const std = @import("std");
const builtin = @import("builtin");
const Step = std.Build.Step;
const fs = std.fs;
const mem = std.mem;
const process = std.process;
const ArrayList = std.ArrayList;
const EnvMap = process.EnvMap;
const Allocator = mem.Allocator;
const ExecError = std.Build.ExecError;
const assert = std.debug.assert;

const Run = @This();

pub const base_id: Step.Id = .run;

step: Step,

/// See also addArg and addArgs to modifying this directly
argv: ArrayList(Arg),

/// Set this to modify the current working directory
/// TODO change this to a Build.Cache.Directory to better integrate with
/// future child process cwd API.
cwd: ?[]const u8,

/// Override this field to modify the environment, or use setEnvironmentVariable
env_map: ?*EnvMap,

/// Configures whether the Run step is considered to have side-effects, and also
/// whether the Run step will inherit stdio streams, forwarding them to the
/// parent process, in which case will require a global lock to prevent other
/// steps from interfering with stdio while the subprocess associated with this
/// Run step is running.
/// If the Run step is determined to not have side-effects, then execution will
/// be skipped if all output files are up-to-date and input files are
/// unchanged.
stdio: StdIo = .infer_from_args,
/// This field must be `null` if stdio is `inherit`.
stdin: ?[]const u8 = null,

/// Additional file paths relative to build.zig that, when modified, indicate
/// that the Run step should be re-executed.
/// If the Run step is determined to have side-effects, this field is ignored
/// and the Run step is always executed when it appears in the build graph.
extra_file_dependencies: []const []const u8 = &.{},

/// After adding an output argument, this step will by default rename itself
/// for a better display name in the build summary.
/// This can be disabled by setting this to false.
rename_step_with_output_arg: bool = true,

/// If this is true, a Run step which is configured to check the output of the
/// executed binary will not fail the build if the binary cannot be executed
/// due to being for a foreign binary to the host system which is running the
/// build graph.
/// Command-line arguments such as -fqemu and -fwasmtime may affect whether a
/// binary is detected as foreign, as well as system configuration such as
/// Rosetta (macOS) and binfmt_misc (Linux).
/// If this Run step is considered to have side-effects, then this flag does
/// nothing.
skip_foreign_checks: bool = false,

/// If stderr or stdout exceeds this amount, the child process is killed and
/// the step fails.
max_stdio_size: usize = 10 * 1024 * 1024,

captured_stdout: ?*Output = null,
captured_stderr: ?*Output = null,

has_side_effects: bool = false,

pub const StdIo = union(enum) {
    /// Whether the Run step has side-effects will be determined by whether or not one
    /// of the args is an output file (added with `addOutputFileArg`).
    /// If the Run step is determined to have side-effects, this is the same as `inherit`.
    /// The step will fail if the subprocess crashes or returns a non-zero exit code.
    infer_from_args,
    /// Causes the Run step to be considered to have side-effects, and therefore
    /// always execute when it appears in the build graph.
    /// It also means that this step will obtain a global lock to prevent other
    /// steps from running in the meantime.
    /// The step will fail if the subprocess crashes or returns a non-zero exit code.
    inherit,
    /// Causes the Run step to be considered to *not* have side-effects. The
    /// process will be re-executed if any of the input dependencies are
    /// modified. The exit code and standard I/O streams will be checked for
    /// certain conditions, and the step will succeed or fail based on these
    /// conditions.
    /// Note that an explicit check for exit code 0 needs to be added to this
    /// list if such a check is desirable.
    check: std.ArrayList(Check),
    /// This Run step is running a zig unit test binary and will communicate
    /// extra metadata over the IPC protocol.
    zig_test,

    pub const Check = union(enum) {
        expect_stderr_exact: []const u8,
        expect_stderr_match: []const u8,
        expect_stdout_exact: []const u8,
        expect_stdout_match: []const u8,
        expect_term: std.process.Child.Term,
    };
};

pub const Arg = union(enum) {
    artifact: *Step.Compile,
    file_source: std.Build.FileSource,
    directory_source: std.Build.FileSource,
    bytes: []u8,
    output: *Output,
};

pub const Output = struct {
    generated_file: std.Build.GeneratedFile,
    prefix: []const u8,
    basename: []const u8,
};

pub fn create(owner: *std.Build, name: []const u8) *Run {
    const self = owner.allocator.create(Run) catch @panic("OOM");
    self.* = .{
        .step = Step.init(.{
            .id = base_id,
            .name = name,
            .owner = owner,
            .makeFn = make,
        }),
        .argv = ArrayList(Arg).init(owner.allocator),
        .cwd = null,
        .env_map = null,
    };
    return self;
}

pub fn setName(self: *Run, name: []const u8) void {
    self.step.name = name;
    self.rename_step_with_output_arg = false;
}

pub fn enableTestRunnerMode(rs: *Run) void {
    rs.stdio = .zig_test;
    rs.addArgs(&.{"--listen=-"});
}

pub fn addArtifactArg(self: *Run, artifact: *Step.Compile) void {
    self.argv.append(Arg{ .artifact = artifact }) catch @panic("OOM");
    self.step.dependOn(&artifact.step);
}

