From 836f8fda216ea23c5361a5785bf5d79a4fba5036 Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@gmail.com>
Date: Wed, 25 Oct 2017 16:38:19 +0100
Subject: [PATCH 1/4] Preserve module identity for symlinks

---
 integration_tests/__tests__/resolve.test.js         | 6 +++++-
 integration_tests/resolve/__tests__/resolve.test.js | 6 ++++++
 packages/jest-resolve/src/default_resolver.js       | 6 +++++-
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/integration_tests/__tests__/resolve.test.js b/integration_tests/__tests__/resolve.test.js
index 24bc9a436ae6..f9b50c4c4508 100644
--- a/integration_tests/__tests__/resolve.test.js
+++ b/integration_tests/__tests__/resolve.test.js
@@ -12,5 +12,9 @@ const runJest = require('../runJest');
 
 test('resolve platform modules', () => {
   const result = runJest('resolve');
-  expect(result.status).toBe(0);
+  const didFail = result.status !== 0;
+  if (didFail) {
+    console.log(result.stderr);
+  }
+  expect(didFail).toBe(false);
 });
diff --git a/integration_tests/resolve/__tests__/resolve.test.js b/integration_tests/resolve/__tests__/resolve.test.js
index 7e66c5d06c8e..41a840c2d56d 100644
--- a/integration_tests/resolve/__tests__/resolve.test.js
+++ b/integration_tests/resolve/__tests__/resolve.test.js
@@ -56,3 +56,9 @@ test('should resolve filename.json', () => {
   expect(testRequire('../test4')).not.toThrow();
   expect(platform.extension).toBe('json');
 });
+
+test('should preserve identity for symlinks', () => {
+  expect(require('../../../packages/jest-resolve')).toBe(
+    require('jest-resolve')
+  );
+});
diff --git a/packages/jest-resolve/src/default_resolver.js b/packages/jest-resolve/src/default_resolver.js
index 56c4fc539a38..30a5c5151d4c 100644
--- a/packages/jest-resolve/src/default_resolver.js
+++ b/packages/jest-resolve/src/default_resolver.js
@@ -25,7 +25,6 @@ export default function defaultResolver(
   options: ResolverOptions,
 ): Path {
   const resolve = options.browser ? browserResolve.sync : resolveSync;
-
   return resolve(path, {
     basedir: options.basedir,
     extensions: options.extensions,
@@ -94,6 +93,11 @@ function resolveSync(target: Path, options: ResolverOptions): Path {
     if (isDirectory(dir)) {
       result = resolveAsFile(name) || resolveAsDirectory(name);
     }
+    if (result) {
+      // Dereference symlinks to ensure we don't create a separate
+      // module instance depending on how it was referenced.
+      result = fs.realpathSync(result);
+    }
     return result;
   }
 

From a1c65e981c63959c379425f518e2f52e4d861308 Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@gmail.com>
Date: Wed, 25 Oct 2017 16:52:47 +0100
Subject: [PATCH 2/4] Add changelog entry

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e07e38a4ac6a..33808e0697bd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@
 * `[jest-message-util]` Always remove node internals from stacktraces ([#4695](https://github.com/facebook/jest/pull/4695))
 * `[jest-resolve]` changes method of determining builtin modules to include missing builtins ([#4740](https://github.com/facebook/jest/pull/4740))
 * `[pretty-format]` Prevent error in pretty-format for window in jsdom test env ([#4750](https://github.com/facebook/jest/pull/4750))
+* `[jest-resolve]` Preserve module identity for symlinks ([#4761](https://github.com/facebook/jest/pull/4761))
 
 ### Features
 * `[jest-environment-*]` [**BREAKING**] Add Async Test Environment APIs, dispose is now teardown ([#4506](https://github.com/facebook/jest/pull/4506))

From 8f651e7dbf79b65f5ca4027f135946a039ee9e45 Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@gmail.com>
Date: Wed, 25 Oct 2017 16:57:24 +0100
Subject: [PATCH 3/4] Remove unintentional whitespace change

---
 packages/jest-resolve/src/default_resolver.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/packages/jest-resolve/src/default_resolver.js b/packages/jest-resolve/src/default_resolver.js
index 30a5c5151d4c..324777bec194 100644
--- a/packages/jest-resolve/src/default_resolver.js
+++ b/packages/jest-resolve/src/default_resolver.js
@@ -25,6 +25,7 @@ export default function defaultResolver(
   options: ResolverOptions,
 ): Path {
   const resolve = options.browser ? browserResolve.sync : resolveSync;
+
   return resolve(path, {
     basedir: options.basedir,
     extensions: options.extensions,

From 50f000e241cdff7e80a3d5eed231841231ce0038 Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@gmail.com>
Date: Wed, 25 Oct 2017 18:55:40 +0100
Subject: [PATCH 4/4] Revert integration test to undebuggable state

---
 integration_tests/__tests__/resolve.test.js | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/integration_tests/__tests__/resolve.test.js b/integration_tests/__tests__/resolve.test.js
index f9b50c4c4508..24bc9a436ae6 100644
--- a/integration_tests/__tests__/resolve.test.js
+++ b/integration_tests/__tests__/resolve.test.js
@@ -12,9 +12,5 @@ const runJest = require('../runJest');
 
 test('resolve platform modules', () => {
   const result = runJest('resolve');
-  const didFail = result.status !== 0;
-  if (didFail) {
-    console.log(result.stderr);
-  }
-  expect(didFail).toBe(false);
+  expect(result.status).toBe(0);
 });