From af933a2f9e616b3e84d6c95cb3c42616a463f3af Mon Sep 17 00:00:00 2001
From: Brian Donovan <1938+eventualbuddha@users.noreply.github.com>
Date: Tue, 29 Jan 2019 16:40:20 -0800
Subject: [PATCH] fix: snapshot `global` when loading plugins

This allows us to load anything that modifies the `global` object and then restore it afterward. This is needed in particular for `@babel/polyfill` since it sets a global property to try to warn the user if it's being loaded more than once.
---
 packages/cli/src/ProcessSnapshot.ts           | 10 +++
 packages/cli/test/unit/ProcessSnapshotTest.ts | 83 +++++++++++++++++--
 2 files changed, 84 insertions(+), 9 deletions(-)

diff --git a/packages/cli/src/ProcessSnapshot.ts b/packages/cli/src/ProcessSnapshot.ts
index faa2aa80..8db7b9fc 100644
--- a/packages/cli/src/ProcessSnapshot.ts
+++ b/packages/cli/src/ProcessSnapshot.ts
@@ -32,11 +32,13 @@ export default class ProcessSnapshot {
   constructor(
     private readonly requireImpl: typeof require = require,
     private readonly processImpl: typeof process = process,
+    private readonly originalGlobal: typeof global = global,
     private readonly log: typeof console.log = () => {}
   ) {
     this.cacheEntries = this.snapshotRequireCache();
     this.extensions = this.snapshotRequireExtensions();
     this.processEvents = this.snapshotProcessEvents();
+    this.originalGlobal.global = Object.create(originalGlobal);
   }
 
   /**
@@ -46,6 +48,7 @@ export default class ProcessSnapshot {
     this.restoreRequireCache();
     this.restoreExtensions();
     this.restoreProcessEvents();
+    this.restoreGlobal();
   }
 
   /**
@@ -172,6 +175,13 @@ export default class ProcessSnapshot {
     }
   }
 
+  /**
+   * Restores the state of the `global` object.
+   */
+  private restoreGlobal(): void {
+    this.originalGlobal.global = this.originalGlobal;
+  }
+
   /**
    * Snapshots the current state of `require.cache`.
    */
diff --git a/packages/cli/test/unit/ProcessSnapshotTest.ts b/packages/cli/test/unit/ProcessSnapshotTest.ts
index 9f05202f..d3f2f8bc 100644
--- a/packages/cli/test/unit/ProcessSnapshotTest.ts
+++ b/packages/cli/test/unit/ProcessSnapshotTest.ts
@@ -5,6 +5,7 @@ import ProcessSnapshot from '../../src/ProcessSnapshot';
 describe('ProcessSnapshot', function() {
   let fakeRequire: typeof require;
   let fakeProcess: typeof process;
+  let fakeGlobal: typeof global;
   let messages: Array<string>;
 
   function log(...args: Array<{}>): void {
@@ -21,12 +22,19 @@ describe('ProcessSnapshot', function() {
     fakeProcess['_events'] = Object.create(fakeProcess['_events']);
     fakeProcess.removeAllListeners();
 
+    fakeGlobal = Object.create(global);
+
     messages = [];
   });
 
   it('removes added require entries from the cache', function() {
     // Take a snapshot.
-    let snapshot = new ProcessSnapshot(fakeRequire, fakeProcess, log);
+    let snapshot = new ProcessSnapshot(
+      fakeRequire,
+      fakeProcess,
+      fakeGlobal,
+      log
+    );
 
     // Add a file to the cache.
     let path = '/some/added/file';
@@ -47,7 +55,12 @@ describe('ProcessSnapshot', function() {
     ok(path in fakeRequire.cache);
 
     // Take a snapshot.
-    let snapshot = new ProcessSnapshot(fakeRequire, fakeProcess, log);
+    let snapshot = new ProcessSnapshot(
+      fakeRequire,
+      fakeProcess,
+      fakeGlobal,
+      log
+    );
 
