fix: warn when .d.ts files are required, fixes #372, #320

src/__test__/import-empty-declaration.ts

@@ -0,0 +1,19 @@
+import {
+    src, webpackConfig, tsconfig,
+    compile, expectErrors, expectWarnings, spec
+} from './utils';
+
+spec(__filename, async function() {
+    src('index.ts', `
+        import './empty.d.ts'
+    `);
+
+    src('empty.d.ts', ``);
+    tsconfig();
+
+    const stats = await compile(webpackConfig());
+    expectErrors(stats, 0);
+    expectWarnings(stats, 1, [
+        'TypeScript declaration files should never be required'
+    ]);
+});

src/__test__/utils.ts

@@ -236,6 +236,15 @@ export function expectErrors(stats: any, count: number, errors: string[] = []) {
     expect(stats.compilation.errors.length).eq(count);
 }
 
+export function expectWarnings(stats: any, count: number, warnings: string[] = []) {
+    stats.compilation.warnings.every(warn => {
+        const str = warn.toString();
+        expect(warnings.some(e => str.indexOf(e) !== -1), 'Warning is not covered: \n' + str).true;
+    });
+
+    expect(stats.compilation.warnings.length).eq(count);
+}
+
 export function tsconfig(
     compilerOptions?: any,
     config?: any

src/index.ts

@@ -30,6 +30,8 @@ interface Transformation {
     fresh?: boolean;
 }
 
+const DECLARATION = /\.d.ts$/i;
+
 function compiler(loader: Loader, text: string): void {
     if (loader.cacheable) {
         loader.cacheable();
@@ -44,9 +46,13 @@ function compiler(loader: Loader, text: string): void {
     const callback = loader.async();
 
     let fileName = helpers.toUnix(loader.resourcePath);
-
     instance.compiledFiles[fileName] = true;
 
+    if (DECLARATION.test(fileName)) {
+        loader.emitWarning(`[${instanceName}] TypeScript declaration files should never be required`);
+        return callback(null, '');
+    }
+
     let compiledModule;
     if (instance.loaderConfig.usePrecompiledFiles) {
         compiledModule = findCompiledModule(fileName);

src/instance.ts

@@ -41,6 +41,8 @@ export interface Loader {
     addDependency: (dep: string) => void;
     clearDependencies: () => void;
     emitFile: (fileName: string, text: string) => void;
+    emitWarning: (msg: string) => void;
+    emitError: (msg: string) => void;
     options: {
         ts?: LoaderConfig
     };