Fetch.zig

//! Represents one independent job whose responsibility is to:
//!
//! 1. Check the global zig package cache to see if the hash already exists.
//!    If so, load, parse, and validate the build.zig.zon file therein, and
//!    goto step 8. Likewise if the location is a relative path, treat this
//!    the same as a cache hit. Otherwise, proceed.
//! 2. Fetch and unpack a URL into a temporary directory.
//! 3. Load, parse, and validate the build.zig.zon file therein. It is allowed
//!    for the file to be missing, in which case this fetched package is considered
//!    to be a "naked" package.
//! 4. Apply inclusion rules of the build.zig.zon to the temporary directory by
//!    deleting excluded files. If any files had errors for files that were
//!    ultimately excluded, those errors should be ignored, such as failure to
//!    create symlinks that weren't supposed to be included anyway.
//! 5. Compute the package hash based on the remaining files in the temporary
//!    directory.
//! 6. Rename the temporary directory into the global zig package cache
//!    directory. If the hash already exists, delete the temporary directory and
//!    leave the zig package cache directory untouched as it may be in use by the
//!    system. This is done even if the hash is invalid, in case the package with
//!    the different hash is used in the future.
//! 7. Validate the computed hash against the expected hash. If invalid,
//!    this job is done.
//! 8. Spawn a new fetch job for each dependency in the manifest file. Use
//!    a mutex and a hash map so that redundant jobs do not get queued up.
//!
//! All of this must be done with only referring to the state inside this struct
//! because this work will be done in a dedicated thread.

arena: std.heap.ArenaAllocator,
location: Location,
location_tok: std.zig.Ast.TokenIndex,
hash_tok: std.zig.Ast.OptionalTokenIndex,
name_tok: std.zig.Ast.TokenIndex,
lazy_status: LazyStatus,
parent_package_root: Cache.Path,
parent_manifest_ast: ?*const std.zig.Ast,
prog_node: std.Progress.Node,
job_queue: *JobQueue,
/// If true, don't add an error for a missing hash. This flag is not passed
/// down to recursive dependencies. It's intended to be used only be the CLI.
omit_missing_hash_error: bool,
/// If true, don't fail when a manifest file is missing the `paths` field,
/// which specifies inclusion rules. This is intended to be true for the first
/// fetch task and false for the recursive dependencies.
allow_missing_paths_field: bool,
allow_missing_fingerprint: bool,
allow_name_string: bool,
/// If true and URL points to a Git repository, will use the latest commit.
use_latest_commit: bool,

// Above this are fields provided as inputs to `run`.
// Below this are fields populated by `run`.

/// This will either be relative to `global_cache`, or to the build root of
/// the root package.
package_root: Cache.Path,
error_bundle: ErrorBundle.Wip,
manifest: ?Manifest,
manifest_ast: std.zig.Ast,
computed_hash: ComputedHash,
/// Fetch logic notices whether a package has a build.zig file and sets this flag.
has_build_zig: bool,
/// Indicates whether the task aborted due to an out-of-memory condition.
oom_flag: bool,
/// If `use_latest_commit` was true, this will be set to the commit that was used.
/// If the resource pointed to by the location is not a Git-repository, this
/// will be left unchanged.
latest_commit: ?git.Oid,

// This field is used by the CLI only, untouched by this file.

/// The module for this `Fetch` tasks's package, which exposes `build.zig` as
/// the root source file.
module: ?*Package.Module,

pub const LazyStatus = enum {
    /// Not lazy.
    eager,
    /// Lazy, found.
    available,
    /// Lazy, not found.
    unavailable,
};

/// Contains shared state among all `Fetch` tasks.
pub const JobQueue = struct {
    mutex: std.Thread.Mutex = .{},
    /// It's an array hash map so that it can be sorted before rendering the
    /// dependencies.zig source file.
    /// Protected by `mutex`.
    table: Table = .{},
    /// `table` may be missing some tasks such as ones that failed, so this
    /// field contains references to all of them.
    /// Protected by `mutex`.
    all_fetches: std.ArrayListUnmanaged(*Fetch) = .empty,

    http_client: *std.http.Client,
    thread_pool: *ThreadPool,
    wait_group: WaitGroup = .{},
    global_cache: Cache.Directory,
    /// If true then, no fetching occurs, and:
    /// * The `global_cache` directory is assumed to be the direct parent
    ///   directory of on-disk packages rather than having the "p/" directory
    ///   prefix inside of it.
    /// * An error occurs if any non-lazy packages are not already present in
    ///   the package cache directory.
    /// * Missing hash field causes an error, and no fetching occurs so it does
    ///   not print the correct hash like usual.
    read_only: bool,
    recursive: bool,
    /// Dumps hash information to stdout which can be used to troubleshoot why
    /// two hashes of the same package do not match.
    /// If this is true, `recursive` must be false.
    debug_hash: bool,
    work_around_btrfs_bug: bool,
    mode: Mode,
    /// Set of hashes that will be additionally fetched even if they are marked
    /// as lazy.
    unlazy_set: UnlazySet = .{},

    pub const Mode = enum {
        /// Non-lazy dependencies are always fetched.
        /// Lazy dependencies are fetched only when needed.
        needed,
        /// Both non-lazy and lazy dependencies are always fetched.
        all,
    };
    pub const Table = std.AutoArrayHashMapUnmanaged(Package.Hash, *Fetch);
    pub const UnlazySet = std.AutoArrayHashMapUnmanaged(Package.Hash, void);

    pub fn deinit(jq: *JobQueue) void {
        if (jq.all_fetches.items.len == 0) return;
        const gpa = jq.all_fetches.items[0].arena.child_allocator;
        jq.table.deinit(gpa);
        // These must be deinitialized in reverse order because subsequent
        // `Fetch` instances are allocated in prior ones' arenas.
        // Sorry, I know it's a bit weird, but it slightly simplifies the
        // critical section.
        while (jq.all_fetches.pop()) |f| f.deinit();
        jq.all_fetches.deinit(gpa);
        jq.* = undefined;
    }

    /// Dumps all subsequent error bundles into the first one.
    pub fn consolidateErrors(jq: *JobQueue) !void {
        const root = &jq.all_fetches.items[0].error_bundle;
        const gpa = root.gpa;
        for (jq.all_fetches.items[1..]) |fetch| {
            if (fetch.error_bundle.root_list.items.len > 0) {
                var bundle = try fetch.error_bundle.toOwnedBundle("");
                defer bundle.deinit(gpa);
                try root.addBundleAsRoots(bundle);
            }
        }
    }

    /// Creates the dependencies.zig source code for the build runner to obtain
    /// via `@import("@dependencies")`.
    pub fn createDependenciesSource(jq: *JobQueue, buf: *std.ArrayList(u8)) Allocator.Error!void {
        const keys = jq.table.keys();

        assert(keys.len != 0); // caller should have added the first one
        if (keys.len == 1) {
            // This is the first one. It must have no dependencies.
            return createEmptyDependenciesSource(buf);
        }

        try buf.appendSlice("pub const packages = struct {\n");

        // Ensure the generated .zig file is deterministic.
        jq.table.sortUnstable(@as(struct {
            keys: []const Package.Hash,
            pub fn lessThan(ctx: @This(), a_index: usize, b_index: usize) bool {
                return std.mem.lessThan(u8, &ctx.keys[a_index].bytes, &ctx.keys[b_index].bytes);
            }
        }, .{ .keys = keys }));

        for (keys, jq.table.values()) |*hash, fetch| {
            if (fetch == jq.all_fetches.items[0]) {
                // The first one is a dummy package for the current project.
                continue;
            }

            const hash_slice = hash.toSlice();

            try buf.writer().print(
                \\    pub const {} = struct {{
                \\
            , .{std.zig.fmtId(hash_slice)});

            lazy: {
                switch (fetch.lazy_status) {
                    .eager => break :lazy,
                    .available => {
                        try buf.appendSlice(
                            \\        pub const available = true;
                            \\
                        );
                        break :lazy;
                    },
                    .unavailable => {
                        try buf.appendSlice(
                            \\        pub const available = false;
                            \\    };
                            \\
                        );
                        continue;
                    },
                }
            }

            try buf.writer().print(
                \\        pub const build_root = "{q}";
                \\
            , .{fetch.package_root});

            if (fetch.has_build_zig) {
                try buf.writer().print(
                    \\        pub const build_zig = @import("{}");
                    \\
                , .{std.zig.fmtEscapes(hash_slice)});
            }

            if (fetch.manifest) |*manifest| {
                try buf.appendSlice(
                    \\        pub const deps: []const struct { []const u8, []const u8 } = &.{
                    \\
                );
                for (manifest.dependencies.keys(), manifest.dependencies.values()) |name, dep| {
                    const h = depDigest(fetch.package_root, jq.global_cache, dep) orelse continue;
                    try buf.writer().print(
                        "            .{{ \"{}\", \"{}\" }},\n",
                        .{ std.zig.fmtEscapes(name), std.zig.fmtEscapes(h.toSlice()) },
                    );
                }

                try buf.appendSlice(
                    \\        };
                    \\    };
                    \\
                );
            } else {
                try buf.appendSlice(
                    \\        pub const deps: []const struct { []const u8, []const u8 } = &.{};
                    \\    };
                    \\
                );
            }
        }

        try buf.appendSlice(
            \\};
            \\
            \\pub const root_deps: []const struct { []const u8, []const u8 } = &.{
            \\
        );

        const root_fetch = jq.all_fetches.items[0];
        const root_manifest = &root_fetch.manifest.?;

        for (root_manifest.dependencies.keys(), root_manifest.dependencies.values()) |name, dep| {
            const h = depDigest(root_fetch.package_root, jq.global_cache, dep) orelse continue;
            try buf.writer().print(
                "    .{{ \"{}\", \"{}\" }},\n",
                .{ std.zig.fmtEscapes(name), std.zig.fmtEscapes(h.toSlice()) },
            );
        }
        try buf.appendSlice("};\n");
    }

    pub fn createEmptyDependenciesSource(buf: *std.ArrayList(u8)) Allocator.Error!void {
        try buf.appendSlice(
            \\pub const packages = struct {};
            \\pub const root_deps: []const struct { []const u8, []const u8 } = &.{};
            \\
        );
    }
};

pub const Location = union(enum) {
    remote: Remote,
    /// A directory found inside the parent package.
    relative_path: Cache.Path,
    /// Recursive Fetch tasks will never use this Location, but it may be
    /// passed in by the CLI. Indicates the file contents here should be copied
    /// into the global package cache. It may be a file relative to the cwd or
    /// absolute, in which case it should be treated exactly like a `file://`
    /// URL, or a directory, in which case it should be treated as an
    /// already-unpacked directory (but still needs to be copied into the
    /// global package cache and have inclusion rules applied).
    path_or_url: []const u8,

    pub const Remote = struct {
        url: []const u8,
        /// If this is null it means the user omitted the hash field from a dependency.
        /// It will be an error but the logic should still fetch and print the discovered hash.
        hash: ?Package.Hash,
    };
};

pub const RunError = error{
    OutOfMemory,
    /// This error code is intended to be handled by inspecting the
    /// `error_bundle` field.
    FetchFailed,
};

pub fn run(f: *Fetch) RunError!void {
    const eb = &f.error_bundle;
    const arena = f.arena.allocator();
    const gpa = f.arena.child_allocator;
    const cache_root = f.job_queue.global_cache;

    try eb.init(gpa);

    // Check the global zig package cache to see if the hash already exists. If
    // so, load, parse, and validate the build.zig.zon file therein, and skip
    // ahead to queuing up jobs for dependencies. Likewise if the location is a
    // relative path, treat this the same as a cache hit. Otherwise, proceed.