/// This provides file path as a command line argument to the command being
/// run, and returns a FileSource which can be used as inputs to other APIs
/// throughout the build system.
pub fn addOutputFileArg(rs: *Run, basename: []const u8) std.Build.FileSource {
    return addPrefixedOutputFileArg(rs, "", basename);
}

pub fn addPrefixedOutputFileArg(
    rs: *Run,
    prefix: []const u8,
    basename: []const u8,
) std.Build.FileSource {
    const b = rs.step.owner;

    const output = b.allocator.create(Output) catch @panic("OOM");
    output.* = .{
        .prefix = prefix,
        .basename = basename,
        .generated_file = .{ .step = &rs.step },
    };
    rs.argv.append(.{ .output = output }) catch @panic("OOM");

    if (rs.rename_step_with_output_arg) {
        rs.setName(b.fmt("{s} ({s})", .{ rs.step.name, basename }));
    }

    return .{ .generated = &output.generated_file };
}

pub fn addFileSourceArg(self: *Run, file_source: std.Build.FileSource) void {
    self.argv.append(.{
        .file_source = file_source.dupe(self.step.owner),
    }) catch @panic("OOM");
    file_source.addStepDependencies(&self.step);
}

pub fn addDirectorySourceArg(self: *Run, directory_source: std.Build.FileSource) void {
    self.argv.append(.{
        .directory_source = directory_source.dupe(self.step.owner),
    }) catch @panic("OOM");
    directory_source.addStepDependencies(&self.step);
}

pub fn addArg(self: *Run, arg: []const u8) void {
    self.argv.append(.{ .bytes = self.step.owner.dupe(arg) }) catch @panic("OOM");
}

pub fn addArgs(self: *Run, args: []const []const u8) void {
    for (args) |arg| {
        self.addArg(arg);
    }
}

pub fn clearEnvironment(self: *Run) void {
    const b = self.step.owner;
    const new_env_map = b.allocator.create(EnvMap) catch @panic("OOM");
    new_env_map.* = EnvMap.init(b.allocator);
    self.env_map = new_env_map;
}

pub fn addPathDir(self: *Run, search_path: []const u8) void {
    const b = self.step.owner;
    const env_map = getEnvMapInternal(self);

    const key = "PATH";
    var prev_path = env_map.get(key);

    if (prev_path) |pp| {
        const new_path = b.fmt("{s}" ++ [1]u8{fs.path.delimiter} ++ "{s}", .{ pp, search_path });
        env_map.put(key, new_path) catch @panic("OOM");
    } else {
        env_map.put(key, b.dupePath(search_path)) catch @panic("OOM");
    }
}

pub fn getEnvMap(self: *Run) *EnvMap {
    return getEnvMapInternal(self);
}

fn getEnvMapInternal(self: *Run) *EnvMap {
    const arena = self.step.owner.allocator;
    return self.env_map orelse {
        const env_map = arena.create(EnvMap) catch @panic("OOM");
        env_map.* = process.getEnvMap(arena) catch @panic("unhandled error");
        self.env_map = env_map;
        return env_map;
    };
}

pub fn setEnvironmentVariable(self: *Run, key: []const u8, value: []const u8) void {
    const b = self.step.owner;
    const env_map = self.getEnvMap();
    env_map.put(b.dupe(key), b.dupe(value)) catch @panic("unhandled error");
}

pub fn removeEnvironmentVariable(self: *Run, key: []const u8) void {
    self.getEnvMap().remove(key);
}

/// Adds a check for exact stderr match. Does not add any other checks.
pub fn expectStdErrEqual(self: *Run, bytes: []const u8) void {
    const new_check: StdIo.Check = .{ .expect_stderr_exact = self.step.owner.dupe(bytes) };
    self.addCheck(new_check);
}

/// Adds a check for exact stdout match as well as a check for exit code 0, if
/// there is not already an expected termination check.
pub fn expectStdOutEqual(self: *Run, bytes: []const u8) void {
    const new_check: StdIo.Check = .{ .expect_stdout_exact = self.step.owner.dupe(bytes) };
    self.addCheck(new_check);
    if (!self.hasTermCheck()) {
        self.expectExitCode(0);
    }
}

pub fn expectExitCode(self: *Run, code: u8) void {
    const new_check: StdIo.Check = .{ .expect_term = .{ .Exited = code } };
    self.addCheck(new_check);
}

pub fn hasTermCheck(self: Run) bool {
    for (self.stdio.check.items) |check| switch (check) {
        .expect_term => return true,
        else => continue,
    };
    return false;
}

pub fn addCheck(self: *Run, new_check: StdIo.Check) void {
    switch (self.stdio) {
        .infer_from_args => {
            self.stdio = .{ .check = std.ArrayList(StdIo.Check).init(self.step.owner.allocator) };
            self.stdio.check.append(new_check) catch @panic("OOM");
        },
        .check => |*checks| checks.append(new_check) catch @panic("OOM"),
        else => @panic("illegal call to addCheck: conflicting helper method calls. Suggest to directly set stdio field of Run instead"),
    }
}

pub fn captureStdErr(self: *Run) std.Build.FileSource {
    assert(self.stdio != .inherit);

    if (self.captured_stderr) |output| return .{ .generated = &output.generated_file };

    const output = self.step.owner.allocator.create(Output) catch @panic("OOM");
    output.* = .{
        .prefix = "",
        .basename = "stderr",
        .generated_file = .{ .step = &self.step },
    };
    self.captured_stderr = output;
    return .{ .generated = &output.generated_file };
}

pub fn captureStdOut(self: *Run) std.Build.FileSource {
    assert(self.stdio != .inherit);

    if (self.captured_stdout) |output| return .{ .generated = &output.generated_file };

    const output = self.step.owner.allocator.create(Output) catch @panic("OOM");
    output.* = .{
        .prefix = "",
        .basename = "stdout",
        .generated_file = .{ .step = &self.step },
    };
    self.captured_stdout = output;
    return .{ .generated = &output.generated_file };
}

