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Defining Fuchsia package information with metadata files


Fuchsia's Gerrit installation has support for custom structured metadata files. These files are designed to be:

  • human-readable and provide useful information such as the name, description and canonical URL of a package
  • machine-readable by having the files be defined using a standard format, and so can be used by automated systems for things like automatically adding reviewers to CLs or find bug components that alerting systems should file issues against

Currently, the only automated use for metadata files is for automatically adding reviewers to CLs and emailing notifications when CLs are added/submitted. These are described in the Presubmits section.

Metadata files only apply to first-party code.


Metadata files are:

The metadata message types are as follows:

syntax = "proto3";

// This proto is located at
import "google/type/date.proto";

// Monorail contains the project configuration for the Monorail issue tracker.
message Monorail {
  string project = 1;
  string component = 2;

// IssueTracker contains the project configuration for the Google
// Issue Tracker service.
message IssueTracker {
  int64 component_id = 1;

message Tracker {
  repeated Monorail monorail = 1;
  repeated IssueTracker issue_tracker = 2;
  // for_automation defines whether this tracker should be used by automated
  // processes (e.g. alerts).
  bool for_automation = 3;

message Presubmit {
  repeated string review_notify = 1;
  repeated string auto_reviewers = 2;

message Metadata {
  // name is the name of the API/Package/Program.
  string name = 1;
  string description = 2;
  // url points to some documentation/landing page.
  string url = 3;
  // Date this metadata was last reviewed by a human.
  google.type.Date last_reviewed_date = 4;
  repeated Tracker trackers = 5;
  // presubmits are used for defining presubmits.
  // The field is marked repeated for future expansion, but only
  // one message should be used.
  repeated Presubmit presubmits = 6;

Here is a fake example of a metadata file:

name: "Fuchsia source code automation"
description: "A binary for automating source code gardening tasks"
url: ""
last_reviewed_date: {
    year: 2022
    month: 1
    day: 23
trackers: {
    monorail: {
        project: "fuchsia"
        component: "EngProd"

presubmits: {
  auto_reviewers: ""

  review_notify: ""
  review_notify: ""

Multiple metadata files

To support large repositories that contain multiple distinct projects, multiple METADATA.textproto files may be used throughout the file tree. Metadata files apply to their own directory and all the directories below.


The presubmit field allows the specification of reviewers who should be automatically added to each changelist as a reviewer (auto_reviewers) and those who should be notified via email when a changelist has been uploaded/submitted (review_notify).

Here is an example hierarchy which contains multiple metadata files:

├── alice
│   ├── METADATA.textproto
│   └──
├── foo
│   └── bar
│       ├── baz
│       │   └── METADATA.textproto
│       │   └── server.go
│       └── METADATA.textproto
│       └──
├── METADATA.textproto

Reviewers specified in /METADATA.textproto are added/notified whenever there is a change to any file in the entire repository. Reviewers in /foo/bar/METADATA.textproto apply to anything in the /foo/bar directory, as well as the child directory /foo/bar/baz. Reviewers in /foo/bar/baz/METADATA.textproto only apply to files edited in the /foo/bar/baz/ directory.

Relationship to other files

Metadata files have no relationship to other files, such as OWNERS (used to specify the owners of directories) or README.fuchsia (used for defining metadata for third-party code).