    const remote = switch (f.location) {
        .relative_path => |pkg_root| {
            if (fs.path.isAbsolute(pkg_root.sub_path)) return f.fail(
                f.location_tok,
                try eb.addString("expected path relative to build root; found absolute path"),
            );
            if (f.hash_tok.unwrap()) |hash_tok| return f.fail(
                hash_tok,
                try eb.addString("path-based dependencies are not hashed"),
            );
            // Packages fetched by URL may not use relative paths to escape outside the
            // fetched package directory from within the package cache.
            if (pkg_root.root_dir.eql(cache_root)) {
                // `parent_package_root.sub_path` contains a path like this:
                // "p/$hash", or
                // "p/$hash/foo", with possibly more directories after "foo".
                // We want to fail unless the resolved relative path has a
                // prefix of "p/$hash/".
                const prefix_len: usize = if (f.job_queue.read_only) 0 else "p/".len;
                const parent_sub_path = f.parent_package_root.sub_path;
                const end = find_end: {
                    if (parent_sub_path.len > prefix_len) {
                        // Use `isSep` instead of `indexOfScalarPos` to account for
                        // Windows accepting both `\` and `/` as path separators.
                        for (parent_sub_path[prefix_len..], prefix_len..) |c, i| {
                            if (std.fs.path.isSep(c)) break :find_end i;
                        }
                    }
                    break :find_end parent_sub_path.len;
                };
                const expected_prefix = parent_sub_path[0..end];
                if (!std.mem.startsWith(u8, pkg_root.sub_path, expected_prefix)) {
                    return f.fail(
                        f.location_tok,
                        try eb.printString("dependency path outside project: '{}'", .{pkg_root}),
                    );
                }
            }
            f.package_root = pkg_root;
            try loadManifest(f, pkg_root);
            if (!f.has_build_zig) try checkBuildFileExistence(f);
            if (!f.job_queue.recursive) return;
            return queueJobsForDeps(f);
        },
        .remote => |remote| remote,
        .path_or_url => |path_or_url| {
            if (fs.cwd().openDir(path_or_url, .{ .iterate = true })) |dir| {
                var resource: Resource = .{ .dir = dir };
                return f.runResource(path_or_url, &resource, null);
            } else |dir_err| {
                const file_err = if (dir_err == error.NotDir) e: {
                    if (fs.cwd().openFile(path_or_url, .{})) |file| {
                        var resource: Resource = .{ .file = file };
                        return f.runResource(path_or_url, &resource, null);
                    } else |err| break :e err;
                } else dir_err;

                const uri = std.Uri.parse(path_or_url) catch |uri_err| {
                    return f.fail(0, try eb.printString(
                        "'{s}' could not be recognized as a file path ({s}) or an URL ({s})",
                        .{ path_or_url, @errorName(file_err), @errorName(uri_err) },
                    ));
                };
                var server_header_buffer: [header_buffer_size]u8 = undefined;
                var resource = try f.initResource(uri, &server_header_buffer);
                return f.runResource(try uri.path.toRawMaybeAlloc(arena), &resource, null);
            }
        },
    };

    if (remote.hash) |expected_hash| {
        var prefixed_pkg_sub_path_buffer: [Package.Hash.max_len + 2]u8 = undefined;
        prefixed_pkg_sub_path_buffer[0] = 'p';
        prefixed_pkg_sub_path_buffer[1] = fs.path.sep;
        const hash_slice = expected_hash.toSlice();
        @memcpy(prefixed_pkg_sub_path_buffer[2..][0..hash_slice.len], hash_slice);
        const prefixed_pkg_sub_path = prefixed_pkg_sub_path_buffer[0 .. 2 + hash_slice.len];
        const prefix_len: usize = if (f.job_queue.read_only) "p/".len else 0;
        const pkg_sub_path = prefixed_pkg_sub_path[prefix_len..];
        if (cache_root.handle.access(pkg_sub_path, .{})) |_| {
            assert(f.lazy_status != .unavailable);
            f.package_root = .{
                .root_dir = cache_root,
                .sub_path = try arena.dupe(u8, pkg_sub_path),
            };
            try loadManifest(f, f.package_root);
            try checkBuildFileExistence(f);
            if (!f.job_queue.recursive) return;
            return queueJobsForDeps(f);
        } else |err| switch (err) {
            error.FileNotFound => {
                switch (f.lazy_status) {
                    .eager => {},
                    .available => if (!f.job_queue.unlazy_set.contains(expected_hash)) {
                        f.lazy_status = .unavailable;
                        return;
                    },
                    .unavailable => unreachable,
                }
                if (f.job_queue.read_only) return f.fail(
                    f.name_tok,
                    try eb.printString("package not found at '{}{s}'", .{
                        cache_root, pkg_sub_path,
                    }),
                );
            },
            else => |e| {
                try eb.addRootErrorMessage(.{
                    .msg = try eb.printString("unable to open global package cache directory '{}{s}': {s}", .{
                        cache_root, pkg_sub_path, @errorName(e),
                    }),
                });
                return error.FetchFailed;
            },
        }
    } else if (f.job_queue.read_only) {
        try eb.addRootErrorMessage(.{
            .msg = try eb.addString("dependency is missing hash field"),
            .src_loc = try f.srcLoc(f.location_tok),
        });
        return error.FetchFailed;
    }

    // Fetch and unpack the remote into a temporary directory.

    const uri = std.Uri.parse(remote.url) catch |err| return f.fail(
        f.location_tok,
        try eb.printString("invalid URI: {s}", .{@errorName(err)}),
    );
    var server_header_buffer: [header_buffer_size]u8 = undefined;
    var resource = try f.initResource(uri, &server_header_buffer);
    return f.runResource(try uri.path.toRawMaybeAlloc(arena), &resource, remote.hash);
}

pub fn deinit(f: *Fetch) void {
    f.error_bundle.deinit();
    f.arena.deinit();
}

/// Consumes `resource`, even if an error is returned.
fn runResource(
    f: *Fetch,
    uri_path: []const u8,
    resource: *Resource,
    remote_hash: ?Package.Hash,
) RunError!void {
    defer resource.deinit();
    const arena = f.arena.allocator();
    const eb = &f.error_bundle;
    const s = fs.path.sep_str;
    const cache_root = f.job_queue.global_cache;
    const rand_int = std.crypto.random.int(u64);
    const tmp_dir_sub_path = "tmp" ++ s ++ std.fmt.hex(rand_int);

    const package_sub_path = blk: {
        const tmp_directory_path = try cache_root.join(arena, &.{tmp_dir_sub_path});
        var tmp_directory: Cache.Directory = .{
            .path = tmp_directory_path,
            .handle = handle: {
                const dir = cache_root.handle.makeOpenPath(tmp_dir_sub_path, .{
                    .iterate = true,
                }) catch |err| {
                    try eb.addRootErrorMessage(.{
                        .msg = try eb.printString("unable to create temporary directory '{s}': {s}", .{
                            tmp_directory_path, @errorName(err),
                        }),
                    });
                    return error.FetchFailed;
                };
                break :handle dir;
            },
        };
        defer tmp_directory.handle.close();

        // Fetch and unpack a resource into a temporary directory.
        var unpack_result = try unpackResource(f, resource, uri_path, tmp_directory);

        var pkg_path: Cache.Path = .{ .root_dir = tmp_directory, .sub_path = unpack_result.root_dir };

        // Apply btrfs workaround if needed. Reopen tmp_directory.
        if (native_os == .linux and f.job_queue.work_around_btrfs_bug) {
            // https://github.com/ziglang/zig/issues/17095
            pkg_path.root_dir.handle.close();
            pkg_path.root_dir.handle = cache_root.handle.makeOpenPath(tmp_dir_sub_path, .{
                .iterate = true,
            }) catch @panic("btrfs workaround failed");
        }

        // Load, parse, and validate the unpacked build.zig.zon file. It is allowed
        // for the file to be missing, in which case this fetched package is
        // considered to be a "naked" package.
        try loadManifest(f, pkg_path);

        const filter: Filter = .{
            .include_paths = if (f.manifest) |m| m.paths else .{},
        };

        // Ignore errors that were excluded by manifest, such as failure to
        // create symlinks that weren't supposed to be included anyway.
        try unpack_result.validate(f, filter);

        // Apply the manifest's inclusion rules to the temporary directory by
        // deleting excluded files.
        // Empty directories have already been omitted by `unpackResource`.
        // Compute the package hash based on the remaining files in the temporary
        // directory.
        f.computed_hash = try computeHash(f, pkg_path, filter);

        break :blk if (unpack_result.root_dir.len > 0)
            try fs.path.join(arena, &.{ tmp_dir_sub_path, unpack_result.root_dir })
        else
            tmp_dir_sub_path;
    };

    const computed_package_hash = computedPackageHash(f);

    // Rename the temporary directory into the global zig package cache
    // directory. If the hash already exists, delete the temporary directory
    // and leave the zig package cache directory untouched as it may be in use
    // by the system. This is done even if the hash is invalid, in case the
    // package with the different hash is used in the future.

    f.package_root = .{
        .root_dir = cache_root,
        .sub_path = try std.fmt.allocPrint(arena, "p" ++ s ++ "{s}", .{computed_package_hash.toSlice()}),
    };
    renameTmpIntoCache(cache_root.handle, package_sub_path, f.package_root.sub_path) catch |err| {
        const src = try cache_root.join(arena, &.{tmp_dir_sub_path});
        const dest = try cache_root.join(arena, &.{f.package_root.sub_path});
        try eb.addRootErrorMessage(.{ .msg = try eb.printString(
            "unable to rename temporary directory '{s}' into package cache directory '{s}': {s}",
            .{ src, dest, @errorName(err) },
        ) });
        return error.FetchFailed;
    };
    // Remove temporary directory root if not already renamed to global cache.
    if (!std.mem.eql(u8, package_sub_path, tmp_dir_sub_path)) {
        cache_root.handle.deleteDir(tmp_dir_sub_path) catch {};
    }

    // Validate the computed hash against the expected hash. If invalid, this
    // job is done.

    if (remote_hash) |declared_hash| {
        const hash_tok = f.hash_tok.unwrap().?;
        if (declared_hash.isOld()) {
            const actual_hex = Package.multiHashHexDigest(f.computed_hash.digest);
            if (!std.mem.eql(u8, declared_hash.toSlice(), &actual_hex)) {
                return f.fail(hash_tok, try eb.printString(
                    "hash mismatch: manifest declares {s} but the fetched package has {s}",
                    .{ declared_hash.toSlice(), actual_hex },
                ));
            }
        } else {
            if (!computed_package_hash.eql(&declared_hash)) {
                return f.fail(hash_tok, try eb.printString(
                    "hash mismatch: manifest declares {s} but the fetched package has {s}",
                    .{ declared_hash.toSlice(), computed_package_hash.toSlice() },
                ));
            }
        }
    } else if (!f.omit_missing_hash_error) {
        const notes_len = 1;
        try eb.addRootErrorMessage(.{
            .msg = try eb.addString("dependency is missing hash field"),
            .src_loc = try f.srcLoc(f.location_tok),
            .notes_len = notes_len,
        });
        const notes_start = try eb.reserveNotes(notes_len);
        eb.extra.items[notes_start] = @intFromEnum(try eb.addErrorMessage(.{
            .msg = try eb.printString("expected .hash = \"{s}\",", .{computed_package_hash.toSlice()}),
        }));
        return error.FetchFailed;
    }