/// Returns whether the Run step has side effects *other than* updating the output arguments.
fn hasSideEffects(self: Run) bool {
    if (self.has_side_effects) return true;
    return switch (self.stdio) {
        .infer_from_args => !self.hasAnyOutputArgs(),
        .inherit => true,
        .check => false,
        .zig_test => false,
    };
}

fn hasAnyOutputArgs(self: Run) bool {
    if (self.captured_stdout != null) return true;
    if (self.captured_stderr != null) return true;
    for (self.argv.items) |arg| switch (arg) {
        .output => return true,
        else => continue,
    };
    return false;
}

fn checksContainStdout(checks: []const StdIo.Check) bool {
    for (checks) |check| switch (check) {
        .expect_stderr_exact,
        .expect_stderr_match,
        .expect_term,
        => continue,

        .expect_stdout_exact,
        .expect_stdout_match,
        => return true,
    };
    return false;
}

fn checksContainStderr(checks: []const StdIo.Check) bool {
    for (checks) |check| switch (check) {
        .expect_stdout_exact,
        .expect_stdout_match,
        .expect_term,
        => continue,

        .expect_stderr_exact,
        .expect_stderr_match,
        => return true,
    };
    return false;
}

fn make(step: *Step, prog_node: *std.Progress.Node) !void {
    const b = step.owner;
    const arena = b.allocator;
    const self = @fieldParentPtr(Run, "step", step);
    const has_side_effects = self.hasSideEffects();

    var argv_list = ArrayList([]const u8).init(arena);
    var output_placeholders = ArrayList(struct {
        index: usize,
        output: *Output,
    }).init(arena);

    var man = b.cache.obtain();
    defer man.deinit();

    for (self.argv.items) |arg| {
        switch (arg) {
            .bytes => |bytes| {
                try argv_list.append(bytes);
                man.hash.addBytes(bytes);
            },
            .file_source => |file| {
                const file_path = file.getPath(b);
                try argv_list.append(file_path);
                _ = try man.addFile(file_path, null);
            },
            .directory_source => |file| {
                const file_path = file.getPath(b);
                try argv_list.append(file_path);
                man.hash.addBytes(file_path);
            },
            .artifact => |artifact| {
                if (artifact.target.isWindows()) {
                    // On Windows we don't have rpaths so we have to add .dll search paths to PATH
                    self.addPathForDynLibs(artifact);
                }
                const file_path = artifact.installed_path orelse
                    artifact.getOutputSource().getPath(b);

                try argv_list.append(file_path);

                _ = try man.addFile(file_path, null);
            },
            .output => |output| {
                man.hash.addBytes(output.prefix);
                man.hash.addBytes(output.basename);
                // Add a placeholder into the argument list because we need the
                // manifest hash to be updated with all arguments before the
                // object directory is computed.
                try argv_list.append("");
                try output_placeholders.append(.{
                    .index = argv_list.items.len - 1,
                    .output = output,
                });
            },
        }
    }

    if (self.captured_stdout) |output| {
        man.hash.addBytes(output.basename);
    }

    if (self.captured_stderr) |output| {
        man.hash.addBytes(output.basename);
    }

    hashStdIo(&man.hash, self.stdio);

    if (has_side_effects) {
        try runCommand(self, argv_list.items, has_side_effects, null, prog_node);
        return;
    }

    for (self.extra_file_dependencies) |file_path| {
        _ = try man.addFile(b.pathFromRoot(file_path), null);
    }

    if (try step.cacheHit(&man)) {
        // cache hit, skip running command
        const digest = man.final();
        for (output_placeholders.items) |placeholder| {
            placeholder.output.generated_file.path = try b.cache_root.join(arena, &.{
                "o", &digest, placeholder.output.basename,
            });
        }

        if (self.captured_stdout) |output| {
            output.generated_file.path = try b.cache_root.join(arena, &.{
                "o", &digest, output.basename,
            });
        }

        if (self.captured_stderr) |output| {
            output.generated_file.path = try b.cache_root.join(arena, &.{
                "o", &digest, output.basename,
            });
        }

        step.result_cached = true;
        return;
    }

    const digest = man.final();

    for (output_placeholders.items) |placeholder| {
        const output_components = .{ "o", &digest, placeholder.output.basename };
        const output_sub_path = try fs.path.join(arena, &output_components);
        const output_sub_dir_path = fs.path.dirname(output_sub_path).?;
        b.cache_root.handle.makePath(output_sub_dir_path) catch |err| {
            return step.fail("unable to make path '{}{s}': {s}", .{
                b.cache_root, output_sub_dir_path, @errorName(err),
            });
        };
        const output_path = try b.cache_root.join(arena, &output_components);
        placeholder.output.generated_file.path = output_path;
        const cli_arg = if (placeholder.output.prefix.len == 0)
            output_path
        else
            b.fmt("{s}{s}", .{ placeholder.output.prefix, output_path });
        argv_list.items[placeholder.index] = cli_arg;
    }

