zig/lib/std/build/WriteFileStep.zig

const std = @import("../std.zig");
const build = @import("../build.zig");
const Step = build.Step;
const Builder = build.Builder;
const fs = std.fs;
const warn = std.debug.warn;
const ArrayList = std.ArrayList;

const WriteFileStep = @This();

pub const base_id = .write_file;

step: Step,
builder: *Builder,
output_dir: []const u8,
files: std.TailQueue(File),

pub const File = struct {
    source: build.GeneratedFile,
    basename: []const u8,
    bytes: []const u8,
};

pub fn init(builder: *Builder) WriteFileStep {
    return WriteFileStep{
        .builder = builder,
        .step = Step.init(.write_file, "writefile", builder.allocator, make),
        .files = .{},
        .output_dir = undefined,
    };
}

pub fn add(self: *WriteFileStep, basename: []const u8, bytes: []const u8) void {
    const node = self.builder.allocator.create(std.TailQueue(File).Node) catch unreachable;
    node.* = .{
        .data = .{
            .source = build.GeneratedFile{ .step = &self.step },
            .basename = self.builder.dupePath(basename),
            .bytes = self.builder.dupe(bytes),
        },
    };

    self.files.append(node);
}

/// Gets a file source for the given basename. If the file does not exist, returns `null`.
pub fn getFileSource(step: *WriteFileStep, basename: []const u8) ?build.FileSource {
    var it = step.files.first;
    while (it) |node| : (it = node.next) {
        if (std.mem.eql(u8, node.data.basename, basename))
            return build.FileSource{ .generated = &node.data.source };
    }
    return null;
}

fn make(step: *Step) !void {
    const self = @fieldParentPtr(WriteFileStep, "step", step);

    // The cache is used here not really as a way to speed things up - because writing
    // the data to a file would probably be very fast - but as a way to find a canonical
    // location to put build artifacts.

    // If, for example, a hard-coded path was used as the location to put WriteFileStep
    // files, then two WriteFileSteps executing in parallel might clobber each other.

    // TODO port the cache system from stage1 to zig std lib. Until then we use blake2b
    // directly and construct the path, and no "cache hit" detection happens; the files
    // are always written.
    var hash = std.crypto.hash.blake2.Blake2b384.init(.{});

    // Random bytes to make WriteFileStep unique. Refresh this with
    // new random bytes when WriteFileStep implementation is modified
    // in a non-backwards-compatible way.
    hash.update("eagVR1dYXoE7ARDP");
    {
        var it = self.files.first;
        while (it) |node| : (it = node.next) {
            hash.update(node.data.basename);
            hash.update(node.data.bytes);
            hash.update("|");
        }
    }
    var digest: [48]u8 = undefined;
    hash.final(&digest);
    var hash_basename: [64]u8 = undefined;
    _ = fs.base64_encoder.encode(&hash_basename, &digest);
    self.output_dir = try fs.path.join(self.builder.allocator, &[_][]const u8{
        self.builder.cache_root,
        "o",
        &hash_basename,
    });
    // TODO replace with something like fs.makePathAndOpenDir
    fs.cwd().makePath(self.output_dir) catch |err| {
        warn("unable to make path {s}: {s}\n", .{ self.output_dir, @errorName(err) });
        return err;
    };
    var dir = try fs.cwd().openDir(self.output_dir, .{});
    defer dir.close();
    {
        var it = self.files.first;
        while (it) |node| : (it = node.next) {
            dir.writeFile(node.data.basename, node.data.bytes) catch |err| {
                warn("unable to write {s} into {s}: {s}\n", .{
                    node.data.basename,
                    self.output_dir,
                    @errorName(err),
                });
                return err;
            };
            node.data.source.path = fs.path.join(
                self.builder.allocator,
                &[_][]const u8{ self.output_dir, node.data.basename },
            ) catch unreachable;
        }
    }
}