Accept syntax object in customSyntax option

docs/user-guide/usage/cli.md

@@ -106,6 +106,14 @@ Using `bar/mySpecialConfig.json` as config to lint all `.css` files in the `foo`
 stylelint "foo/**/*.css" --config bar/mySpecialConfig.json
 ```
 
+### Example H - using a custom syntax
+
+Recursively linting all `.css` files in the `foo` directory using a custom syntax:
+
+```shell
+stylelint "foo/**/*.css" --customSyntax path/to/my-custom-syntax.js
+```
+
 ## Exit codes
 
 The CLI can exit the process with the following exit codes:

docs/user-guide/usage/node-api.md

@@ -150,3 +150,28 @@ stylelint
     /* .. */
   });
 ```
+
+### Example E
+
+Using a custom syntax:
+
+```js
+stylelint
+  .lint({
+    config: myConfig,
+    files: "all/my/stylesheets/*.css",
+    customSyntax: {
+      parse: (css, opts) => {
+        /* .. */
+      },
+      stringify: (root, builder) => {
+        /* .. */
+      }
+    }
+  })
+  .then(function () {
+    /* .. */
+  });
+```
+
+Note that the customSyntax option also accepts a string. [Refer to the options documentation for details](./options.md).

docs/user-guide/usage/options.md

@@ -101,17 +101,21 @@ Specify a syntax. Options:
 - `scss`
 - `sugarss`
 
-If you do not specify a syntax, stylelint automatically infer the syntaxes.
+If you do not specify a syntax, stylelint will automatically infer the syntaxes.
 
 Only use this option if you want to force a specific syntax.
 
 ## `customSyntax`
 
 CLI flag: `--custom-syntax`
 
-Module name or path to a JS file exporting a [PostCSS-compatible syntax](https://github.com/postcss/postcss#syntaxes).
+Specify a custom syntax to use on your code. Use this option if you want to force a specific syntax that's not already built into stylelint.
 
-Note, however, that stylelint can provide no guarantee that core rules work with syntaxes other than the defaults listed for the `syntax` option above.
+This option should be a string that resolves to a JS module that exports a [PostCSS-compatible syntax](https://github.com/postcss/postcss#syntaxes). The string can be a module name (like `my-module`) or a path to a JS file (like `path/to/my-module.js`).
+
+Using the Node.js API, the `customSyntax` option can also accept a [Syntax object](https://github.com/postcss/postcss/blob/abfaa7122a0f480bc5be0905df3c24a6a51a82d9/lib/postcss.d.ts#L223-L232). Stylelint treats the `parse` property as a required value.
+
+Note that stylelint can provide no guarantee that core rules work with syntaxes other than the defaults listed for the `syntax` option above.
 
 ## `disableDefaultIgnores`
 

lib/__tests__/standalone.test.js

@@ -243,7 +243,9 @@ it('unknown custom syntax option', () => {
 			throw new Error('should not have succeeded');
 		})
 		.catch((err) => {
-			expect(err.message).toBe('Cannot resolve custom syntax module unknown-module');
+			expect(err.message).toBe(
+				'Cannot resolve custom syntax module unknown-module. Check that module unknown-module is available and spelled correctly.',
+			);
 		});
 });
 

lib/getPostcssResult.js

@@ -117,24 +117,42 @@ module.exports = function (stylelint, options = {}) {
 function getCustomSyntax(customSyntax) {
 	let resolved;
 
-	try {
-		resolved = require(customSyntax);
-	} catch (error) {
-		throw new Error(`Cannot resolve custom syntax module ${customSyntax}`);
+	if (typeof customSyntax === 'string') {
+		try {
+			resolved = require(customSyntax);
+		} catch (error) {
+			throw new Error(
+				`Cannot resolve custom syntax module ${customSyntax}. Check that module ${customSyntax} is available and spelled correctly.`,
+			);
+		}
+
+		/*
+		 * PostCSS allows for syntaxes that only contain a parser, however,
+		 * it then expects the syntax to be set as the `parse` option.
+		 */
+		if (!resolved.parse) {
+			resolved = {
+				parse: resolved,
+				stringify: postcss.stringify,
+			};
+		}
+
+		return resolved;
 	}
 
-	/*
-	 * PostCSS allows for syntaxes that only contain a parser, however,
-	 * it then expects the syntax to be set as the `parse` option.
-	 */
-	if (!resolved.parse) {
-		resolved = {
-			parse: resolved,
-			stringify: postcss.stringify,
-		};
+	if (typeof customSyntax === 'object') {
+		if (typeof customSyntax.parse === 'function') {
+			resolved = { ...customSyntax };
+		} else {
+			throw new Error(
+				`An object provided to the "customSyntax" option must have a "parse" property. Ensure the "parse" property exists and its value is a function.`,
+			);
+		}
+
+		return resolved;
 	}
 
-	return resolved;
+	throw new Error(`Custom syntax must be a string or a Syntax object`);
 }
 
 /**

types/stylelint/index.d.ts

@@ -1,5 +1,5 @@
 declare module 'stylelint' {
-	import { Result, ResultMessage, WarningOptions, Warning } from 'postcss';
+	import { Result, ResultMessage, Syntax, WarningOptions, Warning } from 'postcss';
 
 	export type StylelintConfigExtends = string | Array<string>;
 	export type StylelintConfigPlugins = string | Array<string>;
@@ -90,7 +90,7 @@ declare module 'stylelint' {
 
 	export type FormatterIdentifier = 'compact' | 'json' | 'string' | 'unix' | 'verbose' | Formatter;
 
-	export type CustomSyntax = string;
+	export type CustomSyntax = string | Syntax;
 
 	export type StylelintOptions = {
 		config?: StylelintConfig;