    try runCommand(self, argv_list.items, has_side_effects, &digest, prog_node);

    try step.writeManifest(&man);
}

fn formatTerm(
    term: ?std.process.Child.Term,
    comptime fmt: []const u8,
    options: std.fmt.FormatOptions,
    writer: anytype,
) !void {
    _ = fmt;
    _ = options;
    if (term) |t| switch (t) {
        .Exited => |code| try writer.print("exited with code {}", .{code}),
        .Signal => |sig| try writer.print("terminated with signal {}", .{sig}),
        .Stopped => |sig| try writer.print("stopped with signal {}", .{sig}),
        .Unknown => |code| try writer.print("terminated for unknown reason with code {}", .{code}),
    } else {
        try writer.writeAll("exited with any code");
    }
}
fn fmtTerm(term: ?std.process.Child.Term) std.fmt.Formatter(formatTerm) {
    return .{ .data = term };
}

fn termMatches(expected: ?std.process.Child.Term, actual: std.process.Child.Term) bool {
    return if (expected) |e| switch (e) {
        .Exited => |expected_code| switch (actual) {
            .Exited => |actual_code| expected_code == actual_code,
            else => false,
        },
        .Signal => |expected_sig| switch (actual) {
            .Signal => |actual_sig| expected_sig == actual_sig,
            else => false,
        },
        .Stopped => |expected_sig| switch (actual) {
            .Stopped => |actual_sig| expected_sig == actual_sig,
            else => false,
        },
        .Unknown => |expected_code| switch (actual) {
            .Unknown => |actual_code| expected_code == actual_code,
            else => false,
        },
    } else switch (actual) {
        .Exited => true,
        else => false,
    };
}

fn runCommand(
    self: *Run,
    argv: []const []const u8,
    has_side_effects: bool,
    digest: ?*const [std.Build.Cache.hex_digest_len]u8,
    prog_node: *std.Progress.Node,
) !void {
    const step = &self.step;
    const b = step.owner;
    const arena = b.allocator;

    try step.handleChildProcUnsupported(self.cwd, argv);
    try Step.handleVerbose2(step.owner, self.cwd, self.env_map, argv);

    const allow_skip = switch (self.stdio) {
        .check, .zig_test => self.skip_foreign_checks,
        else => false,
    };

    var interp_argv = std.ArrayList([]const u8).init(b.allocator);
    defer interp_argv.deinit();

    const result = spawnChildAndCollect(self, argv, has_side_effects, prog_node) catch |err| term: {
        // InvalidExe: cpu arch mismatch
        // FileNotFound: can happen with a wrong dynamic linker path
        if (err == error.InvalidExe or err == error.FileNotFound) interpret: {
            // TODO: learn the target from the binary directly rather than from
            // relying on it being a Compile step. This will make this logic
            // work even for the edge case that the binary was produced by a
            // third party.
            const exe = switch (self.argv.items[0]) {
                .artifact => |exe| exe,
                else => break :interpret,
            };
            switch (exe.kind) {
                .exe, .@"test" => {},
                else => break :interpret,
            }

            const need_cross_glibc = exe.target.isGnuLibC() and exe.is_linking_libc;
            switch (b.host.getExternalExecutor(exe.target_info, .{
                .qemu_fixes_dl = need_cross_glibc and b.glibc_runtimes_dir != null,
                .link_libc = exe.is_linking_libc,
            })) {
                .native, .rosetta => {
                    if (allow_skip) return error.MakeSkipped;
                    break :interpret;
                },
                .wine => |bin_name| {
                    if (b.enable_wine) {
                        try interp_argv.append(bin_name);
                        try interp_argv.appendSlice(argv);
                    } else {
                        return failForeign(self, "-fwine", argv[0], exe);
                    }
                },
                .qemu => |bin_name| {
                    if (b.enable_qemu) {
                        const glibc_dir_arg = if (need_cross_glibc)
                            b.glibc_runtimes_dir orelse
                                return failForeign(self, "--glibc-runtimes", argv[0], exe)
                        else
                            null;

                        try interp_argv.append(bin_name);

                        if (glibc_dir_arg) |dir| {
                            // TODO look into making this a call to `linuxTriple`. This
                            // needs the directory to be called "i686" rather than
                            // "x86" which is why we do it manually here.
                            const fmt_str = "{s}" ++ fs.path.sep_str ++ "{s}-{s}-{s}";
                            const cpu_arch = exe.target.getCpuArch();
                            const os_tag = exe.target.getOsTag();
                            const abi = exe.target.getAbi();
                            const cpu_arch_name: []const u8 = if (cpu_arch == .x86)
                                "i686"
                            else
                                @tagName(cpu_arch);
                            const full_dir = try std.fmt.allocPrint(b.allocator, fmt_str, .{
                                dir, cpu_arch_name, @tagName(os_tag), @tagName(abi),
                            });

                            try interp_argv.append("-L");
                            try interp_argv.append(full_dir);
                        }

