Support shorthand syntax for type assertions

src/rollup/types.d.ts

@@ -566,7 +566,10 @@ export type OptionsPaths = Record<string, string> | ((id: string) => string);
 
 type GetExternalImportAssertions = (moduleInfo: ModuleInfo) => Record<string, string> | null | void;
 
-type ExternalImportAssertionsOption = GetExternalImportAssertions | false;
+type ExternalImportAssertionsOption =
+	| GetExternalImportAssertions
+	| false
+	| Record<string, string | null>;
 
 export type InteropType = 'compat' | 'auto' | 'esModule' | 'default' | 'defaultOnly';
 

src/utils/options/normalizeOutputOptions.ts

@@ -8,7 +8,7 @@ import type {
 } from '../../rollup/types';
 import { ensureArray } from '../ensureArray';
 import { errInvalidExportOptionValue, errInvalidOption, error, warnDeprecation } from '../error';
-import { resolve } from '../path';
+import { extname, resolve } from '../path';
 import { sanitizeFileName as defaultSanitizeFileName } from '../sanitizeFileName';
 import { isValidUrl } from '../url';
 import {
@@ -355,6 +355,8 @@ function getExports(
 	return configExports || 'auto';
 }
 
+const defaultAssertions = { '.json': 'json' };
+
 function getExternalImportAssertions(
 	config: OutputOptions
 ): NormalizedOutputOptions['externalImportAssertions'] {
@@ -365,7 +367,11 @@ function getExternalImportAssertions(
 	if (configExternalImportAssertions === false) {
 		return () => null;
 	}
-	return ({ id }) => (id.endsWith('.json') ? { type: 'json' } : null);
+	const typeAssertions = configExternalImportAssertions || defaultAssertions;
+	return ({ id }) => {
+		const type = typeAssertions[extname(id)];
+		return type ? { type } : null;
+	};
 }
 
 const getGeneratedCode = (

test/form/samples/import-assertions/assertion-type-via-extension/_config.js

@@ -0,0 +1,15 @@
+module.exports = {
+	description: 'allows to configure the "type" assertion via a shorthand',
+	options: {
+		external: true,
+		output: {
+			name: 'bundle',
+			externalImportAssertions: {
+				'.json': null,
+				'.css': 'css',
+				'.foo': 'special',
+				'': 'empty'
+			}
+		}
+	}
+};

test/form/samples/import-assertions/assertion-type-via-extension/_expected.js

@@ -0,0 +1,11 @@
+import 'external.json';
+import 'external.css' assert { type: 'css' };
+import 'external.foo' assert { type: 'special' };
+import 'external' assert { type: 'empty' };
+import 'external.ignored';
+
+import('external.json');
+import('external.css', { assert: { type: 'css' } });
+import('external.foo', { assert: { type: 'special' } });
+import('external', { assert: { type: 'empty' } });
+import('external.ignored');

test/form/samples/import-assertions/assertion-type-via-extension/main.js

@@ -0,0 +1,11 @@
+import 'external.json';
+import 'external.css';
+import 'external.foo';
+import 'external';
+import 'external.ignored';
+
+import('external.json');
+import('external.css');
+import('external.foo');
+import('external');
+import('external.ignored');