    // Spawn a new fetch job for each dependency in the manifest file. Use
    // a mutex and a hash map so that redundant jobs do not get queued up.
    if (!f.job_queue.recursive) return;
    return queueJobsForDeps(f);
}

pub fn computedPackageHash(f: *const Fetch) Package.Hash {
    const saturated_size = std.math.cast(u32, f.computed_hash.total_size) orelse std.math.maxInt(u32);
    if (f.manifest) |man| {
        var version_buffer: [32]u8 = undefined;
        const version: []const u8 = std.fmt.bufPrint(&version_buffer, "{}", .{man.version}) catch &version_buffer;
        return .init(f.computed_hash.digest, man.name, version, man.id, saturated_size);
    }
    // In the future build.zig.zon fields will be added to allow overriding these values
    // for naked tarballs.
    return .init(f.computed_hash.digest, "N", "V", 0xffff, saturated_size);
}

/// `computeHash` gets a free check for the existence of `build.zig`, but when
/// not computing a hash, we need to do a syscall to check for it.
fn checkBuildFileExistence(f: *Fetch) RunError!void {
    const eb = &f.error_bundle;
    if (f.package_root.access(Package.build_zig_basename, .{})) |_| {
        f.has_build_zig = true;
    } else |err| switch (err) {
        error.FileNotFound => {},
        else => |e| {
            try eb.addRootErrorMessage(.{
                .msg = try eb.printString("unable to access '{}{s}': {s}", .{
                    f.package_root, Package.build_zig_basename, @errorName(e),
                }),
            });
            return error.FetchFailed;
        },
    }
}

/// This function populates `f.manifest` or leaves it `null`.
fn loadManifest(f: *Fetch, pkg_root: Cache.Path) RunError!void {
    const eb = &f.error_bundle;
    const arena = f.arena.allocator();
    const manifest_bytes = pkg_root.root_dir.handle.readFileAllocOptions(
        arena,
        try fs.path.join(arena, &.{ pkg_root.sub_path, Manifest.basename }),
        Manifest.max_bytes,
        null,
        1,
        0,
    ) catch |err| switch (err) {
        error.FileNotFound => return,
        else => |e| {
            const file_path = try pkg_root.join(arena, Manifest.basename);
            try eb.addRootErrorMessage(.{
                .msg = try eb.printString("unable to load package manifest '{}': {s}", .{
                    file_path, @errorName(e),
                }),
            });
            return error.FetchFailed;
        },
    };

    const ast = &f.manifest_ast;
    ast.* = try std.zig.Ast.parse(arena, manifest_bytes, .zon);

    if (ast.errors.len > 0) {
        const file_path = try std.fmt.allocPrint(arena, "{}" ++ fs.path.sep_str ++ Manifest.basename, .{pkg_root});
        try std.zig.putAstErrorsIntoBundle(arena, ast.*, file_path, eb);
        return error.FetchFailed;
    }

    f.manifest = try Manifest.parse(arena, ast.*, .{
        .allow_missing_paths_field = f.allow_missing_paths_field,
        .allow_missing_fingerprint = f.allow_missing_fingerprint,
        .allow_name_string = f.allow_name_string,
    });
    const manifest = &f.manifest.?;

    if (manifest.errors.len > 0) {
        const src_path = try eb.printString("{}" ++ fs.path.sep_str ++ "{s}", .{ pkg_root, Manifest.basename });
        try manifest.copyErrorsIntoBundle(ast.*, src_path, eb);
        return error.FetchFailed;
    }
}

fn queueJobsForDeps(f: *Fetch) RunError!void {
    assert(f.job_queue.recursive);

    // If the package does not have a build.zig.zon file then there are no dependencies.
    const manifest = f.manifest orelse return;

    const new_fetches, const prog_names = nf: {
        const parent_arena = f.arena.allocator();
        const gpa = f.arena.child_allocator;
        const cache_root = f.job_queue.global_cache;
        const dep_names = manifest.dependencies.keys();
        const deps = manifest.dependencies.values();
        // Grab the new tasks into a temporary buffer so we can unlock that mutex
        // as fast as possible.
        // This overallocates any fetches that get skipped by the `continue` in the
        // loop below.
        const new_fetches = try parent_arena.alloc(Fetch, deps.len);
        const prog_names = try parent_arena.alloc([]const u8, deps.len);
        var new_fetch_index: usize = 0;

        f.job_queue.mutex.lock();
        defer f.job_queue.mutex.unlock();

        try f.job_queue.all_fetches.ensureUnusedCapacity(gpa, new_fetches.len);
        try f.job_queue.table.ensureUnusedCapacity(gpa, @intCast(new_fetches.len));

        // There are four cases here:
        // * Correct hash is provided by manifest.
        //   - Hash map already has the entry, no need to add it again.
        // * Incorrect hash is provided by manifest.
        //   - Hash mismatch error emitted; `queueJobsForDeps` is not called.
        // * Hash is not provided by manifest.
        //   - Hash missing error emitted; `queueJobsForDeps` is not called.
        // * path-based location is used without a hash.
        //   - Hash is added to the table based on the path alone before
        //     calling run(); no need to add it again.
        //
        // If we add a dep as lazy and then later try to add the same dep as eager,
        // eagerness takes precedence and the existing entry is updated.

        for (dep_names, deps) |dep_name, dep| {
            const new_fetch = &new_fetches[new_fetch_index];
            const location: Location = switch (dep.location) {
                .url => |url| .{ .remote = .{
                    .url = url,
                    .hash = h: {
                        const h = dep.hash orelse break :h null;
                        const pkg_hash: Package.Hash = .fromSlice(h);
                        const gop = f.job_queue.table.getOrPutAssumeCapacity(pkg_hash);
                        if (gop.found_existing) {
                            if (!dep.lazy) {
                                gop.value_ptr.*.lazy_status = .eager;
                            }
                            continue;
                        }
                        gop.value_ptr.* = new_fetch;
                        break :h pkg_hash;
                    },
                } },
                .path => |rel_path| l: {
                    // This might produce an invalid path, which is checked for
                    // at the beginning of run().
                    const new_root = try f.package_root.resolvePosix(parent_arena, rel_path);
                    const pkg_hash = relativePathDigest(new_root, cache_root);
                    const gop = f.job_queue.table.getOrPutAssumeCapacity(pkg_hash);
                    if (gop.found_existing) {
                        if (!dep.lazy) {
                            gop.value_ptr.*.lazy_status = .eager;
                        }
                        continue;
                    }
                    gop.value_ptr.* = new_fetch;
                    break :l .{ .relative_path = new_root };
                },
            };
            prog_names[new_fetch_index] = dep_name;
            new_fetch_index += 1;
            f.job_queue.all_fetches.appendAssumeCapacity(new_fetch);
            new_fetch.* = .{
                .arena = std.heap.ArenaAllocator.init(gpa),
                .location = location,
                .location_tok = dep.location_tok,
                .hash_tok = dep.hash_tok,
                .name_tok = dep.name_tok,
                .lazy_status = switch (f.job_queue.mode) {
                    .needed => if (dep.lazy) .available else .eager,
                    .all => .eager,
                },
                .parent_package_root = f.package_root,
                .parent_manifest_ast = &f.manifest_ast,
                .prog_node = f.prog_node,
                .job_queue = f.job_queue,
                .omit_missing_hash_error = false,
                .allow_missing_paths_field = true,
                .allow_missing_fingerprint = true,
                .allow_name_string = true,
                .use_latest_commit = false,

                .package_root = undefined,
                .error_bundle = undefined,
                .manifest = null,
                .manifest_ast = undefined,
                .computed_hash = undefined,
                .has_build_zig = false,
                .oom_flag = false,
                .latest_commit = null,

                .module = null,
            };
        }

        f.prog_node.increaseEstimatedTotalItems(new_fetch_index);

        break :nf .{ new_fetches[0..new_fetch_index], prog_names[0..new_fetch_index] };
    };

    // Now it's time to give tasks to the thread pool.
    const thread_pool = f.job_queue.thread_pool;

    for (new_fetches, prog_names) |*new_fetch, prog_name| {
        thread_pool.spawnWg(&f.job_queue.wait_group, workerRun, .{ new_fetch, prog_name });
    }
}

pub fn relativePathDigest(pkg_root: Cache.Path, cache_root: Cache.Directory) Package.Hash {
    return .initPath(pkg_root.sub_path, pkg_root.root_dir.eql(cache_root));
}

pub fn workerRun(f: *Fetch, prog_name: []const u8) void {
    const prog_node = f.prog_node.start(prog_name, 0);
    defer prog_node.end();

    run(f) catch |err| switch (err) {
        error.OutOfMemory => f.oom_flag = true,
        error.FetchFailed => {
            // Nothing to do because the errors are already reported in `error_bundle`,
            // and a reference is kept to the `Fetch` task inside `all_fetches`.
        },
    };
}

fn srcLoc(
    f: *Fetch,
    tok: std.zig.Ast.TokenIndex,
) Allocator.Error!ErrorBundle.SourceLocationIndex {
    const ast = f.parent_manifest_ast orelse return .none;
    const eb = &f.error_bundle;
    const start_loc = ast.tokenLocation(0, tok);
    const src_path = try eb.printString("{}" ++ fs.path.sep_str ++ Manifest.basename, .{f.parent_package_root});
    const msg_off = 0;
    return eb.addSourceLocation(.{
        .src_path = src_path,
        .span_start = ast.tokenStart(tok),
        .span_end = @intCast(ast.tokenStart(tok) + ast.tokenSlice(tok).len),
        .span_main = ast.tokenStart(tok) + msg_off,
        .line = @intCast(start_loc.line),
        .column = @intCast(start_loc.column),
        .source_line = try eb.addString(ast.source[start_loc.line_start..start_loc.line_end]),
    });
}

fn fail(f: *Fetch, msg_tok: std.zig.Ast.TokenIndex, msg_str: u32) RunError {
    const eb = &f.error_bundle;
    try eb.addRootErrorMessage(.{
        .msg = msg_str,
        .src_loc = try f.srcLoc(msg_tok),
    });
    return error.FetchFailed;
}

const Resource = union(enum) {
    file: fs.File,
    http_request: std.http.Client.Request,
    git: Git,
    dir: fs.Dir,

    const Git = struct {
        session: git.Session,
        fetch_stream: git.Session.FetchStream,
        want_oid: git.Oid,
    };

    fn deinit(resource: *Resource) void {
        switch (resource.*) {
            .file => |*file| file.close(),
            .http_request => |*req| req.deinit(),
            .git => |*git_resource| {
                git_resource.fetch_stream.deinit();
                git_resource.session.deinit();
            },
            .dir => |*dir| dir.close(),
        }
        resource.* = undefined;
    }

    fn reader(resource: *Resource) std.io.AnyReader {
        return .{
            .context = resource,
            .readFn = read,
        };
    }

    fn read(context: *const anyopaque, buffer: []u8) anyerror!usize {
        const resource: *Resource = @constCast(@ptrCast(@alignCast(context)));
        switch (resource.*) {
            .file => |*f| return f.read(buffer),
            .http_request => |*r| return r.read(buffer),
            .git => |*g| return g.fetch_stream.read(buffer),
            .dir => unreachable,
        }
    }
};

const FileType = enum {
    tar,
    @"tar.gz",
    @"tar.xz",
    @"tar.zst",
    git_pack,
    zip,

    fn fromPath(file_path: []const u8) ?FileType {
        if (ascii.endsWithIgnoreCase(file_path, ".tar")) return .tar;
        if (ascii.endsWithIgnoreCase(file_path, ".tgz")) return .@"tar.gz";
        if (ascii.endsWithIgnoreCase(file_path, ".tar.gz")) return .@"tar.gz";
        if (ascii.endsWithIgnoreCase(file_path, ".txz")) return .@"tar.xz";
        if (ascii.endsWithIgnoreCase(file_path, ".tar.xz")) return .@"tar.xz";
        if (ascii.endsWithIgnoreCase(file_path, ".tzst")) return .@"tar.zst";
        if (ascii.endsWithIgnoreCase(file_path, ".tar.zst")) return .@"tar.zst";
        if (ascii.endsWithIgnoreCase(file_path, ".zip")) return .zip;
        return null;
    }