     // Remove a file from the cache.
     delete fakeRequire.cache[path];
@@ -70,7 +83,12 @@ describe('ProcessSnapshot', function() {
     ok(path in fakeRequire.cache);
 
     // Take a snapshot.
-    let snapshot = new ProcessSnapshot(fakeRequire, fakeProcess, log);
+    let snapshot = new ProcessSnapshot(
+      fakeRequire,
+      fakeProcess,
+      fakeGlobal,
+      log
+    );
 
     // Replace a file in the cache.
     fakeRequire.cache[path] = new Module(path);
@@ -86,7 +104,12 @@ describe('ProcessSnapshot', function() {
 
   it('removes added require extensions', function() {
     // Take a snapshot.
-    let snapshot = new ProcessSnapshot(fakeRequire, fakeProcess, log);
+    let snapshot = new ProcessSnapshot(
+      fakeRequire,
+      fakeProcess,
+      fakeGlobal,
+      log
+    );
 
     // Add a require extension.
     fakeRequire.extensions['.omg'] = () => {};
@@ -103,7 +126,12 @@ describe('ProcessSnapshot', function() {
     fakeRequire.extensions['.omg'] = () => {};
 
     // Take a snapshot.
-    let snapshot = new ProcessSnapshot(fakeRequire, fakeProcess, log);
+    let snapshot = new ProcessSnapshot(
+      fakeRequire,
+      fakeProcess,
+      fakeGlobal,
+      log
+    );
 
     // Remove the extension.
     delete fakeRequire.extensions['.omg'];
@@ -121,7 +149,12 @@ describe('ProcessSnapshot', function() {
     fakeRequire.extensions['.omg'] = originalLoader;
 
     // Take a snapshot.
-    let snapshot = new ProcessSnapshot(fakeRequire, fakeProcess, log);
+    let snapshot = new ProcessSnapshot(
+      fakeRequire,
+      fakeProcess,
+      fakeGlobal,
+      log
+    );
 
     // Replace a require extension.
     fakeRequire.extensions['.omg'] = () => {};
@@ -135,7 +168,12 @@ describe('ProcessSnapshot', function() {
 
   it('removes added process event listeners', function() {
     // Take a snapshot.
-    let snapshot = new ProcessSnapshot(fakeRequire, fakeProcess, log);
+    let snapshot = new ProcessSnapshot(
+      fakeRequire,
+      fakeProcess,
+      fakeGlobal,
+      log
+    );
 
     // Add an event listener.
     let listener = (): void => {};
@@ -154,7 +192,12 @@ describe('ProcessSnapshot', function() {
     fakeProcess.on('exit', listener);
 
     // Take a snapshot.
-    let snapshot = new ProcessSnapshot(fakeRequire, fakeProcess, log);
+    let snapshot = new ProcessSnapshot(
+      fakeRequire,
+      fakeProcess,
+      fakeGlobal,
+      log
+    );
 
     // Remove the event listener.
     fakeProcess.removeListener('exit', listener);
@@ -172,7 +215,12 @@ describe('ProcessSnapshot', function() {
     fakeProcess.on('exit', existingListener);
 
     // Take a snapshot.
-    let snapshot = new ProcessSnapshot(fakeRequire, fakeProcess, log);
+    let snapshot = new ProcessSnapshot(
+      fakeRequire,
+      fakeProcess,
+      fakeGlobal,
+      log
+    );
 
     // Add an event listener.
     let listener = (): void => {};
@@ -184,4 +232,21 @@ describe('ProcessSnapshot', function() {
     deepEqual(messages, [`removing added 'exit' event listener`]);
     deepEqual(fakeProcess.listeners('exit'), [existingListener]);
   });
+
+  it('restores `global`', function() {
+    // Take a snapshot.
+    let snapshot = new ProcessSnapshot(
+      fakeRequire,
+      fakeProcess,
+      fakeGlobal,
+      log
+    );
+
+    fakeGlobal.global['foo'] = 123;
+
+    // Restore the snapshot.
+    snapshot.restore();
+
+    strictEqual(fakeGlobal.global['foo'], undefined);
+  });
 });