Fix ConfigurationError regression for custom syntaxes (#9245)

jeddy3 · web-flow · commit 20f6e9de1035 · 2026-04-27T09:35:08.000+01:00
diff --git a/.changeset/silent-carpets-repeat.md b/.changeset/silent-carpets-repeat.md
@@ -0,0 +1,5 @@
+---
+"stylelint": patch
+---
+
+Fixed: `ConfigurationError` regression for custom syntaxes
diff --git a/lib/__tests__/standalone-syntax.test.mjs b/lib/__tests__/standalone-syntax.test.mjs
@@ -1,4 +1,6 @@
-import { writeFile } from 'node:fs/promises';
+import { mkdtemp, rm, writeFile } from 'node:fs/promises';
+import { join } from 'node:path';
+import { tmpdir } from 'node:os';
 
 import replaceBackslashes from '../testUtils/replaceBackslashes.mjs';
 import standalone from '../standalone.mjs';
@@ -137,7 +139,7 @@ it('rejects on unknown custom syntax option', async () => {
 			config: config(),
 		}),
 	).rejects.toThrow(
-		'Could not find "unknown-module". Do you need to install the package or use the "configBasedir" option?',
+		'Cannot resolve custom syntax module "unknown-module". Check that module "unknown-module" is available and spelled correctly.',
 	);
 });
 
@@ -178,6 +180,26 @@ describe('customSyntax set in the config', () => {
 		expect(results[0].warnings[0]).toMatchObject({ line: 2, column: 3, rule: 'block-no-empty' });
 	});
 
+	it('standalone with bare-package custom syntax not reachable from configBasedir or cwd', async () => {
+		const isolatedDir = await mkdtemp(join(tmpdir(), 'stylelint-isolated-'));
+
+		try {
+			const { results } = await standalone({
+				config: config({ customSyntax: 'postcss-scss' }),
+				configBasedir: isolatedDir,
+				cwd: isolatedDir,
+				code: '$foo: bar; // foo;\nb {}',
+				formatter: stringFormatter,
+			});
+
+			expect(results).toHaveLength(1);
+			expect(results[0].warnings).toHaveLength(1);
+			expect(results[0].warnings[0]).toMatchObject({ line: 2, column: 3, rule: 'block-no-empty' });
+		} finally {
+			await rm(isolatedDir, { recursive: true, force: true });
+		}
+	});
+
 	it('standalone with custom syntax as npm package', async () => {
 		const { results } = await standalone({
 			config: config({ customSyntax: await import('postcss-scss') }),
@@ -234,7 +256,7 @@ describe('customSyntax set in the config', () => {
 				config: config({ customSyntax: 'unknown-module' }),
 			}),
 		).rejects.toThrow(
-			'Could not find "unknown-module". Do you need to install the package or use the "configBasedir" option?',
+			'Cannot resolve custom syntax module "unknown-module". Check that module "unknown-module" is available and spelled correctly.',
 		);
 	});
 
diff --git a/lib/augmentConfig.mjs b/lib/augmentConfig.mjs
@@ -35,6 +35,14 @@ function absolutizeGlob(glob, basedir) {
 	return normalizePath(result);
 }
 
+/**
+ * @param {string} lookup
+ * @returns {boolean}
+ */
+function isPathLike(lookup) {
+	return lookup.startsWith('./') || lookup.startsWith('../') || isAbsolute(lookup);
+}
+
 /**
  * - Merges config and stylelint options
  * - Makes all paths absolute
@@ -187,7 +195,7 @@ function absolutizePaths(config, configDir, cwd) {
 		config.processors = config.processors.map(toAbsolutePath);
 	}
 
-	if (isString(config.customSyntax)) {
+	if (isString(config.customSyntax) && isPathLike(config.customSyntax)) {
 		config.customSyntax = getModulePath(configDir, config.customSyntax, cwd);
 	}
 
@@ -200,9 +208,10 @@ function absolutizePaths(config, configDir, cwd) {
 			if (isObject(entry)) {
 				return {
 					files: [entry.files].flat().map((glob) => absolutizeGlob(glob, configDir)),
-					customSyntax: isString(entry.customSyntax)
-						? getModulePath(configDir, entry.customSyntax, cwd)
-						: entry.customSyntax,
+					customSyntax:
+						isString(entry.customSyntax) && isPathLike(entry.customSyntax)
+							? getModulePath(configDir, entry.customSyntax, cwd)
+							: entry.customSyntax,
 				};
 			}
 

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +"stylelint": patch
 +---
++
 +Fixed: `ConfigurationError` regression for custom syntaxes