    /// Parameter is a content-disposition header value.
    fn fromContentDisposition(cd_header: []const u8) ?FileType {
        const attach_end = ascii.indexOfIgnoreCase(cd_header, "attachment;") orelse
            return null;

        var value_start = ascii.indexOfIgnoreCasePos(cd_header, attach_end + 1, "filename") orelse
            return null;
        value_start += "filename".len;
        if (cd_header[value_start] == '*') {
            value_start += 1;
        }
        if (cd_header[value_start] != '=') return null;
        value_start += 1;

        var value_end = std.mem.indexOfPos(u8, cd_header, value_start, ";") orelse cd_header.len;
        if (cd_header[value_end - 1] == '\"') {
            value_end -= 1;
        }
        return fromPath(cd_header[value_start..value_end]);
    }

    test fromContentDisposition {
        try std.testing.expectEqual(@as(?FileType, .@"tar.gz"), fromContentDisposition("attaChment; FILENAME=\"stuff.tar.gz\"; size=42"));
        try std.testing.expectEqual(@as(?FileType, .@"tar.gz"), fromContentDisposition("attachment; filename*=\"stuff.tar.gz\""));
        try std.testing.expectEqual(@as(?FileType, .@"tar.xz"), fromContentDisposition("ATTACHMENT; filename=\"stuff.tar.xz\""));
        try std.testing.expectEqual(@as(?FileType, .@"tar.xz"), fromContentDisposition("attachment; FileName=\"stuff.tar.xz\""));
        try std.testing.expectEqual(@as(?FileType, .@"tar.gz"), fromContentDisposition("attachment; FileName*=UTF-8\'\'xyz%2Fstuff.tar.gz"));
        try std.testing.expectEqual(@as(?FileType, .tar), fromContentDisposition("attachment; FileName=\"stuff.tar\""));

        try std.testing.expect(fromContentDisposition("attachment FileName=\"stuff.tar.gz\"") == null);
        try std.testing.expect(fromContentDisposition("attachment; FileName\"stuff.gz\"") == null);
        try std.testing.expect(fromContentDisposition("attachment; size=42") == null);
        try std.testing.expect(fromContentDisposition("inline; size=42") == null);
        try std.testing.expect(fromContentDisposition("FileName=\"stuff.tar.gz\"; attachment;") == null);
        try std.testing.expect(fromContentDisposition("FileName=\"stuff.tar.gz\";") == null);
    }
};

const header_buffer_size = 16 * 1024;

fn initResource(f: *Fetch, uri: std.Uri, server_header_buffer: []u8) RunError!Resource {
    const gpa = f.arena.child_allocator;
    const arena = f.arena.allocator();
    const eb = &f.error_bundle;

    if (ascii.eqlIgnoreCase(uri.scheme, "file")) {
        const path = try uri.path.toRawMaybeAlloc(arena);
        return .{ .file = f.parent_package_root.openFile(path, .{}) catch |err| {
            return f.fail(f.location_tok, try eb.printString("unable to open '{}{s}': {s}", .{
                f.parent_package_root, path, @errorName(err),
            }));
        } };
    }

    const http_client = f.job_queue.http_client;

    if (ascii.eqlIgnoreCase(uri.scheme, "http") or
        ascii.eqlIgnoreCase(uri.scheme, "https"))
    {
        var req = http_client.open(.GET, uri, .{
            .server_header_buffer = server_header_buffer,
        }) catch |err| {
            return f.fail(f.location_tok, try eb.printString(
                "unable to connect to server: {s}",
                .{@errorName(err)},
            ));
        };
        errdefer req.deinit(); // releases more than memory

        req.send() catch |err| {
            return f.fail(f.location_tok, try eb.printString(
                "HTTP request failed: {s}",
                .{@errorName(err)},
            ));
        };
        req.wait() catch |err| {
            return f.fail(f.location_tok, try eb.printString(
                "invalid HTTP response: {s}",
                .{@errorName(err)},
            ));
        };

        if (req.response.status != .ok) {
            return f.fail(f.location_tok, try eb.printString(
                "bad HTTP response code: '{d} {s}'",
                .{ @intFromEnum(req.response.status), req.response.status.phrase() orelse "" },
            ));
        }

        return .{ .http_request = req };
    }

    if (ascii.eqlIgnoreCase(uri.scheme, "git+http") or
        ascii.eqlIgnoreCase(uri.scheme, "git+https"))
    {
        var transport_uri = uri;
        transport_uri.scheme = uri.scheme["git+".len..];
        var session = git.Session.init(gpa, http_client, transport_uri, server_header_buffer) catch |err| {
            return f.fail(f.location_tok, try eb.printString(
                "unable to discover remote git server capabilities: {s}",
                .{@errorName(err)},
            ));
        };
        errdefer session.deinit();

        const want_oid = want_oid: {
            const want_ref =
                if (uri.fragment) |fragment| try fragment.toRawMaybeAlloc(arena) else "HEAD";
            if (git.Oid.parseAny(want_ref)) |oid| break :want_oid oid else |_| {}

            const want_ref_head = try std.fmt.allocPrint(arena, "refs/heads/{s}", .{want_ref});
            const want_ref_tag = try std.fmt.allocPrint(arena, "refs/tags/{s}", .{want_ref});

            var ref_iterator = session.listRefs(.{
                .ref_prefixes = &.{ want_ref, want_ref_head, want_ref_tag },
                .include_peeled = true,
                .server_header_buffer = server_header_buffer,
            }) catch |err| {
                return f.fail(f.location_tok, try eb.printString(
                    "unable to list refs: {s}",
                    .{@errorName(err)},
                ));
            };
            defer ref_iterator.deinit();
            while (ref_iterator.next() catch |err| {
                return f.fail(f.location_tok, try eb.printString(
                    "unable to iterate refs: {s}",
                    .{@errorName(err)},
                ));
            }) |ref| {
                if (std.mem.eql(u8, ref.name, want_ref) or
                    std.mem.eql(u8, ref.name, want_ref_head) or
                    std.mem.eql(u8, ref.name, want_ref_tag))
                {
                    break :want_oid ref.peeled orelse ref.oid;
                }
            }
            return f.fail(f.location_tok, try eb.printString("ref not found: {s}", .{want_ref}));
        };
        if (f.use_latest_commit) {
            f.latest_commit = want_oid;
        } else if (uri.fragment == null) {
            const notes_len = 1;
            try eb.addRootErrorMessage(.{
                .msg = try eb.addString("url field is missing an explicit ref"),
                .src_loc = try f.srcLoc(f.location_tok),
                .notes_len = notes_len,
            });
            const notes_start = try eb.reserveNotes(notes_len);
            eb.extra.items[notes_start] = @intFromEnum(try eb.addErrorMessage(.{
                .msg = try eb.printString("try .url = \"{;+/}#{}\",", .{ uri, want_oid }),
            }));
            return error.FetchFailed;
        }

        var want_oid_buf: [git.Oid.max_formatted_length]u8 = undefined;
        _ = std.fmt.bufPrint(&want_oid_buf, "{}", .{want_oid}) catch unreachable;
        var fetch_stream = session.fetch(&.{&want_oid_buf}, server_header_buffer) catch |err| {
            return f.fail(f.location_tok, try eb.printString(
                "unable to create fetch stream: {s}",
                .{@errorName(err)},
            ));
        };
        errdefer fetch_stream.deinit();

        return .{ .git = .{
            .session = session,
            .fetch_stream = fetch_stream,
            .want_oid = want_oid,
        } };
    }

    return f.fail(f.location_tok, try eb.printString(
        "unsupported URL scheme: {s}",
        .{uri.scheme},
    ));
}

fn unpackResource(
    f: *Fetch,
    resource: *Resource,
    uri_path: []const u8,
    tmp_directory: Cache.Directory,
) RunError!UnpackResult {
    const eb = &f.error_bundle;
    const file_type = switch (resource.*) {
        .file => FileType.fromPath(uri_path) orelse
            return f.fail(f.location_tok, try eb.printString("unknown file type: '{s}'", .{uri_path})),

        .http_request => |req| ft: {
            // Content-Type takes first precedence.
            const content_type = req.response.content_type orelse
                return f.fail(f.location_tok, try eb.addString("missing 'Content-Type' header"));

            // Extract the MIME type, ignoring charset and boundary directives
            const mime_type_end = std.mem.indexOf(u8, content_type, ";") orelse content_type.len;
            const mime_type = content_type[0..mime_type_end];

            if (ascii.eqlIgnoreCase(mime_type, "application/x-tar"))
                break :ft .tar;

            if (ascii.eqlIgnoreCase(mime_type, "application/gzip") or
                ascii.eqlIgnoreCase(mime_type, "application/x-gzip") or
                ascii.eqlIgnoreCase(mime_type, "application/tar+gzip") or
                ascii.eqlIgnoreCase(mime_type, "application/x-tar-gz") or
                ascii.eqlIgnoreCase(mime_type, "application/x-gtar-compressed"))
            {
                break :ft .@"tar.gz";
            }

            if (ascii.eqlIgnoreCase(mime_type, "application/x-xz"))
                break :ft .@"tar.xz";

            if (ascii.eqlIgnoreCase(mime_type, "application/zstd"))
                break :ft .@"tar.zst";

            if (ascii.eqlIgnoreCase(mime_type, "application/zip"))
                break :ft .zip;

            if (!ascii.eqlIgnoreCase(mime_type, "application/octet-stream") and
                !ascii.eqlIgnoreCase(mime_type, "application/x-compressed"))
            {
                return f.fail(f.location_tok, try eb.printString(
                    "unrecognized 'Content-Type' header: '{s}'",
                    .{content_type},
                ));
            }

            // Next, the filename from 'content-disposition: attachment' takes precedence.
            if (req.response.content_disposition) |cd_header| {
                break :ft FileType.fromContentDisposition(cd_header) orelse {
                    return f.fail(f.location_tok, try eb.printString(
                        "unsupported Content-Disposition header value: '{s}' for Content-Type=application/octet-stream",
                        .{cd_header},
                    ));
                };
            }

            // Finally, the path from the URI is used.
            break :ft FileType.fromPath(uri_path) orelse {
                return f.fail(f.location_tok, try eb.printString(
                    "unknown file type: '{s}'",
                    .{uri_path},
                ));
            };
        },

