allow loaders for extensionless files

internal/bundler/bundler.go

@@ -1012,15 +1012,22 @@ func loaderFromFileExtension(extensionToLoader map[string]config.Loader, base st
 	// Pick the loader with the longest matching extension. So if there's an
 	// extension for ".css" and for ".module.css", we want to match the one for
 	// ".module.css" before the one for ".css".
-	for {
-		i := strings.IndexByte(base, '.')
-		if i == -1 {
-			break
+	if i := strings.IndexByte(base, '.'); i != -1 {
+		for {
+			if loader, ok := extensionToLoader[base[i:]]; ok {
+				return loader
+			}
+			base = base[i+1:]
+			i = strings.IndexByte(base, '.')
+			if i == -1 {
+				break
+			}
 		}
-		if loader, ok := extensionToLoader[base[i:]]; ok {
+	} else {
+		// If there's no extension, explicitly check for an extensionless loader
+		if loader, ok := extensionToLoader[""]; ok {
 			return loader
 		}
-		base = base[i+1:]
 	}
 	return config.LoaderNone
 }

internal/bundler_tests/bundler_loader_test.go

@@ -1337,3 +1337,41 @@ func TestEmptyLoaderCSS(t *testing.T) {
 		},
 	})
 }
+
+func TestExtensionlessLoaderJS(t *testing.T) {
+	loader_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				import './what'
+			`,
+			"/what": `foo()`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			Mode: config.ModeBundle,
+			ExtensionToLoader: map[string]config.Loader{
+				".js": config.LoaderJS,
+				"":    config.LoaderJS,
+			},
+		},
+	})
+}
+
+func TestExtensionlessLoaderCSS(t *testing.T) {
+	loader_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.css": `
+				@import './what';
+			`,
+			"/what": `.foo { color: red }`,
+		},
+		entryPaths: []string{"/entry.css"},
+		options: config.Options{
+			Mode: config.ModeBundle,
+			ExtensionToLoader: map[string]config.Loader{
+				".css": config.LoaderCSS,
+				"":     config.LoaderCSS,
+			},
+		},
+	})
+}

internal/bundler_tests/snapshots/snapshots_loader.txt

@@ -173,6 +173,22 @@ console.log(ns, import_c.default, void 0);
   }
 }
 
+================================================================================
+TestExtensionlessLoaderCSS
+---------- entry.css ----------
+/* what */
+.foo {
+  color: red;
+}
+
+/* entry.css */
+
+================================================================================
+TestExtensionlessLoaderJS
+---------- entry.js ----------
+// what
+foo();
+
 ================================================================================
 TestJSXAutomaticNoNameCollision
 ---------- /out.js ----------

pkg/api/api_impl.go

@@ -545,7 +545,7 @@ func validateLoaders(log logger.Log, loaders map[string]Loader) map[string]confi
 	result := bundler.DefaultExtensionToLoaderMap()
 	if loaders != nil {
 		for ext, loader := range loaders {
-			if !isValidExtension(ext) {
+			if ext != "" && !isValidExtension(ext) {
 				log.AddError(nil, logger.Range{}, fmt.Sprintf("Invalid file extension: %q", ext))
 			}
 			result[ext] = validateLoader(loader)