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Summary:
**Summary**
`createModuleIdFactory` is already used in `metro` internally, but is currently always a fixed function.
This enables `metro.runBuild()` to be run with a custom module ID factory.
One use case: building a base bundle, on top of which other application-specific bundles could reference modules in the base. The application-specific IDs need to not conflict with those in the base bundle, and all references to modules in the base must resolve to the correct ID in the base bundle. A custom ID factory can make all this possible.
**Test plan**
<!-- Demonstrate the code is solid. Example: The exact commands you ran and their output, screenshots / videos if the pull request changes UI. -->
Using `metro.runBuild(...)` with these changes, I was able to substitute in a custom ID factory
```javascript
const fs = require('fs')
const metro = require('metro')
const baseManifestFileContents = JSON.parse(fs.readFileSync('./baseManifest.json'))
// baseManifest looks like:
// { "modules": { ...
// "react/index.js": { "id": 12 },
// "react/cjs/react.production.min.js": { "id": 13 }, ... } }
const opts = {
dev: false,
entry: 'index.js',
out: './out.bundle',
platform: 'ios',
projectRoots: ['.', 'node_modules'],
config: {
createModuleIdFactory: createModuleIdFactory(baseManifestFileContents)
}
}
metro.runBuild(opts)
// Creates a sample custom ID factory
function createModuleIdFactory(manifestFileContents) {
return function createModuleIdFactory() {
const fileToIdMap = new Map()
let nextId = manifestFileContents ? getNextIdAfterBaseManifest(manifestFileContents) : 0
return path => {
const sourcePath = path
.replace(process.cwd() + '/node_modules/', '')
.replace(process.cwd(), '.')
// If module is in the base manifest, return its ID
if (manifestFileContents && manifestFileContents.modules[sourcePath]) {
return manifestFileContents.modules[sourcePath].id
}
// Otherwise, get it from the map or create a new ID
if (!fileToIdMap.has(path)) {
fileToIdMap.set(path, nextId)
nextId += 1
}
return fileToIdMap.get(path)
}
}
function getNextIdAfterBaseManifest(manifestFileContents) {
return Object.keys(manifestFileContents.modules).reduce((id, key) => {
if (manifestFileContents.modules[key].id > id) {
return manifestFileContents.modules[key].id
}
return id
}, 0) + 1
}
}
```
With the sample module ID factory above, the output looks like the following, where defined module IDs start at a higher number to avoid the base module IDs, but may depend on modules in the base bundle (lower numbers).
```javascript
...
__d(function(r,o,t,i,n){t.exports=r.ErrorUtils},551,[]);
__d(function(n,t,o,r,u){'use strict';var e,c=t(u[0]);e=c.now?function(){return c.now()}:function(){return Date.now()},o.exports=e},552,[553]);
...
__d(function(e,t,r,s,l){'use strict'; ...},564,[18,565,27]);
...
```
Closes https://github.com/facebook/metro/pull/100
Reviewed By: mjesun
Differential Revision: D6508351
Pulled By: rafeca
fbshipit-source-id: f2cfe5c373a6c83c8ae6c526435538633a7c9c2a