Docs: Document the unstable_* options users would set

docs/API.md

@@ -64,7 +64,7 @@ Creates a Metro server based on the config and returns it. Its `processRequest`
 
 **Required options:** `entry`
 
-**Basic options:** `out`, `bundleOut`, `sourceMapOut`, `dev`, `minify`, `platform`, `sourceMap`, `sourceMapUrl`, `assets`, `onBegin`, `onProgress`, `onComplete`, `customResolverOptions`, `customTransformOptions`, `output`
+**Basic options:** `out`, `bundleOut`, `sourceMapOut`, `dev`, `minify`, `platform`, `sourceMap`, `sourceMapUrl`, `assets`, `onBegin`, `onProgress`, `onComplete`, `customResolverOptions`, `customTransformOptions`, `unstable_transformProfile`, `output`
 
 Bundles `entry` for the given `platform` (defaults to `'web'`). If `out` or `bundleOut` is given, saves the bundle to `bundleOut`, or to `out` with a `.js` extension. If `sourceMap` is set, also generates a source map. The source map will be inlined, unless `sourceMapUrl` is also defined, in which case `sourceMapUrl` is used as the bundle's `sourceMappingURL`. When saving to disk, the source map is also written to `sourceMapOut`, or to `out` with a `.map` extension. If `assets` is `true`, an array of `AssetData` will be generated and returned in the `assets` property of the result object.
 

docs/Configuration.md

@@ -493,6 +493,14 @@ In a future release of Metro, this option will be removed.
 
 :::
 
+#### `unstable_forceFullRefreshPatterns` <div class="label experimental">Experimental</div>
+
+Type: `Array<RegExp>`
+
+Modules that should trigger a full reload instead of a Fast Refresh update when they change, e.g. modules with side effects (such as style registration) that don't re-run correctly when hot reloaded. Patterns are tested against module paths relative to [`projectRoot`](#projectroot). Only applies to development bundles. Defaults to `[]`.
+
+---
+
 ### Transformer Options
 
 <!-- Keep old links to `asyncRequireModulePath` working -->
@@ -611,6 +619,18 @@ Type: `string`
 
 The URL path prefix written into each asset's `httpServerLocation`, which the app uses to request the asset. Metro's own server only serves assets under `/assets`, so with a different value you need to route those requests yourself, e.g. with [`rewriteRequestUrl`](#rewriterequesturl). Defaults to `'/assets'`.
 
+#### `unstable_allowRequireContext` <div class="label experimental">Experimental</div>
+
+Type: `boolean`
+
+Enables `require.context()`, which imports all the files in a directory that match a pattern. Defaults to `false`.
+
+#### `unstable_workerThreads` <div class="label experimental">Experimental</div>
+
+Type: `boolean`
+
+Whether to run transformer workers as worker threads instead of child processes. Defaults to `false`.
+
 #### React Native Only
 
 #### `assetPlugins`
@@ -736,6 +756,13 @@ Type: `(graph: ReadOnlyGraph, delta: DeltaResult) => mixed`
 
 A function called with the dependency graph and the changes since the previous build, each time a graph is built or updated.
 
+#### `unstable_lazilyDefineModules` <div class="label experimental">Experimental</div>
+
+Type: `boolean`
+
+Whether the default serializer defines each module lazily, on its first `require`, instead of running every `__d(...)` call at startup. This reduces startup cost and peak memory use for large bundles. Does not affect Fast Refresh updates. Defaults to `false`.
+
+---
 ### Server Options
 
 These options are used when Metro serves the content.
@@ -746,6 +773,12 @@ Type: `number`
 
 Which port to listen on. Defaults to `8081`.
 
+#### `unstable_serverRoot` <div class="label experimental">Experimental</div>
+
+Type: `?string`
+
+The directory that bundle URLs and entry files are resolved against, instead of [`projectRoot`](#projectroot). Defaults to `null` (use `projectRoot`).
+
 #### `useGlobalHotkey`
 
 Type: `boolean`

docs/GettingStarted.md

@@ -145,6 +145,7 @@ Given a configuration and a set of options that you would typically pass to a se
 * `sourceMap (boolean)`: Whether Metro should generate source maps.
 * `sourceMapOut (string)`: Where to save the source map, if `sourceMap == true`. No extension will be added.
 * `sourceMapUrl (string)`: URL where the source map can be found, written as the bundle's `sourceMappingURL`. If `sourceMap` is `true` and `sourceMapUrl` is not set, the source map is inlined into the bundle.
+* `unstable_transformProfile ('default' | 'hermes-stable' | 'hermes-canary')`: Passed to the Babel transformer, which can use it to target a specific JavaScript engine.
 
 ```js
 const config = await Metro.loadConfig();
@@ -214,6 +215,7 @@ Any JS file can be used as the root for a bundle request. The file will be looke
 * `runModule`: whether to end the bundle with the statements that run the entry point. Defaults to `true`.
 * `shallow`: whether to include only the entry module itself, without its dependencies. Defaults to `false`.
 * `sourcePaths`: how source files are referenced in the source map: as absolute file paths (`absolute`), or as URL paths on the server (`url-server`). Defaults to `absolute`.
+* `unstable_transformProfile`: passed to the Babel transformer (`default`, `hermes-stable` or `hermes-canary`). Defaults to `default`.
 * `resolver.<key>` and `transform.<key>`: [custom resolver options](./Resolution.md#customresolveroptions-string-mixed) and custom transform options, e.g. `transform.foo=bar` passes `{foo: 'bar'}` to the transformer.
 
 For instance, requesting `http://localhost:8081/foo/bar/baz.bundle?dev=true&platform=ios` will create a bundle out of `foo/bar/baz.js` for iOS in development mode.
@@ -228,7 +230,7 @@ The JavaScript transformer ([`babelTransformerPath`](./Configuration.md#babeltra
 
 ### Method `transform(module)`
 
-Mandatory method that will transform code. The object received has the module's `filename` (relative to the project root), its source code `src`, transformation `options` (e.g. `dev`, `platform`, `minify`, `projectRoot`, `customTransformOptions`), and Babel `plugins` that Metro wants applied. The returned object has to contain an `ast` key that is the AST representation of the transformed code, and may contain the Babel `metadata`. A minimal transformer only parses the code to AST:
+Mandatory method that will transform code. The object received has the module's `filename` (relative to the project root), its source code `src`, transformation `options` (e.g. `dev`, `platform`, `minify`, `projectRoot`, `customTransformOptions`, `unstable_transformProfile`), and Babel `plugins` that Metro wants applied. The returned object has to contain an `ast` key that is the AST representation of the transformed code, and may contain the Babel `metadata`. A minimal transformer only parses the code to AST:
 
 ```js
 const babylon = require('@babel/parser');