fix(cli): report error when plugin module cannot be resolved

Previously, when a plugin module couldn't be found (e.g., package not
installed), the error was silently swallowed and the plugin was skipped.
Now the CLI reports a clear error message distinguishing between missing
modules and other loading failures.

Closes #2393

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ymc9

packages/cli/src/actions/generate.ts

@@ -340,10 +340,15 @@ async function loadPluginModule(provider: string, basePath: string) {
 
     // last resort, try to import as esm directly
     try {
-        return (await import(moduleSpec)).default as CliPlugin;
-    } catch {
-        // plugin may not export a generator so we simply ignore the error here
-        return undefined;
+        const mod = await import(moduleSpec);
+        // plugin may not export a generator, return undefined in that case
+        return mod.default as CliPlugin | undefined;
+    } catch (err) {
+        const errorCode = (err as NodeJS.ErrnoException)?.code;
+        if (errorCode === 'ERR_MODULE_NOT_FOUND' || errorCode === 'MODULE_NOT_FOUND') {
+            throw new CliError(`Cannot find plugin module "${provider}". Please make sure the package exists.`);
+        }
+        throw new CliError(`Failed to load plugin module "${provider}": ${(err as Error).message}`);
     }
 }
 

packages/cli/test/generate.test.ts

@@ -199,6 +199,60 @@ model User {
         expect(fs.existsSync(path.join(workDir, 'zenstack/input.ts'))).toBe(false);
     });
 
+    it('should report error for unresolvable plugin module', async () => {
+        const modelWithMissingPlugin = `
+plugin foo {
+    provider = '@zenstackhq/nonexistent-plugin'
+}
+
+model User {
+    id String @id @default(cuid())
+}
+`;
+        const { workDir } = await createProject(modelWithMissingPlugin);
+        expect(() => runCli('generate', workDir)).toThrow(/Cannot find plugin module/);
+    });
+
+    it('should succeed when plugin module exists but has no CLI generator', async () => {
+        const modelWithNoGeneratorPlugin = `
+plugin foo {
+    provider = './my-plugin.mjs'
+}
+
+model User {
+    id String @id @default(cuid())
+}
+`;
+        const { workDir } = await createProject(modelWithNoGeneratorPlugin);
+        // Create a plugin module that doesn't export a default CLI generator
+        fs.writeFileSync(path.join(workDir, 'zenstack/my-plugin.mjs'), 'export const name = "no-generator";');
+        runCli('generate', workDir);
+        // Should succeed without error, generating the default typescript output
+        expect(fs.existsSync(path.join(workDir, 'zenstack/schema.ts'))).toBe(true);
+    });
+
+    it('should succeed when plugin only provides a plugin.zmodel for custom attributes', async () => {
+        const modelWithZmodelOnlyPlugin = `
+plugin myPlugin {
+    provider = './my-plugin'
+}
+
+model User {
+    id String @id @default(cuid())
+    @@custom
+}
+`;
+        const { workDir } = await createProject(modelWithZmodelOnlyPlugin);
+        // Create a plugin directory with index.mjs (no default export) and a plugin.zmodel defining a custom attribute
+        const pluginDir = path.join(workDir, 'zenstack/my-plugin');
+        fs.mkdirSync(pluginDir, { recursive: true });
+        fs.writeFileSync(path.join(pluginDir, 'index.mjs'), 'export const name = "my-plugin";');
+        fs.writeFileSync(path.join(pluginDir, 'plugin.zmodel'), 'attribute @@custom()');
+        runCli('generate', workDir);
+        // Should succeed without error, generating the default typescript output
+        expect(fs.existsSync(path.join(workDir, 'zenstack/schema.ts'))).toBe(true);
+    });
+
     it('should prefer CLI options over @core/typescript plugin settings for generateModels and generateInput', async () => {
         const modelWithPlugin = `
 plugin typescript {