Prevents cache removal when running an install

CHANGELOG.md

@@ -4,19 +4,22 @@ Please add one entry in this file for each change in Yarn's behavior. Use the sa
 
 ## Master
 
+- Folders like `.cache` won't be pruned from the `node_modules` after each install.
+
+  [#7699](https://github.com/yarnpkg/yarn/pull/7699) - [**Maël Nison**](https://twitter.com/arcanis)
+
 - Correctly installs workspace child dependencies when workspace child not symlinked to root.
 
   [#7289](https://github.com/yarnpkg/yarn/pull/7289) - [**Daniel Tschinder**](https://github.com/danez)
 
-- Makes running scripts with Plug'n Play possible on node 13
+- Makes running scripts with Plug'n Play possible on node 13.
 
   [#7650](https://github.com/yarnpkg/yarn/pull/7650) - [**Sander Verweij**](https://github.com/sverweij)
 
 - Change run command to check cwd/node_modules/.bin for commands. Fixes run in workspaces.
 
   [#7151](https://github.com/yarnpkg/yarn/pull/7151) - [**Jeff Valore**](https://twitter.com/codingwithspike)
 
-
 ## 1.19.1
 
 **Important:** This release contains a cache bump. It will cause the very first install following the upgrade to take slightly more time, especially if you don't use the [Offline Mirror](https://yarnpkg.com/blog/2016/11/24/offline-mirror/) feature. After that everything will be back to normal.

__tests__/commands/install/integration.js

@@ -117,6 +117,16 @@ test('installing a package with a renamed file should not delete it', () =>
     expect(await fs.exists(`${config.cwd}/node_modules/pkg/state.js`)).toEqual(true);
   }));
 
+test("installing a tree shouldn't remove preexisting cache directories", () =>
+  runInstall({}, 'cache-folder-nm', async (config, reporter): Promise<void> => {
+    expect(await fs.exists(`${config.cwd}/node_modules/.cache/hello.txt`)).toEqual(true);
+
+    const reInstall = new Install({}, config, reporter, await Lockfile.fromDirectory(config.cwd));
+    await reInstall.init();
+
+    expect(await fs.exists(`${config.cwd}/node_modules/.cache/hello.txt`)).toEqual(true);
+  }));
+
 test("installing a new package should correctly update it, even if the files mtime didn't change", () =>
   runInstall({}, 'mtime-same', async (config, reporter): Promise<void> => {
     await misc.sleep(2000);

__tests__/fixtures/install/cache-folder-nm/package.json

@@ -0,0 +1,5 @@
+{
+    "dependencies": {
+        "feed": "0.3.0"
+    }
+}

__tests__/fixtures/install/cache-folder-nm/yarn.lock

@@ -0,0 +1,13 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+feed@0.3.0:
+  version "0.3.0"
+  resolved "https://registry.yarnpkg.com/feed/-/feed-0.3.0.tgz#65bcc4c9c57fde8e277faf4afff80c2d1d90e82d"
+  dependencies:
+    xml ">= 0.0.5"
+
+"xml@>= 0.0.5":
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/xml/-/xml-1.0.1.tgz#78ba72020029c5bc87b8a81a3cfcd74b4a2fc1e5"

src/package-linker.js

@@ -346,6 +346,10 @@ export default class PackageLinker {
               for (const subfile of await fs.readdir(filepath)) {
                 possibleExtraneous.add(path.join(filepath, subfile));
               }
+            } else if (file[0] === '.' && file !== '.bin') {
+              if (!(await fs.lstat(filepath)).isDirectory()) {
+                possibleExtraneous.add(filepath);
+              }
             } else {
               possibleExtraneous.add(filepath);
             }