Add support for --fix-to-stdout

This option was lost in the recent rewrite.

README.md

@@ -37,6 +37,7 @@
 - Automatically starts, stops and restarts the background server.
 - Binds to parent process, editor process or exits after IDLE time.
 - Falls back to bundled eslint if local eslint is missing.
+- Prints fixed file on stdout with `--fix-to-stdout`
 
 ## Setup
 
@@ -108,6 +109,7 @@ 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 +154,7 @@ 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 +179,5 @@ 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

@@ -24,15 +24,35 @@ const DAEMON_TERMINATION_CODE_REGEXP = new RegExp(
  * @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 -- not quite sure which execution flow could be problematic here
+      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,
     JSON.stringify(process.cwd()),
-    JSON.stringify(process.argv)
+    JSON.stringify(eslint_args)
   ];
   socket.write(args.join(' '));
   if (text) {
@@ -48,7 +68,10 @@ export async function forwardToDaemon(resolver, config) {
       let chunk = '';
       while ((chunk = socket.read()) !== null) {
         content += chunk;
-        if (content.length > DAEMON_TERMINATION_CODE_MAX_LENGTH) {
+        if (
+          !fix_to_stdout &&
+          content.length > DAEMON_TERMINATION_CODE_MAX_LENGTH
+        ) {
           const message_length =
             content.length - DAEMON_TERMINATION_CODE_MAX_LENGTH;
           // write everything we are sure doesn't contain the termination code:
@@ -78,6 +101,11 @@ export async function forwardToDaemon(resolver, config) {
 
       process.exitCode = Number(match[1]);
 
+      if (fix_to_stdout) {
+        const object = JSON.parse(content);
+        content = object[0].output || text;
+      }
+
       if (content) {
         process.stdout.write(content);
       }

lib/forwarder.test.js

@@ -225,5 +225,19 @@ 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
 

test/test.integration.js

@@ -67,7 +67,7 @@ describe('integration tests', () => {
     });
   });
 
-  [SUPPORTED_ESLINT_VERSIONS].forEach((fixture) => {
+  SUPPORTED_ESLINT_VERSIONS.forEach((fixture) => {
     context(fixture, () => {
       const cwd = path.resolve(`test/fixture/${fixture}`);
       const { version: eslint_version } = require(
@@ -176,4 +176,103 @@ describe('integration tests', () => {
       });
     });
   });
+
+  context('--fix-to-stdout', () => {
+    SUPPORTED_ESLINT_VERSIONS.filter(
+      (fixture) => fixture !== 'v4.0.x' // v4 misses --fix-dry-run
+    ).forEach((fixture) => {
+      context(fixture, () => {
+        const cwd = path.resolve(`test/fixture/${fixture}`);
+        const config = `${cwd}/node_modules/eslint/.eslint_d`;
+
+        beforeEach(async () => {
+          await killDaemon();
+          await startDaemon();
+        });
+
+        afterEach(killDaemon);
+
+        const run_args = `--fix-to-stdout --stdin --stdin-filename ${cwd}/../foo.js`;
+
+        context('when file only contains fixable problems', () => {
+          it('prints input if no change is needed', async () => {
+            const stdin = `console.log('Hello eslint');`;
+            const { error, stdout, stderr } = await run(run_args, {
+              cwd,
+              stdin
+            });
+
+            assert.equals(stdout, stdin);
+            assert.equals(stderr, '');
+            assert.isNull(error);
+          });
+
+          it('prints fixed output if change is needed', async () => {
+            const { error, stdout, stderr } = await run(run_args, {
+              cwd,
+              stdin: `console.log("Hello eslint");`
+            });
+
+            assert.equals(stdout, `console.log('Hello eslint');`);
+            assert.equals(stderr, '');
+            assert.isNull(error);
+          });
+        });
+
+        context('when file contains non-fixable problems', () => {
+          it('prints input if no change is needed', async () => {
+            const stdin = `/* eslint radix: "error" */
+            console.log('Hello' + parseInt('087'))`;
+
+            const { error, stdout, stderr } = await run(run_args, {
+              cwd,
+              stdin
+            });
+
+            assert.equals(
+              stdout,
+              `/* eslint radix: "error" */
+            console.log('Hello' + parseInt('087'))`
+            );
+            assert.equals(stderr, '');
+            refute.isNull(error);
+            assert.equals(error?.['code'], 1);
+          });
+
+          it('prints fixed output if change is needed', async () => {
+            const stdin = `/* eslint radix: "error" */
+            console.log("Hello" + parseInt('087'))`;
+
+            const { error, stdout, stderr } = await run(run_args, {
+              cwd,
+              stdin
+            });
+
+            assert.equals(
+              stdout,
+              `/* eslint radix: "error" */
+            console.log('Hello' + parseInt('087'))`
+            );
+            assert.equals(stderr, '');
+            refute.isNull(error);
+            assert.equals(error?.['code'], 1);
+          });
+        });
+
+        async function killDaemon() {
+          try {
+            const raw = await fs.readFile(config, 'utf8');
+            const [, , pid] = raw.split(' ');
+            process.kill(Number(pid), 0);
+          } catch {
+            // nothing to kill
+          }
+        }
+
+        async function startDaemon() {
+          await run('start', { cwd });
+        }
+      });
+    });
+  });
 });