evalZigProcess

pub fn evalZigProcess(
    s: *Step,
    argv: []const []const u8,
    prog_node: std.Progress.Node,
    watch: bool,
    web_server: ?*Build.WebServer,
    gpa: Allocator,
) !?Path {
    if (s.getZigProcess()) |zp| update: {
        assert(watch);
        if (std.Progress.have_ipc) if (zp.progress_ipc_fd) |fd| prog_node.setIpcFd(fd);
        const result = zigProcessUpdate(s, zp, watch, web_server, gpa) catch |err| switch (err) {
            error.BrokenPipe => {
                // Process restart required.
                const term = zp.child.wait() catch |e| {
                    return s.fail("unable to wait for {s}: {s}", .{ argv[0], @errorName(e) });
                };
                _ = term;
                s.clearZigProcess(gpa);
                break :update;
            },
            else => |e| return e,
        };

        if (s.result_error_bundle.errorMessageCount() > 0)
            return s.fail("{d} compilation errors", .{s.result_error_bundle.errorMessageCount()});

        if (s.result_error_msgs.items.len > 0 and result == null) {
            // Crash detected.
            const term = zp.child.wait() catch |e| {
                return s.fail("unable to wait for {s}: {s}", .{ argv[0], @errorName(e) });
            };
            s.result_peak_rss = zp.child.resource_usage_statistics.getMaxRss() orelse 0;
            s.clearZigProcess(gpa);
            try handleChildProcessTerm(s, term, null, argv);
            return error.MakeFailed;
        }

        return result;
    }
    assert(argv.len != 0);
    const b = s.owner;
    const arena = b.allocator;

    try handleChildProcUnsupported(s, null, argv);
    try handleVerbose(s.owner, null, argv);

    var child = std.process.Child.init(argv, arena);
    child.env_map = &b.graph.env_map;
    child.stdin_behavior = .Pipe;
    child.stdout_behavior = .Pipe;
    child.stderr_behavior = .Pipe;
    child.request_resource_usage_statistics = true;
    child.progress_node = prog_node;

    child.spawn() catch |err| return s.fail("failed to spawn zig compiler {s}: {s}", .{
        argv[0], @errorName(err),
    });

    const zp = try gpa.create(ZigProcess);
    zp.* = .{
        .child = child,
        .poller = std.Io.poll(gpa, ZigProcess.StreamEnum, .{
            .stdout = child.stdout.?,
            .stderr = child.stderr.?,
        }),
        .progress_ipc_fd = if (std.Progress.have_ipc) child.progress_node.getIpcFd() else {},
    };
    if (watch) s.setZigProcess(zp);
    defer if (!watch) {
        zp.poller.deinit();
        gpa.destroy(zp);
    };

    const result = try zigProcessUpdate(s, zp, watch, web_server, gpa);

    if (!watch) {
        // Send EOF to stdin.
        zp.child.stdin.?.close();
        zp.child.stdin = null;

        const term = zp.child.wait() catch |err| {
            return s.fail("unable to wait for {s}: {s}", .{ argv[0], @errorName(err) });
        };
        s.result_peak_rss = zp.child.resource_usage_statistics.getMaxRss() orelse 0;

        // Special handling for Compile step that is expecting compile errors.
        if (s.cast(Compile)) |compile| switch (term) {
            .Exited => {
                // Note that the exit code may be 0 in this case due to the
                // compiler server protocol.
                if (compile.expect_errors != null) {
                    return error.NeedCompileErrorCheck;
                }
            },
            else => {},
        };

        try handleChildProcessTerm(s, term, null, argv);
    }

    // This is intentionally printed for failure on the first build but not for
    // subsequent rebuilds.
    if (s.result_error_bundle.errorMessageCount() > 0) {
        return s.fail("the following command failed with {d} compilation errors:\n{s}", .{
            s.result_error_bundle.errorMessageCount(),
            try allocPrintCmd(arena, null, argv),
        });
    }

    return result;
}