feat: Adds guard to avoid stepping on Yarn's feet

Author: arcanis

sources/commands/Disable.ts

@@ -70,6 +70,13 @@ export class DisableCommand extends Command<Context> {
   async removePosixLink(installDirectory: string, binName: string) {
     const file = path.join(installDirectory, binName);
     try {
+      const currentTarget = await fs.promises.realpath(file);
+
+      if (binName.includes(`yarn`) && currentTarget.match(/[/\\]switch[/\\]/)) {
+        console.warn(`${binName} is already installed in ${file} and points to a Yarn Switch install - skipping`);
+        return;
+      }
+
       await fs.promises.unlink(file);
     } catch (err) {
       if ((err as NodeError).code !== `ENOENT`) {

sources/commands/Enable.ts

@@ -83,6 +83,13 @@ export class EnableCommand extends Command<Context> {
 
     if (fs.existsSync(file)) {
       const currentSymlink = await fs.promises.readlink(file);
+      const currentTarget = await fs.promises.realpath(file);
+
+      if (binName.includes(`yarn`) && currentTarget.match(/[/\\]switch[/\\]/)) {
+        console.warn(`${binName} is already installed in ${file} and points to a Yarn Switch install - skipping`);
+        return;
+      }
+
       if (currentSymlink !== symlink) {
         await fs.promises.unlink(file);
       } else {

tests/Disable.test.ts

@@ -97,4 +97,23 @@ describe(`DisableCommand`, () => {
       await expect(sortedEntries).resolves.toEqual([...binNames].sort());
     });
   });
+
+  it(`shouldn't remove Yarn binaries if they are in a /switch/ folder`, async () => {
+    await xfs.mktempPromise(async cwd => {
+      await xfs.mkdirPromise(ppath.join(cwd, `switch`));
+      await xfs.writeFilePromise(ppath.join(cwd, `switch/yarn`), `hello`);
+
+      await xfs.linkPromise(
+        ppath.join(cwd, `switch/yarn`),
+        ppath.join(cwd, `yarn`),
+      );
+
+      await expect(runCli(cwd, [`disable`])).resolves.toMatchObject({
+        exitCode: 0,
+      });
+
+      const file = await xfs.readFilePromise(ppath.join(cwd, `yarn`), `utf8`);
+      expect(file).toBe(`hello`);
+    });
+  });
 });

tests/Enable.test.ts

@@ -11,6 +11,10 @@ import {runCli}                                                         from './
 
 const engine = new Engine();
 
+const testNotWindows = process.platform === `win32`
+  ? it.skip
+  : it;
+
 beforeEach(async () => {
   // `process.env` is reset after each tests in setupTests.js.
   process.env.COREPACK_HOME = npath.fromPortablePath(await xfs.mktempPromise());
@@ -87,4 +91,42 @@ describe(`EnableCommand`, () => {
       await expect(sortedEntries).resolves.toEqual(expectedEntries.sort());
     });
   });
+
+  testNotWindows(`should overwrite existing files`, async () => {
+    await xfs.mktempPromise(async cwd => {
+      await xfs.writeFilePromise(ppath.join(cwd, `yarn`), `hello`);
+
+      process.env.PATH = `${npath.fromPortablePath(cwd)}${delimiter}${process.env.PATH}`;
+      await expect(runCli(cwd, [`enable`])).resolves.toMatchObject({
+        stdout: ``,
+        stderr: ``,
+        exitCode: 0,
+      });
+
+      const file = await xfs.readFilePromise(ppath.join(cwd, `yarn`), `utf8`);
+      expect(file).toBe(`hello`);
+    });
+  });
+
+  testNotWindows(`shouldn't overwrite Yarn files if they are in a /switch/ folder`, async () => {
+    await xfs.mktempPromise(async cwd => {
+      await xfs.mkdirPromise(ppath.join(cwd, `switch`));
+      await xfs.writeFilePromise(ppath.join(cwd, `switch/yarn`), `hello`);
+
+      await xfs.linkPromise(
+        ppath.join(cwd, `switch/yarn`),
+        ppath.join(cwd, `yarn`),
+      );
+
+      process.env.PATH = `${npath.fromPortablePath(cwd)}${delimiter}${process.env.PATH}`;
+      await expect(runCli(cwd, [`enable`])).resolves.toMatchObject({
+        stdout: ``,
+        stderr: ``,
+        exitCode: 0,
+      });
+
+      const file = await xfs.readFilePromise(ppath.join(cwd, `yarn`), `utf8`);
+      expect(file).toBe(`hello`);
+    });
+  });
 });