fix(compiler): log warning for missing name/namespace (#4825)

packages/@lwc/babel-plugin-component/src/__tests__/warnings.spec.ts

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2024, salesforce.com, inc.
+ * All rights reserved.
+ * SPDX-License-Identifier: MIT
+ * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
+ */
+import { afterEach, beforeEach, expect, vi, test } from 'vitest';
+import { transformSync } from '@babel/core';
+import plugin from '../index';
+
+let spy;
+
+beforeEach(() => {
+    spy = vi.spyOn(console, 'warn');
+});
+
+afterEach(() => {
+    spy!.mockReset();
+});
+
+test('warns on missing name/namespace', () => {
+    const source = `
+        import { LightningElement } from 'lwc';
+        export default class extends LightningElement {};
+    `;
+
+    const { code } = transformSync(source, {
+        babelrc: false,
+        configFile: false,
+        filename: `foo.js`,
+        plugins: [
+            [
+                plugin,
+                {
+                    namespace: '',
+                    name: '',
+                },
+            ],
+        ],
+    })!;
+
+    // compilation works successfully
+    expect(code).toBeTypeOf('string');
+
+    expect(spy!).toHaveBeenCalledOnce();
+    expect(spy!).toHaveBeenCalledWith(
+        'The namespace and name should both be non-empty strings. You may get unexpected behavior at runtime. Found: namespace="" and name=""'
+    );
+});

packages/@lwc/babel-plugin-component/src/types.ts

@@ -17,8 +17,8 @@ export interface LwcBabelPluginOptions {
         loader?: string;
         strictSpecifier?: boolean;
     };
-    namespace?: string;
-    name?: string;
+    namespace: string;
+    name: string;
     instrumentation?: InstrumentationObject;
     apiVersion?: number;
 }

packages/@lwc/compiler/src/options.ts

@@ -95,9 +95,9 @@ export interface DynamicImportConfig {
  */
 export interface TransformOptions {
     /** The name of the component. For example, the name in `<my-component>` is `"component"`. */
-    name?: string;
+    name: string;
     /** The namespace of the component. For example, the namespace in `<my-component>` is `"my"`. */
-    namespace?: string;
+    namespace: string;
     /** @deprecated Ignored by compiler. */
     stylesheetConfig?: StylesheetConfig;
     // TODO [#5031]: Unify dynamicImports and experimentalDynamicComponent options

packages/@lwc/rollup-plugin/src/index.ts

@@ -334,6 +334,17 @@ export default function lwc(pluginOptions: RollupLwcOptions = {}): Plugin {
                 // a '/' regardless of Windows vs Unix, since it comes from the Rollup `id`
                 specifier?.split('/') ?? path.dirname(filename).split('/').slice(-2);
 
+            /* v8 ignore next */
+            if (!namespace || !name) {
+                // TODO [#4824]: Make this an error rather than a warning
+                this.warn(
+                    'The component namespace and name could not be determined from the specifier ' +
+                        JSON.stringify(specifier) +
+                        ' or filename ' +
+                        JSON.stringify(filename)
+                );
+            }
+
             const apiVersionToUse = getAPIVersionFromNumber(apiVersion);
 
             const { code, map, warnings } = transformSync(src, filename, {

packages/@lwc/shared/src/custom-element.ts

@@ -15,6 +15,18 @@
  * @returns component tag name
  */
 export function generateCustomElementTagName(namespace: string = '', name: string = '') {
+    if (!namespace || !name) {
+        // TODO [#4824]: Make this an error rather than a warning
+        // eslint-disable-next-line no-console
+        console.warn(
+            'The namespace and name should both be non-empty strings. ' +
+                'You may get unexpected behavior at runtime. ' +
+                'Found: namespace=' +
+                JSON.stringify(namespace) +
+                ' and name=' +
+                JSON.stringify(namespace)
+        );
+    }
     const kebabCasedName = name.replace(/([a-z])([A-Z])/g, '$1-$2').toLowerCase();
     return `${namespace}-${kebabCasedName}`;
 }