fix(@schematics/angular): ignore non-workspace stylesheet entries when adding Tailwind

packages/schematics/angular/tailwind/index.ts

@@ -48,9 +48,11 @@ function addTailwindStyles(options: { project: string }, project: ProjectDefinit
 
     let stylesheetPath: string | undefined;
     if (styles) {
+      // Only consider workspace source files. Entries such as package specifiers
+      // (`@angular/material/prebuilt-themes/...`) or files within `node_modules` must not be modified.
       stylesheetPath = styles
         .map((s) => (typeof s === 'string' ? s : s.input))
-        .find((p) => p.endsWith('.css'));
+        .find((p) => p.endsWith('.css') && !/(?:^|\/)node_modules\//.test(p) && tree.exists(p));
     }
 
     if (!stylesheetPath) {

packages/schematics/angular/tailwind/index_spec.ts

@@ -129,4 +129,40 @@ describe('Tailwind Schematic', () => {
       expect(tree.exists('/projects/bar/.postcssrc.json')).toBe(false);
     });
   });
+
+  describe('with non-workspace stylesheets', () => {
+    function setStyles(tree: UnitTestTree, styles: string[]): void {
+      const workspace = getWorkspace(tree);
+      workspace.projects.bar.architect.build.options.styles = styles;
+      tree.overwrite('/angular.json', JSON.stringify(workspace, null, 2));
+    }
+
+    it('should create a tailwind stylesheet when the only CSS entry is a package theme', async () => {
+      setStyles(appTree, [
+        '@angular/material/prebuilt-themes/azure-blue.css',
+        'projects/bar/src/styles.scss',
+      ]);
+
+      const tree = await schematicRunner.runSchematic('tailwind', { project: 'bar' }, appTree);
+
+      expect(tree.exists('/projects/bar/src/tailwind.css')).toBe(true);
+      const workspace = getWorkspace(tree);
+      expect(workspace.projects.bar.architect.build.options.styles).toEqual([
+        'projects/bar/src/tailwind.css',
+        '@angular/material/prebuilt-themes/azure-blue.css',
+        'projects/bar/src/styles.scss',
+      ]);
+    });
+
+    it('should not modify a stylesheet inside node_modules', async () => {
+      const vendorStylesheet = 'node_modules/bootstrap/dist/css/bootstrap.min.css';
+      appTree.create(`/${vendorStylesheet}`, 'body { margin: 0; }');
+      setStyles(appTree, [vendorStylesheet, 'projects/bar/src/styles.css']);
+
+      const tree = await schematicRunner.runSchematic('tailwind', { project: 'bar' }, appTree);
+
+      expect(tree.readContent(`/${vendorStylesheet}`)).not.toContain('tailwindcss');
+      expect(tree.readContent('/projects/bar/src/styles.css')).toContain(`@import 'tailwindcss';`);
+    });
+  });
 });