197 in entryFn (build)
                return callFn(f, self.fn_args);
                             ^
/home/andy/dev/zig/lib/c.zig:239:13: 0x131eff0 in clone (c)
            asm volatile (
            ^

Expected Behavior

No crash.

---

Regression caused by #20580

Related to #20630

The panic happens because the frontend fails to report file system inputs in the translate-c logic. This is a bug in the frontend, not the build system.

Should be an easy fix, just need to send a non-empty file_system_inputs message here:

zig/src/main.zig

Line 4089 in 888708e

try server.serveStringMessage(.file_system_inputs, file_system_inputs.items);

[der-teufel-programming]

Could you share the whole build script and the command you run that crashes? I have trouble getting the crash locally

[andrewrk]

https://github.com/andrewrk/tetris/tree/no-cimport

zig build