Add resolver.unstable_enableSymlinks and remove symlinks+watchman r…

…estriction

Summary:
**Note: this change does not mean that symlinks are respected by the resolver (yet)!**

Add `resolver.unstable_enableSymlinks` (default: `false`) option to Metro config, and pass it though to the existing `enableSymlinks` option in `metro-file-map`.

At this point this is purely for ease of testing end-to-end behaviour as we incrementally change Fast Refresh and resolution to cope with symlinks.

Removes the Jest-inherited prohibition on using `enableSymlinks` with `useWatchman`, which is no longer necessary or relevant to the new implementation.

**Bikeshed: Why under `resolver`?**
Symlink support is mostly relevant to the resolver, in that if the resolver resolves to a file through a link, that fact is transparent to the rest of Metro. Third-party solutions for symlink-based projects have focused on the resolver. The fact that 90% of the work for this solution is within `metro-file-map` is an implementation detail of in-memory resolution. That said, we'll have an opportunity to revisit this when the config is promoted from `unstable_`

Changlog: [Experimental] - Add `resolver.unstable_enableSymlinks` config for first phase of symlink support.

Reviewed By: jacdebug

Differential Revision: D42552674

fbshipit-source-id: a6cfe38973b2a484af85f4a11274c4073710a883

packages/metro-config/src/__tests__/__snapshots__/loadConfig-test.js.snap

@@ -83,6 +83,7 @@ Object {
  ],
  },
  "unstable_enablePackageExports": false,
+ "unstable_enableSymlinks": false,
  "useWatchman": true,
  },
  "serializer": Object {
@@ -259,6 +260,7 @@ Object {
  ],
  },
  "unstable_enablePackageExports": false,
+ "unstable_enableSymlinks": false,
  "useWatchman": true,
  },
  "serializer": Object {
@@ -435,6 +437,7 @@ Object {
  ],
  },
  "unstable_enablePackageExports": false,
+ "unstable_enableSymlinks": false,
  "useWatchman": true,
  },
  "serializer": Object {
@@ -611,6 +614,7 @@ Object {
  ],
  },
  "unstable_enablePackageExports": false,
+ "unstable_enableSymlinks": false,
  "useWatchman": true,
  },
  "serializer": Object {

packages/metro-config/src/configTypes.flow.js

@@ -102,6 +102,7 @@ type ResolverConfigT = {
  disableHierarchicalLookup: boolean,
  dependencyExtractor: ?string,
  emptyModulePath: string,
+ unstable_enableSymlinks: boolean,
  extraNodeModules: {[name: string]: string, ...},
  hasteImplModulePath: ?string,
  nodeModulesPaths: $ReadOnlyArray<string>,

packages/metro-config/src/defaults/index.js

@@ -39,6 +39,7 @@ const getDefaultValues = (projectRoot: ?string): ConfigT => ({
  blockList: exclusionList(),
  dependencyExtractor: undefined,
  disableHierarchicalLookup: false,
+ unstable_enableSymlinks: false,
  emptyModulePath: require.resolve(
  'metro-runtime/src/modules/empty-module.js',
  ),

packages/metro-file-map/src/__tests__/index-test.js

@@ -510,48 +510,12 @@ describe('HasteMap', () => {
  expect(deepNormalize(await hasteMap.read())).toEqual(cacheContent);
  });
 
- it('throws if both symlinks and watchman is enabled', () => {
- expect(
- () => new HasteMap({...defaultConfig, enableSymlinks: true}),
- ).toThrow(
- 'Set either `enableSymlinks` to false or `useWatchman` to false.',
- );
- expect(
- () =>
- new HasteMap({
- ...defaultConfig,
- enableSymlinks: true,
- useWatchman: true,
- }),
- ).toThrow(
- 'Set either `enableSymlinks` to false or `useWatchman` to false.',
- );
-
- expect(
- () =>
- new HasteMap({
- ...defaultConfig,
- enableSymlinks: false,
- useWatchman: true,
- }),
- ).not.toThrow();
-
- expect(
- () =>
- new HasteMap({
- ...defaultConfig,
- enableSymlinks: true,
- useWatchman: false,
- }),
- ).not.toThrow();
- });
-
  describe('builds a haste map on a fresh cache with SHA-1s', () => {
  it.each([
- // `enableSymlinks` is currently not permitted with `useWatchman`
  [false, false],
  [false, true],
  [true, false],
+ [true, true],
  ])(
  'uses watchman: %s, symlinks enabled: %s',
  async (useWatchman, enableSymlinks) => {

packages/metro-file-map/src/index.js

@@ -324,14 +324,6 @@ export default class HasteMap extends EventEmitter {
  buildParameters,
  });
 
- if (this._options.enableSymlinks && this._options.useWatchman) {
- throw new Error(
- 'metro-file-map: enableSymlinks config option was set, but ' +
- 'is incompatible with watchman.\n' +
- 'Set either `enableSymlinks` to false or `useWatchman` to false.',
- );
- }
-
  this._buildPromise = null;
  this._worker = null;
  this._startupPerfLogger?.point('constructor_end');

packages/metro/src/node-haste/DependencyGraph/createHasteMap.js

@@ -70,6 +70,7 @@ function createHasteMap(
  computeDependencies,
  computeSha1: true,
  dependencyExtractor: config.resolver.dependencyExtractor,
+ enableSymlinks: config.resolver.unstable_enableSymlinks,
  extensions: Array.from(
  new Set([
  ...config.resolver.sourceExts,