pub const Message = struct {
    pub const Header = extern struct {
        tag: Tag,
        /// Size of the body only; does not include this Header.
        bytes_len: u32,
    };

    pub const Tag = enum(u32) {
        /// Body is a UTF-8 string.
        zig_version,
        /// Body is an ErrorBundle.
        error_bundle,
        /// Body is a EmitDigest.
        emit_digest,
        /// Body is a TestMetadata
        test_metadata,
        /// Body is a TestResults
        test_results,
        /// Body is a series of strings, delimited by null bytes.
        /// Each string is a prefixed file path.
        /// The first byte indicates the file prefix path (see prefixes fields
        /// of Cache). This byte is sent over the wire incremented so that null
        /// bytes are not confused with string terminators.
        /// The remaining bytes is the file path relative to that prefix.
        /// The prefixes are hard-coded in Compilation.create (cwd, zig lib dir, local cache dir)
        file_system_inputs,
        /// Body is a u64le that indicates the file path within the cache used
        /// to store coverage information. The integer is a hash of the PCs
        /// stored within that file.
        coverage_id,
        /// Body is a u64le that indicates the function pointer virtual memory
        /// address of the fuzz unit test. This is used to provide a starting
        /// point to view coverage.
        fuzz_start_addr,

        _,
    };

    pub const PathPrefix = enum(u8) {
        cwd,
        zig_lib,
        local_cache,
        global_cache,
    };

    /// Trailing:
    /// * extra: [extra_len]u32,
    /// * string_bytes: [string_bytes_len]u8,
    /// See `std.zig.ErrorBundle`.
    pub const ErrorBundle = extern struct {
        extra_len: u32,
        string_bytes_len: u32,
    };

    /// Trailing:
    /// * name: [tests_len]u32
    ///   - null-terminated string_bytes index
    /// * expected_panic_msg: [tests_len]u32,
    ///   - null-terminated string_bytes index
    ///   - 0 means does not expect panic
    /// * string_bytes: [string_bytes_len]u8,
    pub const TestMetadata = extern struct {
        string_bytes_len: u32,
        tests_len: u32,
    };

    pub const TestResults = extern struct {
        index: u32,
        flags: Flags,

        pub const Flags = packed struct(u32) {
            fail: bool,
            skip: bool,
            leak: bool,
            fuzz: bool,
            log_err_count: u28 = 0,
        };
    };

    /// Trailing:
    /// * the hex digest of the cache directory within the /o/ subdirectory.
    pub const EmitDigest = extern struct {
        flags: Flags,

        pub const Flags = packed struct(u8) {
            cache_hit: bool,
            reserved: u7 = 0,
        };
    };
}