        .git => .git_pack,

        .dir => |dir| {
            f.recursiveDirectoryCopy(dir, tmp_directory.handle) catch |err| {
                return f.fail(f.location_tok, try eb.printString(
                    "unable to copy directory '{s}': {s}",
                    .{ uri_path, @errorName(err) },
                ));
            };
            return .{};
        },
    };

    switch (file_type) {
        .tar => return try unpackTarball(f, tmp_directory.handle, resource.reader()),
        .@"tar.gz" => {
            const reader = resource.reader();
            var br = std.io.bufferedReaderSize(std.crypto.tls.max_ciphertext_record_len, reader);
            var dcp = std.compress.gzip.decompressor(br.reader());
            return try unpackTarball(f, tmp_directory.handle, dcp.reader());
        },
        .@"tar.xz" => {
            const gpa = f.arena.child_allocator;
            const reader = resource.reader();
            var br = std.io.bufferedReaderSize(std.crypto.tls.max_ciphertext_record_len, reader);
            var dcp = std.compress.xz.decompress(gpa, br.reader()) catch |err| {
                return f.fail(f.location_tok, try eb.printString(
                    "unable to decompress tarball: {s}",
                    .{@errorName(err)},
                ));
            };
            defer dcp.deinit();
            return try unpackTarball(f, tmp_directory.handle, dcp.reader());
        },
        .@"tar.zst" => {
            const window_size = std.compress.zstd.DecompressorOptions.default_window_buffer_len;
            const window_buffer = try f.arena.allocator().create([window_size]u8);
            const reader = resource.reader();
            var br = std.io.bufferedReaderSize(std.crypto.tls.max_ciphertext_record_len, reader);
            var dcp = std.compress.zstd.decompressor(br.reader(), .{
                .window_buffer = window_buffer,
            });
            return try unpackTarball(f, tmp_directory.handle, dcp.reader());
        },
        .git_pack => return unpackGitPack(f, tmp_directory.handle, &resource.git) catch |err| switch (err) {
            error.FetchFailed => return error.FetchFailed,
            error.OutOfMemory => return error.OutOfMemory,
            else => |e| return f.fail(f.location_tok, try eb.printString(
                "unable to unpack git files: {s}",
                .{@errorName(e)},
            )),
        },
        .zip => return try unzip(f, tmp_directory.handle, resource.reader()),
    }
}

fn unpackTarball(f: *Fetch, out_dir: fs.Dir, reader: anytype) RunError!UnpackResult {
    const eb = &f.error_bundle;
    const arena = f.arena.allocator();

    var diagnostics: std.tar.Diagnostics = .{ .allocator = arena };

    std.tar.pipeToFileSystem(out_dir, reader, .{
        .diagnostics = &diagnostics,
        .strip_components = 0,
        .mode_mode = .ignore,
        .exclude_empty_directories = true,
    }) catch |err| return f.fail(f.location_tok, try eb.printString(
        "unable to unpack tarball to temporary directory: {s}",
        .{@errorName(err)},
    ));

    var res: UnpackResult = .{ .root_dir = diagnostics.root_dir };
    if (diagnostics.errors.items.len > 0) {
        try res.allocErrors(arena, diagnostics.errors.items.len, "unable to unpack tarball");
        for (diagnostics.errors.items) |item| {
            switch (item) {
                .unable_to_create_file => |i| res.unableToCreateFile(stripRoot(i.file_name, res.root_dir), i.code),
                .unable_to_create_sym_link => |i| res.unableToCreateSymLink(stripRoot(i.file_name, res.root_dir), i.link_name, i.code),
                .unsupported_file_type => |i| res.unsupportedFileType(stripRoot(i.file_name, res.root_dir), @intFromEnum(i.file_type)),
                .components_outside_stripped_prefix => unreachable, // unreachable with strip_components = 0
            }
        }
    }
    return res;
}

fn unzip(f: *Fetch, out_dir: fs.Dir, reader: anytype) RunError!UnpackResult {
    // We write the entire contents to a file first because zip files
    // must be processed back to front and they could be too large to
    // load into memory.

    const cache_root = f.job_queue.global_cache;

    // TODO: the downside of this solution is if we get a failure/crash/oom/power out
    //       during this process, we leave behind a zip file that would be
    //       difficult to know if/when it can be cleaned up.
    //       Might be worth it to use a mechanism that enables other processes
    //       to see if the owning process of a file is still alive (on linux this
    //       can be done with file locks).
    //       Coupled with this mechansism, we could also use slots (i.e. zig-cache/tmp/0,
    //       zig-cache/tmp/1, etc) which would mean that subsequent runs would
    //       automatically clean up old dead files.
    //       This could all be done with a simple TmpFile abstraction.
    const prefix = "tmp/";
    const suffix = ".zip";

    const random_bytes_count = 20;
    const random_path_len = comptime std.fs.base64_encoder.calcSize(random_bytes_count);
    var zip_path: [prefix.len + random_path_len + suffix.len]u8 = undefined;
    @memcpy(zip_path[0..prefix.len], prefix);
    @memcpy(zip_path[prefix.len + random_path_len ..], suffix);
    {
        var random_bytes: [random_bytes_count]u8 = undefined;
        std.crypto.random.bytes(&random_bytes);
        _ = std.fs.base64_encoder.encode(
            zip_path[prefix.len..][0..random_path_len],
            &random_bytes,
        );
    }

    defer cache_root.handle.deleteFile(&zip_path) catch {};

    const eb = &f.error_bundle;

    {
        var zip_file = cache_root.handle.createFile(
            &zip_path,
            .{},
        ) catch |err| return f.fail(f.location_tok, try eb.printString(
            "failed to create tmp zip file: {s}",
            .{@errorName(err)},
        ));
        defer zip_file.close();
        var buf: [4096]u8 = undefined;
        while (true) {
            const len = reader.readAll(&buf) catch |err| return f.fail(f.location_tok, try eb.printString(
                "read zip stream failed: {s}",
                .{@errorName(err)},
            ));
            if (len == 0) break;
            zip_file.writer().writeAll(buf[0..len]) catch |err| return f.fail(f.location_tok, try eb.printString(
                "write temporary zip file failed: {s}",
                .{@errorName(err)},
            ));
        }
    }

    var diagnostics: std.zip.Diagnostics = .{ .allocator = f.arena.allocator() };
    // no need to deinit since we are using an arena allocator

    {
        var zip_file = cache_root.handle.openFile(
            &zip_path,
            .{},
        ) catch |err| return f.fail(f.location_tok, try eb.printString(
            "failed to open temporary zip file: {s}",
            .{@errorName(err)},
        ));
        defer zip_file.close();

        std.zip.extract(out_dir, zip_file.seekableStream(), .{
            .allow_backslashes = true,
            .diagnostics = &diagnostics,
        }) catch |err| return f.fail(f.location_tok, try eb.printString(
            "zip extract failed: {s}",
            .{@errorName(err)},
        ));
    }

    cache_root.handle.deleteFile(&zip_path) catch |err| return f.fail(f.location_tok, try eb.printString(
        "delete temporary zip failed: {s}",
        .{@errorName(err)},
    ));

    const res: UnpackResult = .{ .root_dir = diagnostics.root_dir };
    return res;
}

fn unpackGitPack(f: *Fetch, out_dir: fs.Dir, resource: *Resource.Git) anyerror!UnpackResult {
    const arena = f.arena.allocator();
    const gpa = f.arena.child_allocator;
    const object_format: git.Oid.Format = resource.want_oid;

    var res: UnpackResult = .{};
    // The .git directory is used to store the packfile and associated index, but
    // we do not attempt to replicate the exact structure of a real .git
    // directory, since that isn't relevant for fetching a package.
    {
        var pack_dir = try out_dir.makeOpenPath(".git", .{});
        defer pack_dir.close();
        var pack_file = try pack_dir.createFile("pkg.pack", .{ .read = true });
        defer pack_file.close();
        var fifo = std.fifo.LinearFifo(u8, .{ .Static = 4096 }).init();
        try fifo.pump(resource.fetch_stream.reader(), pack_file.writer());
        try pack_file.sync();

        var index_file = try pack_dir.createFile("pkg.idx", .{ .read = true });
        defer index_file.close();
        {
            const index_prog_node = f.prog_node.start("Index pack", 0);
            defer index_prog_node.end();
            var index_buffered_writer = std.io.bufferedWriter(index_file.writer());
            try git.indexPack(gpa, object_format, pack_file, index_buffered_writer.writer());
            try index_buffered_writer.flush();
            try index_file.sync();
        }

        {
            const checkout_prog_node = f.prog_node.start("Checkout", 0);
            defer checkout_prog_node.end();
            var repository = try git.Repository.init(gpa, object_format, pack_file, index_file);
            defer repository.deinit();
            var diagnostics: git.Diagnostics = .{ .allocator = arena };
            try repository.checkout(out_dir, resource.want_oid, &diagnostics);

            if (diagnostics.errors.items.len > 0) {
                try res.allocErrors(arena, diagnostics.errors.items.len, "unable to unpack packfile");
                for (diagnostics.errors.items) |item| {
                    switch (item) {
                        .unable_to_create_file => |i| res.unableToCreateFile(i.file_name, i.code),
                        .unable_to_create_sym_link => |i| res.unableToCreateSymLink(i.file_name, i.link_name, i.code),
                    }
                }
            }
        }
    }

    try out_dir.deleteTree(".git");
    return res;
}

fn recursiveDirectoryCopy(f: *Fetch, dir: fs.Dir, tmp_dir: fs.Dir) anyerror!void {
    const gpa = f.arena.child_allocator;
    // Recursive directory copy.
    var it = try dir.walk(gpa);
    defer it.deinit();
    while (try it.next()) |entry| {
        switch (entry.kind) {
            .directory => {}, // omit empty directories
            .file => {
                dir.copyFile(
                    entry.path,
                    tmp_dir,
                    entry.path,
                    .{},
                ) catch |err| switch (err) {
                    error.FileNotFound => {
                        if (fs.path.dirname(entry.path)) |dirname| try tmp_dir.makePath(dirname);
                        try dir.copyFile(entry.path, tmp_dir, entry.path, .{});
                    },
                    else => |e| return e,
                };
            },
            .sym_link => {
                var buf: [fs.max_path_bytes]u8 = undefined;
                const link_name = try dir.readLink(entry.path, &buf);
                // TODO: if this would create a symlink to outside
                // the destination directory, fail with an error instead.
                tmp_dir.symLink(link_name, entry.path, .{}) catch |err| switch (err) {
                    error.FileNotFound => {
                        if (fs.path.dirname(entry.path)) |dirname| try tmp_dir.makePath(dirname);
                        try tmp_dir.symLink(link_name, entry.path, .{});
                    },
                    else => |e| return e,
                };
            },
            else => return error.IllegalFileTypeInPackage,
        }
    }
}

pub fn renameTmpIntoCache(cache_dir: fs.Dir, tmp_dir_sub_path: []const u8, dest_dir_sub_path: []const u8) !void {
    assert(dest_dir_sub_path[1] == fs.path.sep);
    var handled_missing_dir = false;
    while (true) {
        cache_dir.rename(tmp_dir_sub_path, dest_dir_sub_path) catch |err| switch (err) {
            error.FileNotFound => {
                if (handled_missing_dir) return err;
                cache_dir.makeDir(dest_dir_sub_path[0..1]) catch |mkd_err| switch (mkd_err) {
                    error.PathAlreadyExists => handled_missing_dir = true,
                    else => |e| return e,
                };
                continue;
            },
            error.PathAlreadyExists, error.AccessDenied => {
                // Package has been already downloaded and may already be in use on the system.
                cache_dir.deleteTree(tmp_dir_sub_path) catch {
                    // Garbage files leftover in zig-cache/tmp/ is, as they say
                    // on Star Trek, "operating within normal parameters".
                };
            },
            else => |e| return e,
        };
        break;
    }
}

const ComputedHash = struct {
    digest: Package.Hash.Digest,
    total_size: u64,
};

/// Assumes that files not included in the package have already been filtered
/// prior to calling this function. This ensures that files not protected by
/// the hash are not present on the file system. Empty directories are *not
/// hashed* and must not be present on the file system when calling this
/// function.
fn computeHash(f: *Fetch, pkg_path: Cache.Path, filter: Filter) RunError!ComputedHash {
    // All the path name strings need to be in memory for sorting.
    const arena = f.arena.allocator();
    const gpa = f.arena.child_allocator;
    const eb = &f.error_bundle;
    const thread_pool = f.job_queue.thread_pool;
    const root_dir = pkg_path.root_dir.handle;

