allow upgrades in pnpm workspace root

When using pnpm with a workspace, if you happen to run the upgrade tool
in the root because some Tailwind CSS dependencies live there, then you
will get an error that you need the `--workspace-root` flag.

However, if we _always_ add it, then the upgrade tool will add
dependencies to the root, regardless of whether you are in a
sub-packages.

With this, the check doesn't happen and no error is thrown. This will
just install/bump the dependencies where necessary.

Author: RobinMalfait

integrations/upgrade/index.test.ts

@@ -3091,7 +3091,29 @@ test(
       'Running this command will add the dependency to the workspace root',
     )
 
-    expect(await fs.dumpFiles('./src/**/*.{css,html}')).toMatchInlineSnapshot()
+    expect(await fs.dumpFiles('./src/**/*.{css,html}')).toMatchInlineSnapshot(`
+      "
+      --- ./src/index.html ---
+      <!-- Migrating 'ring', 'rounded' and 'outline-none' are unsafe in v4 -> v4 migrations -->
+      <div class="ring rounded outline"></div>
+
+      <!-- Variant order is also unsafe to change in v4 projects -->
+      <div class="file:hover:flex *:hover:flex"></div>
+      <div class="hover:file:flex hover:*:flex"></div>
+
+      <!-- These are safe to migrate: -->
+      <div
+        class="flex! bg-red-500/(--my-opacity) pointer-fine:flex bg-bottom-right object-top-left"
+      ></div>
+
+      --- ./src/input.css ---
+      @import 'tailwindcss';
+
+      .foo {
+        @apply bg-(--my-color)!;
+      }
+      "
+    `)
   },
 )
 

packages/@tailwindcss-upgrade/src/utils/packages.ts

@@ -31,6 +31,13 @@ export function pkg(base: string) {
         args.push(SAVE_DEV[packageManager] || SAVE_DEV.default)
       }
 
+      // Allow running the `pnpm` command in the workspace root without
+      // erroring. Can't just use `--workspace-root` because that will force
+      // install dependencies in the workspace root.
+      if (packageManager === 'pnpm') {
+        args.push('--ignore-workspace-root-check')
+      }
+
       let command = `${packageManager} add ${args.join(' ')}`
       try {
         return await exec(command, { cwd: base })