feat: return template

README.md

@@ -103,7 +103,12 @@ require('postcss-custom-properties-transformer')({
 		if (ctx.local.startsWith('theme-')) {
 			return ctx.local;
 		}
-		return ctx.hash('local', 4);
+
+		// You can return a template
+		return `[hash:filepath:4]-[hash:4]`;
+
+		// Alternatively, you can use the functions
+		return ctx.hash('filepath', 4) + '-' + ctx.hash(4);
 	}
 })
 ```

lib/index.js

@@ -7,10 +7,13 @@ const interpolater = require('./interpolater');
 const generateContext = require('./generate-context');
 
 const transformerWrapper = (
-	transformerFn,
+	transformer,
 	manifest = new PropertyNameManifest(),
 ) => context => {
-	let newPropertyName = transformerFn(context);
+	let newPropertyName = typeof transformer === 'function' ? transformer(context) : transformer;
+
+	newPropertyName = interpolater(newPropertyName, context);
+
 	newPropertyName = sanitizePropertyName(newPropertyName);
 
 	manifest.mark(newPropertyName, context.local);
@@ -25,17 +28,9 @@ const customPropertiesRegExp = /(^|[^\w-])var\([\W\w]+\)/;
 
 const customPropertiesTransformer = postcss.plugin('postcss-custom-properties-transformer', options => {
 	assert(options && options.transformer, '[postcss-custom-properties] a transformer must be passed in');
+	assert(['function', 'string'].includes(typeof options.transformer), `[postcss-custom-properties] Unsupported transformer type "${typeof options.transformer}"`);
 
-	let {transformer} = options;
-
-	if (typeof transformer === 'string') {
-		const template = transformer;
-		transformer = context => interpolater(template, context);
-	} else if (typeof transformer !== 'function') {
-		throw new TypeError(`[postcss-custom-properties] Unsupported transformer type "${typeof options.transformer}"`);
-	}
-
-	transformer = transformerWrapper(transformer);
+	const transformer = transformerWrapper(options.transformer);
 
 	return root => {
 		const contextMaker = generateContext(root.source.input);

test/__snapshots__/index.spec.js.snap

@@ -143,3 +143,15 @@ exports[`transformer function namespace 1`] = `
 	}
 	"
 `;
+
+exports[`transformer function return template 1`] = `
+"
+	.className {
+		--_dir_src_file_css-color: red;
+		--_dir_src_file_css-font-size: 24px;
+		background: var(--_dir_src_file_css-color);
+		border-color: var(--_dir_src_file_css-color);
+		font-size: var(--_dir_src_file_css-font-size);
+	}
+	"
+`;

test/index.spec.js

@@ -133,6 +133,16 @@ describe('transformer function', () => {
 		expect(output).toMatchSnapshot();
 	});
 
+	test('return template', async () => {
+		const output = await transform(fixtures.basicVar, {
+			transformer() {
+				return '[filepath]-[local]';
+			},
+		});
+
+		expect(output).toMatchSnapshot();
+	});
+
 	test('collision warning', async () => {
 		const warn = jest.spyOn(global.console, 'warn').mockImplementation();