    // Collect all files, recursively, then sort.
    var all_files = std.ArrayList(*HashedFile).init(gpa);
    defer all_files.deinit();

    var deleted_files = std.ArrayList(*DeletedFile).init(gpa);
    defer deleted_files.deinit();

    // Track directories which had any files deleted from them so that empty directories
    // can be deleted.
    var sus_dirs: std.StringArrayHashMapUnmanaged(void) = .empty;
    defer sus_dirs.deinit(gpa);

    var walker = try root_dir.walk(gpa);
    defer walker.deinit();

    // Total number of bytes of file contents included in the package.
    var total_size: u64 = 0;

    {
        // The final hash will be a hash of each file hashed independently. This
        // allows hashing in parallel.
        var wait_group: WaitGroup = .{};
        // `computeHash` is called from a worker thread so there must not be
        // any waiting without working or a deadlock could occur.
        defer thread_pool.waitAndWork(&wait_group);

        while (walker.next() catch |err| {
            try eb.addRootErrorMessage(.{ .msg = try eb.printString(
                "unable to walk temporary directory '{}': {s}",
                .{ pkg_path, @errorName(err) },
            ) });
            return error.FetchFailed;
        }) |entry| {
            if (entry.kind == .directory) continue;

            const entry_pkg_path = stripRoot(entry.path, pkg_path.sub_path);
            if (!filter.includePath(entry_pkg_path)) {
                // Delete instead of including in hash calculation.
                const fs_path = try arena.dupe(u8, entry.path);

                // Also track the parent directory in case it becomes empty.
                if (fs.path.dirname(fs_path)) |parent|
                    try sus_dirs.put(gpa, parent, {});

                const deleted_file = try arena.create(DeletedFile);
                deleted_file.* = .{
                    .fs_path = fs_path,
                    .failure = undefined, // to be populated by the worker
                };
                thread_pool.spawnWg(&wait_group, workerDeleteFile, .{ root_dir, deleted_file });
                try deleted_files.append(deleted_file);
                continue;
            }

            const kind: HashedFile.Kind = switch (entry.kind) {
                .directory => unreachable,
                .file => .file,
                .sym_link => .link,
                else => return f.fail(f.location_tok, try eb.printString(
                    "package contains '{s}' which has illegal file type '{s}'",
                    .{ entry.path, @tagName(entry.kind) },
                )),
            };

            if (std.mem.eql(u8, entry_pkg_path, Package.build_zig_basename))
                f.has_build_zig = true;

            const fs_path = try arena.dupe(u8, entry.path);
            const hashed_file = try arena.create(HashedFile);
            hashed_file.* = .{
                .fs_path = fs_path,
                .normalized_path = try normalizePathAlloc(arena, entry_pkg_path),
                .kind = kind,
                .hash = undefined, // to be populated by the worker
                .failure = undefined, // to be populated by the worker
                .size = undefined, // to be populated by the worker
            };
            thread_pool.spawnWg(&wait_group, workerHashFile, .{ root_dir, hashed_file });
            try all_files.append(hashed_file);
        }
    }

    {
        // Sort by length, descending, so that child directories get removed first.
        sus_dirs.sortUnstable(@as(struct {
            keys: []const []const u8,
            pub fn lessThan(ctx: @This(), a_index: usize, b_index: usize) bool {
                return ctx.keys[b_index].len < ctx.keys[a_index].len;
            }
        }, .{ .keys = sus_dirs.keys() }));

        // During this loop, more entries will be added, so we must loop by index.
        var i: usize = 0;
        while (i < sus_dirs.count()) : (i += 1) {
            const sus_dir = sus_dirs.keys()[i];
            root_dir.deleteDir(sus_dir) catch |err| switch (err) {
                error.DirNotEmpty => continue,
                error.FileNotFound => continue,
                else => |e| {
                    try eb.addRootErrorMessage(.{ .msg = try eb.printString(
                        "unable to delete empty directory '{s}': {s}",
                        .{ sus_dir, @errorName(e) },
                    ) });
                    return error.FetchFailed;
                },
            };
            if (fs.path.dirname(sus_dir)) |parent| {
                try sus_dirs.put(gpa, parent, {});
            }
        }
    }

    std.mem.sortUnstable(*HashedFile, all_files.items, {}, HashedFile.lessThan);

    var hasher = Package.Hash.Algo.init(.{});
    var any_failures = false;
    for (all_files.items) |hashed_file| {
        hashed_file.failure catch |err| {
            any_failures = true;
            try eb.addRootErrorMessage(.{
                .msg = try eb.printString("unable to hash '{s}': {s}", .{
                    hashed_file.fs_path, @errorName(err),
                }),
            });
        };
        hasher.update(&hashed_file.hash);
        total_size += hashed_file.size;
    }
    for (deleted_files.items) |deleted_file| {
        deleted_file.failure catch |err| {
            any_failures = true;
            try eb.addRootErrorMessage(.{
                .msg = try eb.printString("failed to delete excluded path '{s}' from package: {s}", .{
                    deleted_file.fs_path, @errorName(err),
                }),
            });
        };
    }

    if (any_failures) return error.FetchFailed;

    if (f.job_queue.debug_hash) {
        assert(!f.job_queue.recursive);
        // Print something to stdout that can be text diffed to figure out why
        // the package hash is different.
        dumpHashInfo(all_files.items) catch |err| {
            std.debug.print("unable to write to stdout: {s}\n", .{@errorName(err)});
            std.process.exit(1);
        };
    }

    return .{
        .digest = hasher.finalResult(),
        .total_size = total_size,
    };
}

fn dumpHashInfo(all_files: []const *const HashedFile) !void {
    const stdout = std.io.getStdOut();
    var bw = std.io.bufferedWriter(stdout.writer());
    const w = bw.writer();

    for (all_files) |hashed_file| {
        try w.print("{s}: {s}: {s}\n", .{
            @tagName(hashed_file.kind),
            std.fmt.fmtSliceHexLower(&hashed_file.hash),
            hashed_file.normalized_path,
        });
    }

    try bw.flush();
}

fn workerHashFile(dir: fs.Dir, hashed_file: *HashedFile) void {
    hashed_file.failure = hashFileFallible(dir, hashed_file);
}

fn workerDeleteFile(dir: fs.Dir, deleted_file: *DeletedFile) void {
    deleted_file.failure = deleteFileFallible(dir, deleted_file);
}

fn hashFileFallible(dir: fs.Dir, hashed_file: *HashedFile) HashedFile.Error!void {
    var buf: [8000]u8 = undefined;
    var hasher = Package.Hash.Algo.init(.{});
    hasher.update(hashed_file.normalized_path);
    var file_size: u64 = 0;

    switch (hashed_file.kind) {
        .file => {
            var file = try dir.openFile(hashed_file.fs_path, .{});
            defer file.close();
            // Hard-coded false executable bit: https://github.com/ziglang/zig/issues/17463
            hasher.update(&.{ 0, 0 });
            var file_header: FileHeader = .{};
            while (true) {
                const bytes_read = try file.read(&buf);
                if (bytes_read == 0) break;
                file_size += bytes_read;
                hasher.update(buf[0..bytes_read]);
                file_header.update(buf[0..bytes_read]);
            }
            if (file_header.isExecutable()) {
                try setExecutable(file);
            }
        },
        .link => {
            const link_name = try dir.readLink(hashed_file.fs_path, &buf);
            if (fs.path.sep != canonical_sep) {
                // Package hashes are intended to be consistent across
                // platforms which means we must normalize path separators
                // inside symlinks.
                normalizePath(link_name);
            }
            hasher.update(link_name);
        },
    }
    hasher.final(&hashed_file.hash);
    hashed_file.size = file_size;
}

fn deleteFileFallible(dir: fs.Dir, deleted_file: *DeletedFile) DeletedFile.Error!void {
    try dir.deleteFile(deleted_file.fs_path);
}

fn setExecutable(file: fs.File) !void {
    if (!std.fs.has_executable_bit) return;

    const S = std.posix.S;
    const mode = fs.File.default_mode | S.IXUSR | S.IXGRP | S.IXOTH;
    try file.chmod(mode);
}

const DeletedFile = struct {
    fs_path: []const u8,
    failure: Error!void,

    const Error =
        fs.Dir.DeleteFileError ||
        fs.Dir.DeleteDirError;
};

const HashedFile = struct {
    fs_path: []const u8,
    normalized_path: []const u8,
    hash: Package.Hash.Digest,
    failure: Error!void,
    kind: Kind,
    size: u64,

    const Error =
        fs.File.OpenError ||
        fs.File.ReadError ||
        fs.File.StatError ||
        fs.File.ChmodError ||
        fs.Dir.ReadLinkError;

    const Kind = enum { file, link };

    fn lessThan(context: void, lhs: *const HashedFile, rhs: *const HashedFile) bool {
        _ = context;
        return std.mem.lessThan(u8, lhs.normalized_path, rhs.normalized_path);
    }
};

/// Strips root directory name from file system path.
fn stripRoot(fs_path: []const u8, root_dir: []const u8) []const u8 {
    if (root_dir.len == 0 or fs_path.len <= root_dir.len) return fs_path;

    if (std.mem.eql(u8, fs_path[0..root_dir.len], root_dir) and fs.path.isSep(fs_path[root_dir.len])) {
        return fs_path[root_dir.len + 1 ..];
    }

    return fs_path;
}

/// Make a file system path identical independently of operating system path inconsistencies.
/// This converts backslashes into forward slashes.
fn normalizePathAlloc(arena: Allocator, pkg_path: []const u8) ![]const u8 {
    const normalized = try arena.dupe(u8, pkg_path);
    if (fs.path.sep == canonical_sep) return normalized;
    normalizePath(normalized);
    return normalized;
}

const canonical_sep = fs.path.sep_posix;

fn normalizePath(bytes: []u8) void {
    assert(fs.path.sep != canonical_sep);
    std.mem.replaceScalar(u8, bytes, fs.path.sep, canonical_sep);
}

const Filter = struct {
    include_paths: std.StringArrayHashMapUnmanaged(void) = .empty,

    /// sub_path is relative to the package root.
    pub fn includePath(self: Filter, sub_path: []const u8) bool {
        if (self.include_paths.count() == 0) return true;
        if (self.include_paths.contains("")) return true;
        if (self.include_paths.contains(".")) return true;
        if (self.include_paths.contains(sub_path)) return true;

