feat(prepare): allow prefetching of only specified deps

Author: zkat

lib/commands/prepare.js

@@ -1,9 +1,9 @@
 'use strict'
 
 const Prepare = module.exports = {
-  command: 'prepare',
+  command: 'prepare [packages...]',
   aliases: ['prep'],
-  describe: 'pre-fetch all dependencies',
+  describe: 'pre-fetch dependencies, or only the listed ones',
   builder (y) {
     return y.help().alias('help', 'h').options(Prepare.options)
   },
@@ -32,7 +32,8 @@ async function prepare (argv) {
       await installer({
         log (level, ...args) {
           return log[level](...args)
-        }
+        },
+        only: argv.packages
       })
     } catch (e) {
       log.error('installer', e)

lib/installer.js

@@ -43,6 +43,7 @@ class Installer {
     this.log = this.opts.log ||
       ((level, type, ...msgs) => process.emit(level, type, ...msgs))
 
+    this.onlyDeps = opts.only && new Set(opts.only)
     this.pkg = null
     this.tree = null
     this.validLockHash = false
@@ -136,6 +137,13 @@ class Installer {
     )
     await this.checkLock()
     this.tree = buildLogicalTree(this.pkg, this.pkg._shrinkwrap)
+    if (this.onlyDeps) {
+      for (const [key, dep] of this.tree.dependencies.entries()) {
+        if (!this.onlyDeps.has(key)) {
+          this.tree.delDep(dep)
+        }
+      }
+    }
     this.log('silly', 'tree', this.tree)
     this.expectedTotal = 0
     this.tree.forEach((dep, next) => {