                        try interp_argv.appendSlice(argv);
                    } else {
                        return failForeign(self, "-fqemu", argv[0], exe);
                    }
                },
                .darling => |bin_name| {
                    if (b.enable_darling) {
                        try interp_argv.append(bin_name);
                        try interp_argv.appendSlice(argv);
                    } else {
                        return failForeign(self, "-fdarling", argv[0], exe);
                    }
                },
                .wasmtime => |bin_name| {
                    if (b.enable_wasmtime) {
                        try interp_argv.append(bin_name);
                        try interp_argv.append("--dir=.");
                        try interp_argv.append(argv[0]);
                        try interp_argv.append("--");
                        try interp_argv.appendSlice(argv[1..]);
                    } else {
                        return failForeign(self, "-fwasmtime", argv[0], exe);
                    }
                },
                .bad_dl => |foreign_dl| {
                    if (allow_skip) return error.MakeSkipped;

                    const host_dl = b.host.dynamic_linker.get() orelse "(none)";

                    return step.fail(
                        \\the host system is unable to execute binaries from the target
                        \\  because the host dynamic linker is '{s}',
                        \\  while the target dynamic linker is '{s}'.
                        \\  consider setting the dynamic linker or enabling skip_foreign_checks in the Run step
                    , .{ host_dl, foreign_dl });
                },
                .bad_os_or_cpu => {
                    if (allow_skip) return error.MakeSkipped;

                    const host_name = try b.host.target.zigTriple(b.allocator);
                    const foreign_name = try exe.target.zigTriple(b.allocator);

                    return step.fail("the host system ({s}) is unable to execute binaries from the target ({s})", .{
                        host_name, foreign_name,
                    });
                },
            }

            if (exe.target.isWindows()) {
                // On Windows we don't have rpaths so we have to add .dll search paths to PATH
                self.addPathForDynLibs(exe);
            }

            try Step.handleVerbose2(step.owner, self.cwd, self.env_map, interp_argv.items);

            break :term spawnChildAndCollect(self, interp_argv.items, has_side_effects, prog_node) catch |e| {
                return step.fail("unable to spawn interpreter {s}: {s}", .{
                    interp_argv.items[0], @errorName(e),
                });
            };
        }

        return step.fail("unable to spawn {s}: {s}", .{ argv[0], @errorName(err) });
    };

    step.result_duration_ns = result.elapsed_ns;
    step.result_peak_rss = result.peak_rss;
    step.test_results = result.stdio.test_results;

    // Capture stdout and stderr to GeneratedFile objects.
    const Stream = struct {
        captured: ?*Output,
        is_null: bool,
        bytes: []const u8,
    };
    for ([_]Stream{
        .{
            .captured = self.captured_stdout,
            .is_null = result.stdio.stdout_null,
            .bytes = result.stdio.stdout,
        },
        .{
            .captured = self.captured_stderr,
            .is_null = result.stdio.stderr_null,
            .bytes = result.stdio.stderr,
        },
    }) |stream| {
        if (stream.captured) |output| {
            assert(!stream.is_null);

            const output_components = .{ "o", digest.?, output.basename };
            const output_path = try b.cache_root.join(arena, &output_components);
            output.generated_file.path = output_path;

            const sub_path = try fs.path.join(arena, &output_components);
            const sub_path_dirname = fs.path.dirname(sub_path).?;
            b.cache_root.handle.makePath(sub_path_dirname) catch |err| {
                return step.fail("unable to make path '{}{s}': {s}", .{
                    b.cache_root, sub_path_dirname, @errorName(err),
                });
            };
            b.cache_root.handle.writeFile(sub_path, stream.bytes) catch |err| {
                return step.fail("unable to write file '{}{s}': {s}", .{
                    b.cache_root, sub_path, @errorName(err),
                });
            };
        }
    }

    const final_argv = if (interp_argv.items.len == 0) argv else interp_argv.items;

    switch (self.stdio) {
        .check => |checks| for (checks.items) |check| switch (check) {
            .expect_stderr_exact => |expected_bytes| {
                assert(!result.stdio.stderr_null);
                if (!mem.eql(u8, expected_bytes, result.stdio.stderr)) {
                    return step.fail(
                        \\
                        \\========= expected this stderr: =========
                        \\{s}
                        \\========= but found: ====================
                        \\{s}
                        \\========= from the following command: ===
                        \\{s}
                    , .{
                        expected_bytes,
                        result.stdio.stderr,
                        try Step.allocPrintCmd(arena, self.cwd, final_argv),
                    });
                }
            },
            .expect_stderr_match => |match| {
                assert(!result.stdio.stderr_null);
                if (mem.indexOf(u8, result.stdio.stderr, match) == null) {
                    return step.fail(
                        \\
                        \\========= expected to find in stderr: =========
                        \\{s}
                        \\========= but stderr does not contain it: =====
                        \\{s}
                        \\========= from the following command: =========
                        \\{s}
                    , .{
                        match,
                        result.stdio.stderr,
                        try Step.allocPrintCmd(arena, self.cwd, final_argv),
                    });
                }
            },
            .expect_stdout_exact => |expected_bytes| {
                assert(!result.stdio.stdout_null);
                if (!mem.eql(u8, expected_bytes, result.stdio.stdout)) {
                    return step.fail(
                        \\
                        \\========= expected this stdout: =========
                        \\{s}
                        \\========= but found: ====================
                        \\{s}
                        \\========= from the following command: ===
                        \\{s}
                    , .{
                        expected_bytes,
                        result.stdio.stdout,
                        try Step.allocPrintCmd(arena, self.cwd, final_argv),
                    });
                }
            },
            .expect_stdout_match => |match| {
                assert(!result.stdio.stdout_null);
                if (mem.indexOf(u8, result.stdio.stdout, match) == null) {
                    return step.fail(
                        \\
                        \\========= expected to find in stdout: =========
                        \\{s}
                        \\========= but stdout does not contain it: =====
                        \\{s}
                        \\========= from the following command: =========
                        \\{s}
                    , .{
                        match,
                        result.stdio.stdout,
                        try Step.allocPrintCmd(arena, self.cwd, final_argv),
                    });
                }
            },
            .expect_term => |expected_term| {
                if (!termMatches(expected_term, result.term)) {
                    return step.fail("the following command {} (expected {}):\n{s}", .{
                        fmtTerm(result.term),
                        fmtTerm(expected_term),
                        try Step.allocPrintCmd(arena, self.cwd, final_argv),
                    });
                }
            },
        },
        .zig_test => {
            const prefix: []const u8 = p: {
                if (result.stdio.test_metadata) |tm| {
                    if (tm.next_index > 0 and tm.next_index <= tm.names.len) {
                        const name = tm.testName(tm.next_index - 1);
                        break :p b.fmt("while executing test '{s}', ", .{name});
                    }
                }
                break :p "";
            };
            const expected_term: std.process.Child.Term = .{ .Exited = 0 };
            if (!termMatches(expected_term, result.term)) {
                return step.fail("{s}the following command {} (expected {}):\n{s}", .{
                    prefix,
                    fmtTerm(result.term),
                    fmtTerm(expected_term),
                    try Step.allocPrintCmd(arena, self.cwd, final_argv),
                });
            }
            if (!result.stdio.test_results.isSuccess()) {
                return step.fail(
                    "{s}the following test command failed:\n{s}",
                    .{ prefix, try Step.allocPrintCmd(arena, self.cwd, final_argv) },
                );
            }
        },
        else => {
            try step.handleChildProcessTerm(result.term, self.cwd, final_argv);
        },
    }
}

