Add support for --fix-to-stdout

This option was lost in the recent rewrite.

README.md

@@ -108,6 +108,7 @@ All arguments are passed to eslint, except for the following commands:
   status          Show daemon status, process id and resolved eslint version
   --help, -h      Show this help
   --version, -v   Show version number of eslint_d and bundled eslint
+  --fix-to-stdout Print fixed file to stdout (requires --stdin)
 ```
 
 ## Environment variables
@@ -152,7 +153,7 @@ changed: `package.json`, `package-lock.json`, `npm-shrinkwrap.json`,
 
 ## Compatibility
 
-- `14.0.0`: eslint 4 - 9, node 18 - 22 (ships with eslint 9)
+- `14.0.0`: eslint 4 - 9, node 18 - 22 (ships with eslint 9) (see [^1])
 - `13.0.0`: eslint 4 - 8, node 12 - 20 (ships with eslint 8)
 - `12.0.0`: eslint 4 - 8, node 12 - 16 (ships with eslint 8)
 - `11.0.0`: eslint 4 - 8, node 12 - 16 (ships with eslint 7)
@@ -177,3 +178,5 @@ MIT
 [syntastic]: https://github.com/scrooloose/syntastic
 [flycheck]: http://www.flycheck.org/
 [SublimeLinter-eslint]: https://github.com/SublimeLinter/SublimeLinter-eslint
+
+[^1]: The support for `--fix-to-stdout` is only provided with eslint 5 and beyond.

lib/forwarder.js

@@ -15,15 +15,35 @@ const EXIT_TOKEN_LENGTH = 7;
  * @param {Config} config
  */
 export async function forwardToDaemon(resolver, config) {
+  const eslint_args = process.argv.slice();
   const text = process.argv.includes('--stdin') ? await readStdin() : null;
   const { stdout } = supportsColor;
 
+  const fix_to_stdout_index = eslint_args.indexOf('--fix-to-stdout');
+  const fix_to_stdout = fix_to_stdout_index !== -1;
+
+  if (fix_to_stdout) {
+    if (!eslint_args.includes('--stdin')) {
+      console.error('--fix-to-stdout requires passing --stdin as well');
+      // eslint-disable-next-line require-atomic-updates
+      process.exitCode = 1;
+      return;
+    }
+    eslint_args.splice(
+      fix_to_stdout_index,
+      1,
+      '--fix-dry-run',
+      '--format',
+      'json'
+    );
+  }
+
   const socket = net.connect(config.port, '127.0.0.1');
   const args = [
     config.token,
     stdout ? stdout.level : 0,
     process.cwd(),
-    process.argv
+    eslint_args
   ];
   socket.write(JSON.stringify(args));
   if (text) {
@@ -39,16 +59,17 @@ export async function forwardToDaemon(resolver, config) {
       let chunk = '';
       while ((chunk = socket.read()) !== null) {
         content += chunk;
-        if (content.length > EXIT_TOKEN_LENGTH) {
-          const message_length = content.length - EXIT_TOKEN_LENGTH;
-          // Write everything we are sure doesn't contain the termination code:
-          process.stdout.write(content.substring(0, message_length));
-          // Keep only what we haven't written yet:
-          content = content.substring(message_length);
+        if (!fix_to_stdout && content.length > EXIT_TOKEN_LENGTH) {
+          process.stdout.write(flushMessage());
         }
       }
     })
     .on('end', () => {
+      if (fix_to_stdout) {
+        const { output } = JSON.parse(flushMessage())[0];
+        process.stdout.write(output || text);
+      }
+
       // The remaining 'content' must be the termination code:
       const match = content.match(EXIT_TOKEN_REGEXP);
       if (match) {
@@ -69,6 +90,18 @@ export async function forwardToDaemon(resolver, config) {
       }
       process.exitCode = 1;
     });
+
+  /**
+   * @returns {string}
+   */
+  function flushMessage() {
+    const message_length = content.length - EXIT_TOKEN_LENGTH;
+    // Extract everything we are sure doesn't contain the termination code:
+    const message = content.substring(0, message_length);
+    // Keep only what we haven't written yet:
+    content = content.substring(message_length);
+    return message;
+  }
 }
 
 function readStdin() {

lib/forwarder.test.js

@@ -222,5 +222,19 @@ describe('lib/forwarder', () => {
       assert.equals(process.exitCode, 1);
       assert.calledOnceWith(fs.unlink, `${resolver.base}/.eslint_d`);
     });
+
+    context('--fix-to-stdout', () => {
+      it('throws if --stdin is absent', async () => {
+        argv.push('--fix-to-stdout');
+
+        await forwardToDaemon(resolver, config);
+
+        assert.equals(process.exitCode, 1);
+        assert.calledOnceWith(
+          console.error,
+          '--fix-to-stdout requires passing --stdin as well'
+        );
+      });
+    });
   });
 });

lib/help.js

@@ -7,6 +7,7 @@ All arguments are passed to eslint, except for the following commands:
   stop            Stop the daemon
   restart         Restart the daemon
   status          Show daemon status, process id and resolved eslint version
+  --fix-to-stdout Print fixed file to stdout (requires --stdin)
   --help, -h      Show this help
   --version, -v   Show version number of eslint_d and bundled eslint