        // Check if any included paths are parent directories of sub_path.
        var dirname = sub_path;
        while (std.fs.path.dirname(dirname)) |next_dirname| {
            if (self.include_paths.contains(next_dirname)) return true;
            dirname = next_dirname;
        }

        return false;
    }

    test includePath {
        const gpa = std.testing.allocator;
        var filter: Filter = .{};
        defer filter.include_paths.deinit(gpa);

        try filter.include_paths.put(gpa, "src", {});
        try std.testing.expect(filter.includePath("src/core/unix/SDL_poll.c"));
        try std.testing.expect(!filter.includePath(".gitignore"));
    }
};

pub fn depDigest(pkg_root: Cache.Path, cache_root: Cache.Directory, dep: Manifest.Dependency) ?Package.Hash {
    if (dep.hash) |h| return .fromSlice(h);

    switch (dep.location) {
        .url => return null,
        .path => |rel_path| {
            var buf: [fs.max_path_bytes]u8 = undefined;
            var fba = std.heap.FixedBufferAllocator.init(&buf);
            const new_root = pkg_root.resolvePosix(fba.allocator(), rel_path) catch
                return null;
            return relativePathDigest(new_root, cache_root);
        },
    }
}

const builtin = @import("builtin");
const std = @import("std");
const fs = std.fs;
const assert = std.debug.assert;
const ascii = std.ascii;
const Allocator = std.mem.Allocator;
const Cache = std.Build.Cache;
const ThreadPool = std.Thread.Pool;
const WaitGroup = std.Thread.WaitGroup;
const Fetch = @This();
const git = @import("Fetch/git.zig");
const Package = @import("../Package.zig");
const Manifest = Package.Manifest;
const ErrorBundle = std.zig.ErrorBundle;
const native_os = builtin.os.tag;

test {
    _ = Filter;
    _ = FileType;
    _ = UnpackResult;
}

// Detects executable header: ELF or Macho-O magic header or shebang line.
const FileHeader = struct {
    header: [4]u8 = undefined,
    bytes_read: usize = 0,

    pub fn update(self: *FileHeader, buf: []const u8) void {
        if (self.bytes_read >= self.header.len) return;
        const n = @min(self.header.len - self.bytes_read, buf.len);
        @memcpy(self.header[self.bytes_read..][0..n], buf[0..n]);
        self.bytes_read += n;
    }

    fn isScript(self: *FileHeader) bool {
        const shebang = "#!";
        return std.mem.eql(u8, self.header[0..@min(self.bytes_read, shebang.len)], shebang);
    }

    fn isElf(self: *FileHeader) bool {
        const elf_magic = std.elf.MAGIC;
        return std.mem.eql(u8, self.header[0..@min(self.bytes_read, elf_magic.len)], elf_magic);
    }

    fn isMachO(self: *FileHeader) bool {
        if (self.bytes_read < 4) return false;
        const magic_number = std.mem.readInt(u32, &self.header, builtin.cpu.arch.endian());
        return magic_number == std.macho.MH_MAGIC or
            magic_number == std.macho.MH_MAGIC_64 or
            magic_number == std.macho.FAT_MAGIC or
            magic_number == std.macho.FAT_MAGIC_64 or
            magic_number == std.macho.MH_CIGAM or
            magic_number == std.macho.MH_CIGAM_64 or
            magic_number == std.macho.FAT_CIGAM or
            magic_number == std.macho.FAT_CIGAM_64;
    }

    pub fn isExecutable(self: *FileHeader) bool {
        return self.isScript() or self.isElf() or self.isMachO();
    }
};

test FileHeader {
    var h: FileHeader = .{};
    try std.testing.expect(!h.isExecutable());

    const elf_magic = std.elf.MAGIC;
    h.update(elf_magic[0..2]);
    try std.testing.expect(!h.isExecutable());
    h.update(elf_magic[2..4]);
    try std.testing.expect(h.isExecutable());

    h.update(elf_magic[2..4]);
    try std.testing.expect(h.isExecutable());

    const macho64_magic_bytes = [_]u8{ 0xCF, 0xFA, 0xED, 0xFE };
    h.bytes_read = 0;
    h.update(&macho64_magic_bytes);
    try std.testing.expect(h.isExecutable());

    const macho64_cigam_bytes = [_]u8{ 0xFE, 0xED, 0xFA, 0xCF };
    h.bytes_read = 0;
    h.update(&macho64_cigam_bytes);
    try std.testing.expect(h.isExecutable());
}

// Result of the `unpackResource` operation. Enables collecting errors from
// tar/git diagnostic, filtering that errors by manifest inclusion rules and
// emitting remaining errors to an `ErrorBundle`.
const UnpackResult = struct {
    errors: []Error = undefined,
    errors_count: usize = 0,
    root_error_message: []const u8 = "",

    // A non empty value means that the package contents are inside a
    // sub-directory indicated by the named path.
    root_dir: []const u8 = "",

    const Error = union(enum) {
        unable_to_create_sym_link: struct {
            code: anyerror,
            file_name: []const u8,
            link_name: []const u8,
        },
        unable_to_create_file: struct {
            code: anyerror,
            file_name: []const u8,
        },
        unsupported_file_type: struct {
            file_name: []const u8,
            file_type: u8,
        },

        fn excluded(self: Error, filter: Filter) bool {
            const file_name = switch (self) {
                .unable_to_create_file => |info| info.file_name,
                .unable_to_create_sym_link => |info| info.file_name,
                .unsupported_file_type => |info| info.file_name,
            };
            return !filter.includePath(file_name);
        }
    };

    fn allocErrors(self: *UnpackResult, arena: std.mem.Allocator, n: usize, root_error_message: []const u8) !void {
        self.root_error_message = try arena.dupe(u8, root_error_message);
        self.errors = try arena.alloc(UnpackResult.Error, n);
    }

    fn hasErrors(self: *UnpackResult) bool {
        return self.errors_count > 0;
    }

    fn unableToCreateFile(self: *UnpackResult, file_name: []const u8, err: anyerror) void {
        self.errors[self.errors_count] = .{ .unable_to_create_file = .{
            .code = err,
            .file_name = file_name,
        } };
        self.errors_count += 1;
    }

    fn unableToCreateSymLink(self: *UnpackResult, file_name: []const u8, link_name: []const u8, err: anyerror) void {
        self.errors[self.errors_count] = .{ .unable_to_create_sym_link = .{
            .code = err,
            .file_name = file_name,
            .link_name = link_name,
        } };
        self.errors_count += 1;
    }

    fn unsupportedFileType(self: *UnpackResult, file_name: []const u8, file_type: u8) void {
        self.errors[self.errors_count] = .{ .unsupported_file_type = .{
            .file_name = file_name,
            .file_type = file_type,
        } };
        self.errors_count += 1;
    }

    fn validate(self: *UnpackResult, f: *Fetch, filter: Filter) !void {
        if (self.errors_count == 0) return;

        var unfiltered_errors: u32 = 0;
        for (self.errors) |item| {
            if (item.excluded(filter)) continue;
            unfiltered_errors += 1;
        }
        if (unfiltered_errors == 0) return;

        // Emmit errors to an `ErrorBundle`.
        const eb = &f.error_bundle;
        try eb.addRootErrorMessage(.{
            .msg = try eb.addString(self.root_error_message),
            .src_loc = try f.srcLoc(f.location_tok),
            .notes_len = unfiltered_errors,
        });
        var note_i: u32 = try eb.reserveNotes(unfiltered_errors);
        for (self.errors) |item| {
            if (item.excluded(filter)) continue;
            switch (item) {
                .unable_to_create_sym_link => |info| {
                    eb.extra.items[note_i] = @intFromEnum(try eb.addErrorMessage(.{
                        .msg = try eb.printString("unable to create symlink from '{s}' to '{s}': {s}", .{
                            info.file_name, info.link_name, @errorName(info.code),
                        }),
                    }));
                },
                .unable_to_create_file => |info| {
                    eb.extra.items[note_i] = @intFromEnum(try eb.addErrorMessage(.{
                        .msg = try eb.printString("unable to create file '{s}': {s}", .{
                            info.file_name, @errorName(info.code),
                        }),
                    }));
                },
                .unsupported_file_type => |info| {
                    eb.extra.items[note_i] = @intFromEnum(try eb.addErrorMessage(.{
                        .msg = try eb.printString("file '{s}' has unsupported type '{c}'", .{
                            info.file_name, info.file_type,
                        }),
                    }));
                },
            }
            note_i += 1;
        }

        return error.FetchFailed;
    }

    test validate {
        const gpa = std.testing.allocator;
        var arena_instance = std.heap.ArenaAllocator.init(gpa);
        defer arena_instance.deinit();
        const arena = arena_instance.allocator();

        // fill UnpackResult with errors
        var res: UnpackResult = .{};
        try res.allocErrors(arena, 4, "unable to unpack");
        try std.testing.expectEqual(0, res.errors_count);
        res.unableToCreateFile("dir1/file1", error.File1);
        res.unableToCreateSymLink("dir2/file2", "filename", error.SymlinkError);
        res.unableToCreateFile("dir1/file3", error.File3);
        res.unsupportedFileType("dir2/file4", 'x');
        try std.testing.expectEqual(4, res.errors_count);

        // create filter, includes dir2, excludes dir1
        var filter: Filter = .{};
        try filter.include_paths.put(arena, "dir2", {});

        // init Fetch
        var fetch: Fetch = undefined;
        fetch.parent_manifest_ast = null;
        fetch.location_tok = 0;
        try fetch.error_bundle.init(gpa);
        defer fetch.error_bundle.deinit();

        // validate errors with filter
        try std.testing.expectError(error.FetchFailed, res.validate(&fetch, filter));

        // output errors to string
        var errors = try fetch.error_bundle.toOwnedBundle("");
        defer errors.deinit(gpa);
        var out = std.ArrayList(u8).init(gpa);
        defer out.deinit();
        try errors.renderToWriter(.{ .ttyconf = .no_color }, out.writer());
        try std.testing.expectEqualStrings(
            \\error: unable to unpack
            \\    note: unable to create symlink from 'dir2/file2' to 'filename': SymlinkError
            \\    note: file 'dir2/file4' has unsupported type 'x'
            \\
        , out.items);
    }
};

test "zip" {
    const gpa = std.testing.allocator;
    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    const test_files = [_]std.zip.testutil.File{
        .{ .name = "foo", .content = "this is just foo\n", .compression = .store },
        .{ .name = "bar", .content = "another file\n", .compression = .deflate },
    };
    {
        var zip_file = try tmp.dir.createFile("test.zip", .{});
        defer zip_file.close();
        var bw = std.io.bufferedWriter(zip_file.writer());
        var store: [test_files.len]std.zip.testutil.FileStore = undefined;
        try std.zip.testutil.writeZip(bw.writer(), &test_files, &store, .{});
        try bw.flush();
    }

    const zip_path = try std.fmt.allocPrint(gpa, ".zig-cache/tmp/{s}/test.zip", .{tmp.sub_path});
    defer gpa.free(zip_path);

    var fb: TestFetchBuilder = undefined;
    var fetch = try fb.build(gpa, tmp.dir, zip_path);
    defer fb.deinit();

    try fetch.run();

    var out = try fb.packageDir();
    defer out.close();

    try std.zip.testutil.expectFiles(&test_files, out, .{});
}

test "zip with one root folder" {
    const gpa = std.testing.allocator;
    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    const test_files = [_]std.zip.testutil.File{
        .{ .name = "the_root_folder/foo.zig", .content = "// this is foo.zig\n", .compression = .store },
        .{ .name = "the_root_folder/README.md", .content = "# The foo.zig README\n", .compression = .store },
    };
    {
        var zip_file = try tmp.dir.createFile("test.zip", .{});
        defer zip_file.close();
        var bw = std.io.bufferedWriter(zip_file.writer());
        var store: [test_files.len]std.zip.testutil.FileStore = undefined;
        try std.zip.testutil.writeZip(bw.writer(), &test_files, &store, .{});
        try bw.flush();
    }

    const zip_path = try std.fmt.allocPrint(gpa, ".zig-cache/tmp/{s}/test.zip", .{tmp.sub_path});
    defer gpa.free(zip_path);

    var fb: TestFetchBuilder = undefined;
    var fetch = try fb.build(gpa, tmp.dir, zip_path);
    defer fb.deinit();

    try fetch.run();

    var out = try fb.packageDir();
    defer out.close();

    try std.zip.testutil.expectFiles(&test_files, out, .{ .strip_prefix = "the_root_folder/" });
}

test "tarball with duplicate paths" {
    // This tarball has duplicate path 'dir1/file1' to simulate case sensitve
    // file system on any file sytstem.
    //
    //     duplicate_paths/
    //     duplicate_paths/dir1/
    //     duplicate_paths/dir1/file1
    //     duplicate_paths/dir1/file1
    //     duplicate_paths/build.zig.zon
    //     duplicate_paths/src/
    //     duplicate_paths/src/main.zig
    //     duplicate_paths/src/root.zig
    //     duplicate_paths/build.zig
    //

    const gpa = std.testing.allocator;
    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    const tarball_name = "duplicate_paths.tar.gz";
    try saveEmbedFile(tarball_name, tmp.dir);
    const tarball_path = try std.fmt.allocPrint(gpa, ".zig-cache/tmp/{s}/{s}", .{ tmp.sub_path, tarball_name });
    defer gpa.free(tarball_path);