const ChildProcResult = struct {
    term: std.process.Child.Term,
    elapsed_ns: u64,
    peak_rss: usize,

    stdio: StdIoResult,
};

fn spawnChildAndCollect(
    self: *Run,
    argv: []const []const u8,
    has_side_effects: bool,
    prog_node: *std.Progress.Node,
) !ChildProcResult {
    const b = self.step.owner;
    const arena = b.allocator;

    var child = std.process.Child.init(argv, arena);
    if (self.cwd) |cwd| {
        child.cwd = b.pathFromRoot(cwd);
    } else {
        child.cwd = b.build_root.path;
        child.cwd_dir = b.build_root.handle;
    }
    child.env_map = self.env_map orelse b.env_map;
    child.request_resource_usage_statistics = true;

    child.stdin_behavior = switch (self.stdio) {
        .infer_from_args => if (has_side_effects) .Inherit else .Ignore,
        .inherit => .Inherit,
        .check => .Ignore,
        .zig_test => .Pipe,
    };
    child.stdout_behavior = switch (self.stdio) {
        .infer_from_args => if (has_side_effects) .Inherit else .Ignore,
        .inherit => .Inherit,
        .check => |checks| if (checksContainStdout(checks.items)) .Pipe else .Ignore,
        .zig_test => .Pipe,
    };
    child.stderr_behavior = switch (self.stdio) {
        .infer_from_args => if (has_side_effects) .Inherit else .Pipe,
        .inherit => .Inherit,
        .check => .Pipe,
        .zig_test => .Pipe,
    };
    if (self.captured_stdout != null) child.stdout_behavior = .Pipe;
    if (self.captured_stderr != null) child.stderr_behavior = .Pipe;
    if (self.stdin != null) {
        assert(child.stdin_behavior != .Inherit);
        child.stdin_behavior = .Pipe;
    }

    try child.spawn();
    var timer = try std.time.Timer.start();

    const result = if (self.stdio == .zig_test)
        evalZigTest(self, &child, prog_node)
    else
        evalGeneric(self, &child);

    const term = try child.wait();
    const elapsed_ns = timer.read();

    return .{
        .stdio = try result,
        .term = term,
        .elapsed_ns = elapsed_ns,
        .peak_rss = child.resource_usage_statistics.getMaxRss() orelse 0,
    };
}

const StdIoResult = struct {
    // These use boolean flags instead of optionals as a workaround for
    // https://github.com/ziglang/zig/issues/14783
    stdout: []const u8,
    stderr: []const u8,
    stdout_null: bool,
    stderr_null: bool,
    test_results: Step.TestResults,
    test_metadata: ?TestMetadata,
};

fn evalZigTest(
    self: *Run,
    child: *std.process.Child,
    prog_node: *std.Progress.Node,
) !StdIoResult {
    const gpa = self.step.owner.allocator;
    const arena = self.step.owner.allocator;

    var poller = std.io.poll(gpa, enum { stdout, stderr }, .{
        .stdout = child.stdout.?,
        .stderr = child.stderr.?,
    });
    defer poller.deinit();

    try sendMessage(child.stdin.?, .query_test_metadata);

    const Header = std.zig.Server.Message.Header;

    const stdout = poller.fifo(.stdout);
    const stderr = poller.fifo(.stderr);

    var fail_count: u32 = 0;
    var skip_count: u32 = 0;
    var leak_count: u32 = 0;
    var test_count: u32 = 0;

    var metadata: ?TestMetadata = null;

    var sub_prog_node: ?std.Progress.Node = null;
    defer if (sub_prog_node) |*n| n.end();

