feat(perf): run node-based commands in the current process

index.js

@@ -1,7 +1,10 @@
 #!/usr/bin/env node
 'use strict'
 
+const Buffer = require('safe-buffer').Buffer
+
 const child = require('./child')
+const fs = require('fs')
 const parseArgs = require('./parse-args.js')
 const path = require('path')
 const which = promisify(require('which'))
@@ -74,16 +77,7 @@ function main (argv) {
         return existing
       }
     }).then(existing => {
-      return child.runCommand(existing, argv).catch(err => {
-        if (err.isOperational && err.exitCode) {
-          // At this point, we want to treat errors from the child as if
-          // we were just running the command. That means no extra msg logging
-          process.exitCode = err.exitCode
-        } else {
-          // But if it's not just a regular child-level error, blow up normally
-          throw err
-        }
-      })
+      return execCommand(existing, argv)
     }).catch(err => {
       !argv.q && console.error(err.message)
       process.exitCode = err.exitCode || 1
@@ -182,6 +176,53 @@ function installPackages (specs, prefix, opts) {
   })
 }
 
+function execCommand (existing, argv) {
+  return checkIfNode(existing).then(isNode => {
+    if (isNode && module.constructor.runMain) {
+      // let it take over the process. This means we can skip node startup!
+      process.argv = [
+        process.argv[0], // Current node binary
+        existing // node script path
+      ].concat(argv.cmdOpts) // options for the cmd itself
+      if (!argv.noYargs) {
+        require('yargs').reset() // blow away built-up yargs crud
+      }
+      module.constructor.runMain() // ✨MAGIC✨. Sorry-not-sorry
+    } else {
+      return child.runCommand(existing, argv).catch(err => {
+        if (err.isOperational && err.exitCode) {
+          // At this point, we want to treat errors from the child as if
+          // we were just running the command. That means no extra msg logging
+          process.exitCode = err.exitCode
+        } else {
+          // But if it's not just a regular child-level error, blow up normally
+          throw err
+        }
+      })
+    }
+  })
+}
+
+function checkIfNode (existing) {
+  if (!existing || process.platform === 'win32') {
+    return Promise.resolve(false)
+  } else {
+    // NOTE: only *nix is supported for process-replacement juggling
+    const line = '#!/usr/bin/env node\n'
+    const bytecount = line.length
+    const buf = Buffer.alloc(bytecount)
+    return promisify(fs.open)(existing, 'r').then(fd => {
+      return promisify(fs.read)(fd, buf, 0, bytecount, 0).then(() => {
+        return promisify(fs.close)(fd)
+      }, err => {
+        return promisify(fs.close)(fd).then(() => { throw err })
+      })
+    }).then(() => {
+      return buf.toString('utf8') === line
+    })
+  }
+}
+
 function Y () {
   return require('./y.js')
 }

package.json

@@ -40,6 +40,7 @@
     "npm": "^5.0.3",
     "npm-package-arg": "^5.1.2",
     "rimraf": "^2.6.1",
+    "safe-buffer": "^5.1.0",
     "update-notifier": "^2.2.0",
     "which": "^1.2.14",
     "y18n": "^3.2.1",
@@ -53,7 +54,8 @@
     "which",
     "yargs",
     "dotenv",
-    "y18n"
+    "y18n",
+    "safe-buffer"
   ],
   "devDependencies": {
     "cross-env": "^5.0.1",

parse-args.js

@@ -106,6 +106,7 @@ function fastPathArgs (argv) {
     p: pkg,
     shell: false,
     install: true,
+    noYargs: true,
     npm: DEFAULT_NPM
   }
 }