From 2223dc06fd4f5a1988ee18844f877f38b18ce15d Mon Sep 17 00:00:00 2001
From: David Gobaud <240811+dgobaud@users.noreply.github.com>
Date: Wed, 7 Aug 2019 19:05:22 -0700
Subject: [PATCH 1/2] fix crash when using from cli

require.main is undefined when running from cli - don't use unless it exists
---
 index.js | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/index.js b/index.js
index 7551a0f..2ea21a3 100644
--- a/index.js
+++ b/index.js
@@ -82,7 +82,9 @@ function addPath (path) {
   if (modulePaths.indexOf(path) === -1) {
     modulePaths.push(path)
     // Enable the search path for the current top-level module
-    addPathHelper(path, require.main.paths)
+    if (require.main) {
+      addPathHelper(path, require.main.paths)
+    }
     parent = module.parent
 
     // Also modify the paths of the module that was used to load the
@@ -115,7 +117,9 @@ function addAlias (alias, target) {
 function reset () {
   // Reset all changes in paths caused by addPath function
   modulePaths.forEach(function (path) {
-    removePathHelper(path, require.main.paths)
+    if (require.main) {
+      removePathHelper(path, require.main.paths)
+    }
 
     // Delete from require.cache if the module has been required before.
     // This is required for node >= 11

From b37745065d36dbd013334be0656de5dc35d6e25d Mon Sep 17 00:00:00 2001
From: Daniel Garnier-Moiroux <git@garnier.wf>
Date: Mon, 30 Sep 2019 08:50:25 +0200
Subject: [PATCH 2/2] Add tests for REPL mode

- This require introducing a way of having "require.main" undefined
  in our module. The require function is different between the test
  module and the module under test, so we can't just do
  `require.main = null`
  in the test function, as it won't affect the "require" function
  of the prod code. So we need to introduce a helper function for
  evaluating require.main, and injact a flag in the test module
  when running the tests.
---
 index.js      | 19 +++++++++++++------
 test/specs.js | 18 ++++++++++++++++++
 2 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/index.js b/index.js
index 2ea21a3..8f2e570 100644
--- a/index.js
+++ b/index.js
@@ -82,14 +82,15 @@ function addPath (path) {
   if (modulePaths.indexOf(path) === -1) {
     modulePaths.push(path)
     // Enable the search path for the current top-level module
-    if (require.main) {
-      addPathHelper(path, require.main.paths)
+    var mainModule = getMainModule()
+    if (mainModule) {
+      addPathHelper(path, mainModule.paths)
     }
     parent = module.parent
 
     // Also modify the paths of the module that was used to load the
     // app-module-paths module and all of it's parents
-    while (parent && parent !== require.main) {
+    while (parent && parent !== mainModule) {
       addPathHelper(path, parent.paths)
       parent = parent.parent
     }
@@ -115,10 +116,12 @@ function addAlias (alias, target) {
  * The function is undocumented and for testing purposes only
  */
 function reset () {
+  var mainModule = getMainModule()
+
   // Reset all changes in paths caused by addPath function
   modulePaths.forEach(function (path) {
-    if (require.main) {
-      removePathHelper(path, require.main.paths)
+    if (mainModule) {
+      removePathHelper(path, mainModule.paths)
     }
 
     // Delete from require.cache if the module has been required before.
@@ -130,7 +133,7 @@ function reset () {
     })
 
     var parent = module.parent
-    while (parent && parent !== require.main) {
+    while (parent && parent !== mainModule) {
       removePathHelper(path, parent.paths)
       parent = parent.parent
     }
@@ -209,6 +212,10 @@ function init (options) {
   }
 }
 
+function getMainModule () {
+  return require.main._simulateRepl ? undefined : require.main
+}
+
 module.exports = init
 module.exports.addPath = addPath
 module.exports.addAlias = addAlias
diff --git a/test/specs.js b/test/specs.js
index 0582e79..4793827 100644
--- a/test/specs.js
+++ b/test/specs.js
@@ -158,6 +158,24 @@ describe('module-alias', function () {
     })
   })
 
+  context('when used from the REPL', function () {
+    before(function () {
+      require.main._simulateRepl = true
+    })
+
+    after(function () {
+      delete require.main._simulateRepl
+    })
+
+    it('should addPath', function () {
+      moduleAlias.addPath('some-path')
+    })
+
+    it('should reset', function () {
+      moduleAlias.reset()
+    })
+  })
+
   it('should support forked modules', function () {
     expect(typeof require('hello-world-classic')).to.equal('function')
   })