    poll: while (true) {
        while (stdout.readableLength() < @sizeOf(Header)) {
            if (!(try poller.poll())) break :poll;
        }
        const header = stdout.reader().readStruct(Header) catch unreachable;
        while (stdout.readableLength() < header.bytes_len) {
            if (!(try poller.poll())) break :poll;
        }
        const body = stdout.readableSliceOfLen(header.bytes_len);

        switch (header.tag) {
            .zig_version => {
                if (!std.mem.eql(u8, builtin.zig_version_string, body)) {
                    return self.step.fail(
                        "zig version mismatch build runner vs compiler: '{s}' vs '{s}'",
                        .{ builtin.zig_version_string, body },
                    );
                }
            },
            .test_metadata => {
                const TmHdr = std.zig.Server.Message.TestMetadata;
                const tm_hdr = @ptrCast(*align(1) const TmHdr, body);
                test_count = tm_hdr.tests_len;

                const names_bytes = body[@sizeOf(TmHdr)..][0 .. test_count * @sizeOf(u32)];
                const async_frame_lens_bytes = body[@sizeOf(TmHdr) + names_bytes.len ..][0 .. test_count * @sizeOf(u32)];
                const expected_panic_msgs_bytes = body[@sizeOf(TmHdr) + names_bytes.len + async_frame_lens_bytes.len ..][0 .. test_count * @sizeOf(u32)];
                const string_bytes = body[@sizeOf(TmHdr) + names_bytes.len + async_frame_lens_bytes.len + expected_panic_msgs_bytes.len ..][0..tm_hdr.string_bytes_len];

                const names = std.mem.bytesAsSlice(u32, names_bytes);
                const async_frame_lens = std.mem.bytesAsSlice(u32, async_frame_lens_bytes);
                const expected_panic_msgs = std.mem.bytesAsSlice(u32, expected_panic_msgs_bytes);
                const names_aligned = try arena.alloc(u32, names.len);
                for (names_aligned, names) |*dest, src| dest.* = src;

                const async_frame_lens_aligned = try arena.alloc(u32, async_frame_lens.len);
                for (async_frame_lens_aligned, async_frame_lens) |*dest, src| dest.* = src;

                const expected_panic_msgs_aligned = try arena.alloc(u32, expected_panic_msgs.len);
                for (expected_panic_msgs_aligned, expected_panic_msgs) |*dest, src| dest.* = src;

                prog_node.setEstimatedTotalItems(names.len);
                metadata = .{
                    .string_bytes = try arena.dupe(u8, string_bytes),
                    .names = names_aligned,
                    .async_frame_lens = async_frame_lens_aligned,
                    .expected_panic_msgs = expected_panic_msgs_aligned,
                    .next_index = 0,
                    .prog_node = prog_node,
                };

                try requestNextTest(child.stdin.?, &metadata.?, &sub_prog_node);
            },
            .test_results => {
                const md = metadata.?;

                const TrHdr = std.zig.Server.Message.TestResults;
                const tr_hdr = @ptrCast(*align(1) const TrHdr, body);
                fail_count += @boolToInt(tr_hdr.flags.fail);
                skip_count += @boolToInt(tr_hdr.flags.skip);
                leak_count += @boolToInt(tr_hdr.flags.leak);

                if (tr_hdr.flags.fail or tr_hdr.flags.leak) {
                    const name = std.mem.sliceTo(md.string_bytes[md.names[tr_hdr.index]..], 0);
                    const msg = std.mem.trim(u8, stderr.readableSlice(0), "\n");
                    const label = if (tr_hdr.flags.fail) "failed" else "leaked";
                    if (msg.len > 0) {
                        try self.step.addError("'{s}' {s}: {s}", .{ name, label, msg });
                    } else {
                        try self.step.addError("'{s}' {s}", .{ name, label });
                    }
                    stderr.discard(msg.len);
                }

                try requestNextTest(child.stdin.?, &metadata.?, &sub_prog_node);
            },
            else => {}, // ignore other messages
        }

        stdout.discard(body.len);
    }

    if (stderr.readableLength() > 0) {
        const msg = std.mem.trim(u8, try stderr.toOwnedSlice(), "\n");
        if (msg.len > 0) try self.step.result_error_msgs.append(arena, msg);
    }

    // Send EOF to stdin.
    child.stdin.?.close();
    child.stdin = null;

    return .{
        .stdout = &.{},
        .stderr = &.{},
        .stdout_null = true,
        .stderr_null = true,
        .test_results = .{
            .test_count = test_count,
            .fail_count = fail_count,
            .skip_count = skip_count,
            .leak_count = leak_count,
        },
        .test_metadata = metadata,
    };
}

const TestMetadata = struct {
    names: []const u32,
    async_frame_lens: []const u32,
    expected_panic_msgs: []const u32,
    string_bytes: []const u8,
    next_index: u32,
    prog_node: *std.Progress.Node,

    fn testName(tm: TestMetadata, index: u32) []const u8 {
        return std.mem.sliceTo(tm.string_bytes[tm.names[index]..], 0);
    }
};

fn requestNextTest(in: fs.File, metadata: *TestMetadata, sub_prog_node: *?std.Progress.Node) !void {
    while (metadata.next_index < metadata.names.len) {
        const i = metadata.next_index;
        metadata.next_index += 1;

        if (metadata.async_frame_lens[i] != 0) continue;
        if (metadata.expected_panic_msgs[i] != 0) continue;

