use loader mechanism to detect presence of loader

CHANGELOG.md

@@ -1,5 +1,8 @@
 # changelog
 
+ * 2.0.7 _Oct.??.2022_
+   * [use loader mechanism to detect](https://github.com/iambumblehead/esmock/pull/180) presence of esmock loader
+   * [detect and use import.meta.resolve,](https://github.com/iambumblehead/esmock/pull/179) when defined by host environment
  * 2.0.6 _Oct.14.2022_
    * [show full path at error message,](https://github.com/iambumblehead/esmock/pull/170) making it easier to identify an invalid path
  * 2.0.5 _Oct.05.2022_

src/esmock.js

@@ -1,12 +1,13 @@
 import esmockIsLoader from './esmockIsLoader.js'
 import esmockModule from './esmockModule.js'
 import esmockArgs from './esmockArgs.js'
+import esmockErr from './esmockErr.js'
 
 const esmockGo = opts => async (...args) => {
-  if (!esmockIsLoader())
-    throw new Error('process must be started with --loader=esmock')
-
   const [moduleId, parent, defs, gdefs, opt] = esmockArgs(args, opts)
+  if (!(await esmockIsLoader()))
+    throw esmockErr.errMissingLoader()
+
   const fileURLKey = await esmockModule(moduleId, parent, defs, gdefs, opt)
   const importedModule = await import(fileURLKey)
 

src/esmockErr.js

@@ -4,7 +4,12 @@ const errModuleIdNotFound = (moduleId, parent) =>
 const errModuleIdNotMocked = (moduleId, parent) =>
   new Error(`un-mocked moduleId: "${moduleId}" (used by ${parent})`)
 
+const errMissingLoader = () =>
+  new Error('the loader chain process must include esmock. '
+    + 'start the process using --loader=esmock.')
+
 export default {
   errModuleIdNotFound,
-  errModuleIdNotMocked
+  errModuleIdNotMocked,
+  errMissingLoader
 }

src/esmockIsLoader.js

@@ -1,5 +1,4 @@
-const isloaderRe = /--(experimental-)?loader[=\s,"']*esmock/
+import { loaderIsVerified } from './esmockLoader.js'
 
-export default (pr = process) =>
-  isloaderRe.test(pr.execArgv) ||
-  isloaderRe.test(pr.env.NODE_OPTIONS)
+export default (c => async () =>
+  c || (c = await loaderIsVerified(import.meta.url)))()

src/esmockLoader.js

@@ -80,7 +80,20 @@ const resolve = async (specifier, context, nextResolve) => {
   return resolved
 }
 
+const loaderVerificationQuery = 'esmock-loader=true'
+const loaderVerificationURLCreate = url => `${url}?${loaderVerificationQuery}`
+const loaderIsVerified = async url =>
+  (await import(loaderVerificationURLCreate(url))).default === true
 const load = async (url, context, nextLoad) => {
+  if (url.endsWith(loaderVerificationQuery)) {
+    return {
+      format: 'module',
+      shortCircuit: true,
+      responseURL: url,
+      source: 'export default true'
+    }
+  }
+
   if (esmkdefsRe.test(url)) // parent of mocked modules
     return nextLoad(url, context)
 
@@ -113,4 +126,4 @@ const getSource = isLT1612 && load
 
 export * from './esmock.js'
 export {default} from './esmock.js'
-export {load, resolve, getSource}
+export {load, resolve, getSource, loaderIsVerified}

tests/tests-no-loader/esmock.noloader.test.js

@@ -1,9 +1,10 @@
 import test from 'node:test'
 import assert from 'node:assert/strict'
 import esmock from 'esmock'
+import esmockErr from '../../src/esmockErr.js'
 
 test('should throw error if !esmockloader', async () => {
   await assert.rejects(() => esmock('./to/module.js'), {
-    message: 'process must be started with --loader=esmock'
+    message: esmockErr.errMissingLoader().message
   })
 })