Add --stdin flag (#4594)

docs/user-guide/usage/cli.md

@@ -36,6 +36,10 @@ Print the configuration for the given path. stylelint outputs the configuration
 
 Only register violations for rules with an "error"-level severity (ignore "warning"-level).
 
+### `--stdin`
+
+Accept stdin input even if it is empty.
+
 ### `--version, -v`
 
 Show the currently installed version of stylelint.

lib/__tests__/cli.test.js

@@ -17,6 +17,7 @@ describe('buildCLI', () => {
 			quiet: false,
 			reportInvalidScopeDisables: false,
 			reportNeedlessDisables: false,
+			stdin: false,
 			version: false,
 		});
 	});
@@ -124,6 +125,10 @@ describe('buildCLI', () => {
 		expect(buildCLI(['--rd']).flags.reportNeedlessDisables).toBe(true);
 	});
 
+	it('flags.stdin', () => {
+		expect(buildCLI(['--stdin']).flags.stdin).toBe(true);
+	});
+
 	it('flags.stdinFilename', () => {
 		expect(buildCLI(['--stdin-filename=foo.css']).flags.stdinFilename).toBe('foo.css');
 	});

lib/cli.js

@@ -36,6 +36,7 @@ const EXIT_CODE_ERROR = 2;
  * @property {string} [ignorePattern]
  * @property {string} [noColor]
  * @property {string} [outputFile]
+ * @property {boolean} [stdin]
  * @property {string} [stdinFilename]
  * @property {boolean} [reportNeedlessDisables]
  * @property {boolean} [reportInvalidScopeDisables]
@@ -145,6 +146,10 @@ const meowOptions = {
 
         Module name or path to a JS file exporting a PostCSS-compatible syntax.
 
+      --stdin
+
+        Accept stdin input even if it is empty.
+
       --stdin-filename
 
         A filename to assign stdin input.
@@ -296,6 +301,9 @@ const meowOptions = {
 			alias: 'rd',
 			type: 'boolean',
 		},
+		stdin: {
+			type: 'boolean',
+		},
 		stdinFilename: {
 			type: 'string',
 		},
@@ -464,7 +472,7 @@ module.exports = (argv) => {
 					.catch(handleError);
 			}
 
-			if (!options.files && !options.code) {
+			if (!options.files && !options.code && !cli.flags.stdin) {
 				cli.showHelp();
 
 				return;

system-tests/cli/__snapshots__/cli.test.js.snap

@@ -62,6 +62,10 @@ exports[`CLI --help 1`] = `
 
       Module name or path to a JS file exporting a PostCSS-compatible syntax.
 
+    --stdin
+
+      Accept stdin input even if it is empty.
+
     --stdin-filename
 
       A filename to assign stdin input.

system-tests/cli/cli.test.js

@@ -77,6 +77,7 @@ describe('CLI', () => {
 				{
 					rules: {
 						'block-no-empty': [true],
+						'no-empty-source': [true],
 					},
 				},
 				null,
@@ -104,4 +105,16 @@ describe('CLI', () => {
 			expect.stringContaining('Unexpected empty block'),
 		);
 	});
+
+	it('--stdin', async () => {
+		await cli(['--stdin', '--config', path.join(__dirname, 'config.json')]);
+
+		expect(process.exitCode).toBe(2);
+
+		expect(process.stdout.write).toHaveBeenCalledTimes(1);
+		expect(process.stdout.write).toHaveBeenNthCalledWith(
+			1,
+			expect.stringContaining('Unexpected empty source'),
+		);
+	});
 });

system-tests/cli/config.json

@@ -1,5 +1,6 @@
 {
   "rules": {
-    "block-no-empty": true
+    "block-no-empty": true,
+    "no-empty-source": true
   }
 }