        const name = metadata.testName(i);
        if (sub_prog_node.*) |*n| n.end();
        sub_prog_node.* = metadata.prog_node.start(name, 0);

        try sendRunTestMessage(in, i);
        return;
    } else {
        try sendMessage(in, .exit);
    }
}

fn sendMessage(file: std.fs.File, tag: std.zig.Client.Message.Tag) !void {
    const header: std.zig.Client.Message.Header = .{
        .tag = tag,
        .bytes_len = 0,
    };
    try file.writeAll(std.mem.asBytes(&header));
}

fn sendRunTestMessage(file: std.fs.File, index: u32) !void {
    const header: std.zig.Client.Message.Header = .{
        .tag = .run_test,
        .bytes_len = 4,
    };
    const full_msg = std.mem.asBytes(&header) ++ std.mem.asBytes(&index);
    try file.writeAll(full_msg);
}

fn evalGeneric(self: *Run, child: *std.process.Child) !StdIoResult {
    const arena = self.step.owner.allocator;

    if (self.stdin) |stdin| {
        child.stdin.?.writeAll(stdin) catch |err| {
            return self.step.fail("unable to write stdin: {s}", .{@errorName(err)});
        };
        child.stdin.?.close();
        child.stdin = null;
    }

    // These are not optionals, as a workaround for
    // https://github.com/ziglang/zig/issues/14783
    var stdout_bytes: []const u8 = undefined;
    var stderr_bytes: []const u8 = undefined;
    var stdout_null = true;
    var stderr_null = true;

    if (child.stdout) |stdout| {
        if (child.stderr) |stderr| {
            var poller = std.io.poll(arena, enum { stdout, stderr }, .{
                .stdout = stdout,
                .stderr = stderr,
            });
            defer poller.deinit();

            while (try poller.poll()) {
                if (poller.fifo(.stdout).count > self.max_stdio_size)
                    return error.StdoutStreamTooLong;
                if (poller.fifo(.stderr).count > self.max_stdio_size)
                    return error.StderrStreamTooLong;
            }

            stdout_bytes = try poller.fifo(.stdout).toOwnedSlice();
            stderr_bytes = try poller.fifo(.stderr).toOwnedSlice();
            stdout_null = false;
            stderr_null = false;
        } else {
            stdout_bytes = try stdout.reader().readAllAlloc(arena, self.max_stdio_size);
            stdout_null = false;
        }
    } else if (child.stderr) |stderr| {
        stderr_bytes = try stderr.reader().readAllAlloc(arena, self.max_stdio_size);
        stderr_null = false;
    }

    if (!stderr_null and stderr_bytes.len > 0) {
        // Treat stderr as an error message.
        const stderr_is_diagnostic = self.captured_stderr == null and switch (self.stdio) {
            .check => |checks| !checksContainStderr(checks.items),
            else => true,
        };
        if (stderr_is_diagnostic) {
            try self.step.result_error_msgs.append(arena, stderr_bytes);
        }
    }

    return .{
        .stdout = stdout_bytes,
        .stderr = stderr_bytes,
        .stdout_null = stdout_null,
        .stderr_null = stderr_null,
        .test_results = .{},
        .test_metadata = null,
    };
}

fn addPathForDynLibs(self: *Run, artifact: *Step.Compile) void {
    const b = self.step.owner;
    for (artifact.link_objects.items) |link_object| {
        switch (link_object) {
            .other_step => |other| {
                if (other.target.isWindows() and other.isDynamicLibrary()) {
                    addPathDir(self, fs.path.dirname(other.getOutputSource().getPath(b)).?);
                    addPathForDynLibs(self, other);
                }
            },
            else => {},
        }
    }
}

fn failForeign(
    self: *Run,
    suggested_flag: []const u8,
    argv0: []const u8,
    exe: *Step.Compile,
) error{ MakeFailed, MakeSkipped, OutOfMemory } {
    switch (self.stdio) {
        .check, .zig_test => {
            if (self.skip_foreign_checks)
                return error.MakeSkipped;

            const b = self.step.owner;
            const host_name = try b.host.target.zigTriple(b.allocator);
            const foreign_name = try exe.target.zigTriple(b.allocator);

            return self.step.fail(
                \\unable to spawn foreign binary '{s}' ({s}) on host system ({s})
                \\  consider using {s} or enabling skip_foreign_checks in the Run step
            , .{ argv0, foreign_name, host_name, suggested_flag });
        },
        else => {
            return self.step.fail("unable to spawn foreign binary '{s}'", .{argv0});
        },
    }
}

fn hashStdIo(hh: *std.Build.Cache.HashHelper, stdio: StdIo) void {
    switch (stdio) {
        .infer_from_args, .inherit, .zig_test => {},
        .check => |checks| for (checks.items) |check| {
            hh.add(@as(std.meta.Tag(StdIo.Check), check));
            switch (check) {
                .expect_stderr_exact,
                .expect_stderr_match,
                .expect_stdout_exact,
                .expect_stdout_match,
                => |s| hh.addBytes(s),

                .expect_term => |term| {
                    hh.add(@as(std.meta.Tag(std.process.Child.Term), term));
                    switch (term) {
                        .Exited => |x| hh.add(x),
                        .Signal, .Stopped, .Unknown => |x| hh.add(x),
                    }
                },
            }
        },
    }
}