refactor: lazily hook into child_process in asar_init (#18576)

Previously we loaded both fs and child_process and then hooked into
the returned value, relying on the module cache to keep our modifications
and give them to everyone.

Loading child_process took in excess of 20ms though so instead of loading
it and then hooking in.  We intercept all Module load requests, and when
the first one for `child_process` comes in, we wrap the appropriate methods
and then never touch it again.

lib/common/asar.js

@@ -2,9 +2,9 @@
 
 (function () {
   const asar = process._linkedBinding('atom_common_asar')
-  const assert = require('assert')
+  const v8Util = process._linkedBinding('atom_common_v8_util')
   const { Buffer } = require('buffer')
-  const childProcess = require('child_process')
+  const Module = require('module')
   const path = require('path')
   const util = require('util')
 
@@ -141,7 +141,7 @@
         error = new Error(`Invalid package ${asarPath}`)
         break
       default:
-        assert.fail(`Invalid error type "${errorType}" passed to createError.`)
+        throw new Error(`Invalid error type "${errorType}" passed to createError.`)
     }
     return error
   }
@@ -703,16 +703,6 @@
       }
     }
 
-    // Executing a command string containing a path to an asar
-    // archive confuses `childProcess.execFile`, which is internally
-    // called by `childProcess.{exec,execSync}`, causing
-    // Electron to consider the full command as a single path
-    // to an archive.
-    const { exec, execSync } = childProcess
-    childProcess.exec = invokeWithNoAsar(exec)
-    childProcess.exec[util.promisify.custom] = invokeWithNoAsar(exec[util.promisify.custom])
-    childProcess.execSync = invokeWithNoAsar(execSync)
-
     function invokeWithNoAsar (func) {
       return function () {
         const processNoAsarOriginalValue = process.noAsar
@@ -732,10 +722,35 @@
     overrideAPISync(fs, 'copyFileSync')
 
     overrideAPI(fs, 'open')
-    overrideAPI(childProcess, 'execFile')
     overrideAPISync(process, 'dlopen', 1)
-    overrideAPISync(require('module')._extensions, '.node', 1)
+    overrideAPISync(Module._extensions, '.node', 1)
     overrideAPISync(fs, 'openSync')
-    overrideAPISync(childProcess, 'execFileSync')
+
+    // Lazily override the child_process APIs only when child_process is fetched the first time
+    const originalModuleLoad = Module._load
+    Module._load = (request, ...args) => {
+      const loadResult = originalModuleLoad(request, ...args)
+      if (request === 'child_process') {
+        if (!v8Util.getHiddenValue(loadResult, 'asar-ready')) {
+          v8Util.setHiddenValue(loadResult, 'asar-ready', true)
+          // Just to make it obvious what we are dealing with here
+          const childProcess = loadResult
+
+          // Executing a command string containing a path to an asar
+          // archive confuses `childProcess.execFile`, which is internally
+          // called by `childProcess.{exec,execSync}`, causing
+          // Electron to consider the full command as a single path
+          // to an archive.
+          const { exec, execSync } = childProcess
+          childProcess.exec = invokeWithNoAsar(exec)
+          childProcess.exec[util.promisify.custom] = invokeWithNoAsar(exec[util.promisify.custom])
+          childProcess.execSync = invokeWithNoAsar(execSync)
+
+          overrideAPI(childProcess, 'execFile')
+          overrideAPISync(childProcess, 'execFileSync')
+        }
+      }
+      return loadResult
+    }
   }
 })()