    // Run tarball fetch, expect to fail
    var fb: TestFetchBuilder = undefined;
    var fetch = try fb.build(gpa, tmp.dir, tarball_path);
    defer fb.deinit();
    try std.testing.expectError(error.FetchFailed, fetch.run());

    try fb.expectFetchErrors(1,
        \\error: unable to unpack tarball
        \\    note: unable to create file 'dir1/file1': PathAlreadyExists
        \\
    );
}

test "tarball with excluded duplicate paths" {
    // Same as previous tarball but has build.zig.zon wich excludes 'dir1'.
    //
    //     .paths = .{
    //        "build.zig",
    //        "build.zig.zon",
    //        "src",
    //    }
    //

    const gpa = std.testing.allocator;
    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    const tarball_name = "duplicate_paths_excluded.tar.gz";
    try saveEmbedFile(tarball_name, tmp.dir);
    const tarball_path = try std.fmt.allocPrint(gpa, ".zig-cache/tmp/{s}/{s}", .{ tmp.sub_path, tarball_name });
    defer gpa.free(tarball_path);

    // Run tarball fetch, should succeed
    var fb: TestFetchBuilder = undefined;
    var fetch = try fb.build(gpa, tmp.dir, tarball_path);
    defer fb.deinit();
    try fetch.run();

    const hex_digest = Package.multiHashHexDigest(fetch.computed_hash.digest);
    try std.testing.expectEqualStrings(
        "12200bafe035cbb453dd717741b66e9f9d1e6c674069d06121dafa1b2e62eb6b22da",
        &hex_digest,
    );

    const expected_files: []const []const u8 = &.{
        "build.zig",
        "build.zig.zon",
        "src/main.zig",
        "src/root.zig",
    };
    try fb.expectPackageFiles(expected_files);
}

test "tarball without root folder" {
    // Tarball with root folder. Manifest excludes dir1 and dir2.
    //
    //    build.zig
    //    build.zig.zon
    //    dir1/
    //    dir1/file2
    //    dir1/file1
    //    dir2/
    //    dir2/file2
    //    src/
    //    src/main.zig
    //

    const gpa = std.testing.allocator;
    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    const tarball_name = "no_root.tar.gz";
    try saveEmbedFile(tarball_name, tmp.dir);
    const tarball_path = try std.fmt.allocPrint(gpa, ".zig-cache/tmp/{s}/{s}", .{ tmp.sub_path, tarball_name });
    defer gpa.free(tarball_path);

    // Run tarball fetch, should succeed
    var fb: TestFetchBuilder = undefined;
    var fetch = try fb.build(gpa, tmp.dir, tarball_path);
    defer fb.deinit();
    try fetch.run();

    const hex_digest = Package.multiHashHexDigest(fetch.computed_hash.digest);
    try std.testing.expectEqualStrings(
        "12209f939bfdcb8b501a61bb4a43124dfa1b2848adc60eec1e4624c560357562b793",
        &hex_digest,
    );

    const expected_files: []const []const u8 = &.{
        "build.zig",
        "build.zig.zon",
        "src/main.zig",
    };
    try fb.expectPackageFiles(expected_files);
}

test "set executable bit based on file content" {
    if (!std.fs.has_executable_bit) return error.SkipZigTest;
    const gpa = std.testing.allocator;
    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    const tarball_name = "executables.tar.gz";
    try saveEmbedFile(tarball_name, tmp.dir);
    const tarball_path = try std.fmt.allocPrint(gpa, ".zig-cache/tmp/{s}/{s}", .{ tmp.sub_path, tarball_name });
    defer gpa.free(tarball_path);

    // $ tar -tvf executables.tar.gz
    // drwxrwxr-x        0  executables/
    // -rwxrwxr-x      170  executables/hello
    // lrwxrwxrwx        0  executables/hello_ln -> hello
    // -rw-rw-r--        0  executables/file1
    // -rw-rw-r--       17  executables/script_with_shebang_without_exec_bit
    // -rwxrwxr-x        7  executables/script_without_shebang
    // -rwxrwxr-x       17  executables/script

    var fb: TestFetchBuilder = undefined;
    var fetch = try fb.build(gpa, tmp.dir, tarball_path);
    defer fb.deinit();

    try fetch.run();
    try std.testing.expectEqualStrings(
        "1220fecb4c06a9da8673c87fe8810e15785f1699212f01728eadce094d21effeeef3",
        &Package.multiHashHexDigest(fetch.computed_hash.digest),
    );

    var out = try fb.packageDir();
    defer out.close();
    const S = std.posix.S;
    // expect executable bit not set
    try std.testing.expect((try out.statFile("file1")).mode & S.IXUSR == 0);
    try std.testing.expect((try out.statFile("script_without_shebang")).mode & S.IXUSR == 0);
    // expect executable bit set
    try std.testing.expect((try out.statFile("hello")).mode & S.IXUSR != 0);
    try std.testing.expect((try out.statFile("script")).mode & S.IXUSR != 0);
    try std.testing.expect((try out.statFile("script_with_shebang_without_exec_bit")).mode & S.IXUSR != 0);
    try std.testing.expect((try out.statFile("hello_ln")).mode & S.IXUSR != 0);

    //
    // $ ls -al zig-cache/tmp/OCz9ovUcstDjTC_U/zig-global-cache/p/1220fecb4c06a9da8673c87fe8810e15785f1699212f01728eadce094d21effeeef3
    // -rw-rw-r-- 1     0 Apr   file1
    // -rwxrwxr-x 1   170 Apr   hello
    // lrwxrwxrwx 1     5 Apr   hello_ln -> hello
    // -rwxrwxr-x 1    17 Apr   script
    // -rw-rw-r-- 1     7 Apr   script_without_shebang
    // -rwxrwxr-x 1    17 Apr   script_with_shebang_without_exec_bit
}

fn saveEmbedFile(comptime tarball_name: []const u8, dir: fs.Dir) !void {
    //const tarball_name = "duplicate_paths_excluded.tar.gz";
    const tarball_content = @embedFile("Fetch/testdata/" ++ tarball_name);
    var tmp_file = try dir.createFile(tarball_name, .{});
    defer tmp_file.close();
    try tmp_file.writeAll(tarball_content);
}

// Builds Fetch with required dependencies, clears dependencies on deinit().
const TestFetchBuilder = struct {
    thread_pool: ThreadPool,
    http_client: std.http.Client,
    global_cache_directory: Cache.Directory,
    job_queue: Fetch.JobQueue,
    fetch: Fetch,

    fn build(
        self: *TestFetchBuilder,
        allocator: std.mem.Allocator,
        cache_parent_dir: std.fs.Dir,
        path_or_url: []const u8,
    ) !*Fetch {
        const cache_dir = try cache_parent_dir.makeOpenPath("zig-global-cache", .{});

        try self.thread_pool.init(.{ .allocator = allocator });
        self.http_client = .{ .allocator = allocator };
        self.global_cache_directory = .{ .handle = cache_dir, .path = null };

        self.job_queue = .{
            .http_client = &self.http_client,
            .thread_pool = &self.thread_pool,
            .global_cache = self.global_cache_directory,
            .recursive = false,
            .read_only = false,
            .debug_hash = false,
            .work_around_btrfs_bug = false,
            .mode = .needed,
        };

        self.fetch = .{
            .arena = std.heap.ArenaAllocator.init(allocator),
            .location = .{ .path_or_url = path_or_url },
            .location_tok = 0,
            .hash_tok = .none,
            .name_tok = 0,
            .lazy_status = .eager,
            .parent_package_root = Cache.Path{ .root_dir = Cache.Directory{ .handle = cache_dir, .path = null } },
            .parent_manifest_ast = null,
            .prog_node = std.Progress.Node.none,
            .job_queue = &self.job_queue,
            .omit_missing_hash_error = true,
            .allow_missing_paths_field = false,
            .allow_missing_fingerprint = true, // so we can keep using the old testdata .tar.gz
            .allow_name_string = true, // so we can keep using the old testdata .tar.gz
            .use_latest_commit = true,

            .package_root = undefined,
            .error_bundle = undefined,
            .manifest = null,
            .manifest_ast = undefined,
            .computed_hash = undefined,
            .has_build_zig = false,
            .oom_flag = false,
            .latest_commit = null,

            .module = null,
        };
        return &self.fetch;
    }

    fn deinit(self: *TestFetchBuilder) void {
        self.fetch.deinit();
        self.job_queue.deinit();
        self.fetch.prog_node.end();
        self.global_cache_directory.handle.close();
        self.http_client.deinit();
        self.thread_pool.deinit();
    }

    fn packageDir(self: *TestFetchBuilder) !fs.Dir {
        const root = self.fetch.package_root;
        return try root.root_dir.handle.openDir(root.sub_path, .{ .iterate = true });
    }

    // Test helper, asserts thet package dir constains expected_files.
    // expected_files must be sorted.
    fn expectPackageFiles(self: *TestFetchBuilder, expected_files: []const []const u8) !void {
        var package_dir = try self.packageDir();
        defer package_dir.close();

        var actual_files: std.ArrayListUnmanaged([]u8) = .empty;
        defer actual_files.deinit(std.testing.allocator);
        defer for (actual_files.items) |file| std.testing.allocator.free(file);
        var walker = try package_dir.walk(std.testing.allocator);
        defer walker.deinit();
        while (try walker.next()) |entry| {
            if (entry.kind != .file) continue;
            const path = try std.testing.allocator.dupe(u8, entry.path);
            errdefer std.testing.allocator.free(path);
            std.mem.replaceScalar(u8, path, std.fs.path.sep, '/');
            try actual_files.append(std.testing.allocator, path);
        }
        std.mem.sortUnstable([]u8, actual_files.items, {}, struct {
            fn lessThan(_: void, a: []u8, b: []u8) bool {
                return std.mem.lessThan(u8, a, b);
            }
        }.lessThan);

        try std.testing.expectEqual(expected_files.len, actual_files.items.len);
        for (expected_files, 0..) |file_name, i| {
            try std.testing.expectEqualStrings(file_name, actual_files.items[i]);
        }
        try std.testing.expectEqualDeep(expected_files, actual_files.items);
    }

    // Test helper, asserts that fetch has failed with `msg` error message.
    fn expectFetchErrors(self: *TestFetchBuilder, notes_len: usize, msg: []const u8) !void {
        var errors = try self.fetch.error_bundle.toOwnedBundle("");
        defer errors.deinit(std.testing.allocator);

        const em = errors.getErrorMessage(errors.getMessages()[0]);
        try std.testing.expectEqual(1, em.count);
        if (notes_len > 0) {
            try std.testing.expectEqual(notes_len, em.notes_len);
        }
        var al = std.ArrayList(u8).init(std.testing.allocator);
        defer al.deinit();
        try errors.renderToWriter(.{ .ttyconf = .no_color }, al.writer());
        try std.testing.expectEqualStrings(msg, al.items);
    }
};