[feat] Add synthetics plugin

[yoannmoinet]

Stacked on

• [internal] Change how we initialise plugins #151
  • needed to "auto enable" the plugin
• [internal] Move dev server helper #152
  • needed to factorise the local dev server implementation

Related to

• implement the build-and-test command datadog-ci#1595

What and why?

Add a Synthetics plugin.

It will be used in collaboration with datadog-ci for a new "Build and test" workflow:

1. Run datadog-ci synthetics build-and-test (name TBD).
2. datadog-ci will run the build command of the project passing BUILD_PLUGINS_S8S_PORT.
3. build-plugins will recognise BUILD_PLUGINS_S8S_PORT and will run a local dev server over the outDir of the build, with a small api /_datadog-ci_/build-status for datadog-ci to follow the build progression.
4. build's complete.
5. datadog-ci opens a tunnel.
6. datadog-ci trigger a test batch using the local assets from the build through the resourceUrlSubstitutionRegexes configuration.

More details

The local server offers two routes (in addition to the file server over the out directory):

1. /_datadog-ci_/build-status responding with:

{
    "status": "running" | "success" | "fail",
    "outDir": "/..." // Absolute path of the build's outDir.
    "publicPath": "/" // Assets' public path if available.
}

2. /_datadog-ci_/kill kills the server.

TODO

• Add documentation for s8s.

[Copilot]

Pull Request Overview

This PR introduces a new Synthetics plugin that enables the local development server for build-time testing and integrates with datadog-ci for build status reporting.

• Added Synthetics plugin implementation across various bundler plugins.
• Updated exports and factory configuration to include SyntheticsTypes.
• Introduced plugin validation, routes for build status and server shutdown, and comprehensive test coverage.

Reviewed Changes

Copilot reviewed 16 out of 20 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/published/webpack-plugin/src/index.ts	Added SyntheticsTypes export in the plugin.
packages/published/vite-plugin/src/index.ts	Added SyntheticsTypes export in the plugin.
packages/published/rspack-plugin/src/index.ts	Added SyntheticsTypes export in the plugin.
packages/published/rollup-plugin/src/index.ts	Added SyntheticsTypes export in the plugin.
packages/published/esbuild-plugin/src/index.ts	Added SyntheticsTypes export in the plugin.
packages/plugins/synthetics/src/{validate,types,index,constants}.ts	Introduced core implementation for the new Synthetics plugin.
packages/plugins/synthetics/src/index.test.ts	Added tests validating server behavior and plugin initialization.
packages/plugins/synthetics/README.md	Provided documentation for the new Synthetics plugin.
packages/factory/src/index.ts	Updated factory exports and configuration to include the Synthetics plugin.
packages/core/src/types.ts	Extended core types to support configuration for the Synthetics plugin.
README.md	Updated root documentation to include Synthetics plugin guidelines.

Files not reviewed (4)

• .github/CODEOWNERS: Language not supported
• packages/factory/package.json: Language not supported
• packages/plugins/synthetics/package.json: Language not supported
• packages/plugins/synthetics/tsconfig.json: Language not supported

Comments suppressed due to low confidence (1)

packages/plugins/synthetics/src/index.ts:66

• [nitpick] Multiple server shutdown calls (server.close, server.closeAllConnections, server.closeIdleConnections) occur in immediate succession, which may lead to unexpected behavior. Consider consolidating these calls or adding checks to ensure that the server shutdown process is idempotent.

server.close();

[Ayc0]

You need to invite etienne I think:

[yoannmoinet]

Good catch.
I'll wait for his review, see if I should instead maybe use a team (cc @etnbrd)

[etnbrd]

You should definitely use the @DataDog/synthetics-ct team, indeed.

[Ayc0]

LGTM but i'm not versed in s8s

[etnbrd]

LGTM, left a few questions, but nothing blocking.

[yoannmoinet]

Putting this on hold for now.

We'll redesign a bit the feature to have the server part running on datadog-ci's side instead of build-plugins's.

While testing with web-ui we noticed that handling sequential builds (or parallel ones even) would be very difficult to do from the build-plugins's PoV.

Instead, we'll have datadog-ci run a server and build-plugins register its builds and reporting its status to it by calling the server's API.