@carimus/metro-symlinked-deps
v1.1.0
Published
Metro bundler configuration utilities to workaround a lack of symlink support.
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@carimus/metro-symlinked-deps
Utilities to customize the metro
bundler configuration in order to workaround
its lack of support for symlinks.
The primary use case for this package is to support development on react native dependencies using yarn link
or
npm link
.
Motivation
Facebook's metro
bundler used by React Native
doesn't support symlinks which is a huge hindrance in the ability to
share code locally.
It's related and dependent on this issue with jest
since metro
uses jest-haste-map
internally to track and watch file changes.
The general process for developing on a dependency that is sharing components with the main app would be
to use yarn link
/ npm link
to symlink the dependency into the app's node_modules
. Since Metro ignores symlinks
though, it simply doesn't work out of the box with metro. There's mountains of workarounds to this that work to varying
degrees. This is the one that worked for us that we're going to re-use until it's unnecessary.
Usage
Install as a dev dependency using npm
or yarn
:
yarn add --dev @carimus/metro-symlinked-deps
Option 1: Automatic
If you don't need greater control of the resolver.blacklistRE
outside of adding additional paths or expressions to
the list, you can safely use the single applyConfigForLinkedDependencies
function which will use metro-config
's
mergeConfig
to merge in the configuration updates required for the resolver.blacklistRE
and watchFolders
.
Modify your
metro.config.js
(creating it if it doesn't exist, or converting yourmetro.config.json
tometro.config.js
if its present) to require and callapplyConfigForLinkedDependencies
on your existing configuration:const { applyConfigForLinkedDependencies, } = require('@carimus/metro-symlinked-deps'); module.exports = applyConfigForLinkedDependencies( { /* Your existing configuration, optional */ }, { /* Options to pass to applyConfigForLinkedDependencies, optional */ }, );
applyConfigForLinkedDependencies
takes the following options:
projectRoot
(string
, optional but recommended): The root of the metro bundled project. If not provided, it will be detected assuming the currentprocess.cwd()
is the project root. It's recommended to explicitly provide this to avoid detection issues.blacklistLinkedModules
(string[]
, defaults to[]
): a list of modules to blacklist/ignore if they show up in any linked dependencies'node_modules
. If you get naming collisions for certain modules, add those modules by name here and restart the bundler using--reset-cache
. A common one isreact-native
which will typically show up as a dev dependency in react native packages since it's used in tests.blacklistDirectories
(string[]
, defaults to[]
): a list of absolute or relative (toprojectRoot
) directories that should be blacklisted in addition to the directories determined viablacklistLinkedModules
.resolveBlacklistDirectoriesSymlinks
(boolean
, defaults totrue
): whether or not to resolve symlinks when processingblacklistDirectories
.additionalWatchFolders
(string[]
, defaults to[]
): a list of additional absolute paths to watch, merged directly into thewatchFolders
option.resolveAdditionalWatchFoldersSymlinks
(boolean
, defaults totrue
): whether or not to resolve symlinks when processingadditionalWatchFolders
.resolveNodeModulesAtRoot
(boolean
, defaults tofalse
): Set this totrue
to set up a Proxy forresolver.extraNodeModules
in order to ensure that all modules (even the ones required by linked dependencies or any other out-of-root watch folders) will resolve to the project root'snode_modules
directory. This is primarily useful if the linked dependencies rely on the presence of peerDependencies installed in the project root.silent
(boolean
, defaults tofalse
): Set this totrue
to suppress warning output in the bundler that shows up when linked dependencies are detected.debug
(boolean
, defaults tofalse
): Set this totrue
to log out valuable debug information like the final merged metro configuration.
Example
This setup should work for an out of the box react-native 0.60+ project:
const {
applyConfigForLinkedDependencies,
} = require('@carimus/metro-symlinked-deps');
module.exports = applyConfigForLinkedDependencies(
{
transformer: {
getTransformOptions: async () => ({
transform: {
experimentalImportSupport: false,
inlineRequires: false,
},
}),
},
},
{
projectRoot: __dirname,
blacklistLinkedModules: ['react-native'],
},
);
Option 2: Manual
TODO
Caveats
- At the time of writing the blacklist approach appears to fix the naming collision error however it requires that the developer knows which packages are in-common and that they provide that list to this package in order to generate the regular expression
- The naming collision doesn't appear to occur for ALL in-common packages. It's not clear if it also considers versions too, though that would make sense.
How it works
This is a workaround and as such it was built by incrementally addressing errors that show up.
Error #1: Module not found
Out of the box, if you try to use a symlinked dependency, you get the following error from the bundler when it first builds the bundle (not on during the transform step):
error: bundling failed: Error: Unable to resolve module `your-symlinked-module` from `/path/in/project/that/requires/the/module.js`: Module `your-symlinked-module` does not exist in the Haste module map
This might be related to https://github.com/facebook/react-native/issues/4968
To resolve try the following:
1. Clear watchman watches: `watchman watch-del-all`.
2. Delete the `node_modules` folder: `rm -rf node_modules && npm install`.
3. Reset Metro Bundler cache: `rm -rf /tmp/metro-bundler-cache-*` or `npm start -- --reset-cache`.
4. Remove haste cache: `rm -rf /tmp/haste-map-react-native-packager-*`.
Not extremely helpful but what's happening here is metro
is just outright ignoring the symlink and as such, your
module is invisible to it.
The workaround here provided by aleclarson
in
this comment on the metro
issue is to
use his home-grown get-dev-paths
package which searches node_modules
for any symlinked dependencies that
are referenced as dependencies
in your package.json
, resolve those links to their real dependencies, and then
tell metro to also watch those real directories.
Error #2: Haste module naming collision
That works great with one important caveat: if your linked dependency has any installed dependencies in its
node_modules
that are identical to any installed dependencies in the root project, you get the following error
(this error names react-native
as the common dependency).
jest-haste-map: Haste module naming collision: react-native
The following files share their name; please adjust your hasteImpl:
* <rootDir>/node_modules/react-native/package.json
* <rootDir>/../../your-symlinked-module/node_modules/react-native/package.json
When your dependency is installed legitimately (and not linked) any common dependencies are automatically deduped
during the install (during yarn install
or npm install
) and metro
(or rather jest-haste-map
) seems to rely
on this behaviour and can't identify the fact that the two packages are not conflicting with eachother and are
legitimately identical. There's unfortunately no way to tell metro
this is the case and that it should, as an
example, prefer the version of the code in the root project's node_modules
so instead we have to manually construct
a blacklist of the in-common packages in the linked dependency, construct a regular expression from that, and
hand that regular expression to the blacklistRE
option of the metro bundler's resolver
config.
TODO
- [ ] Remove
resolveNodeModulesAtRoot
and replace withnodeModulesResolutionStrategy
with three options:null
: default, don't apply anyextraNodeModules
config'peers'
: applyextraNodeModules
that will automatically detect peer dependencies in linked deps and ensure those are resolved in the project root while allowing all other dependencies to resolve naturally.'root'
: applyextraNodeModules
that will force all node modules to resolve in the project root, equivelant toresolveNodeModulesAtRoot
being set totrue
currently.