Allow linting specific files, and support --printConfig

scripts/run-eslint.ts

@@ -42,13 +42,26 @@ main().catch((error) => {
  * The entrypoint to this script.
  */
 async function main() {
-  const { cache, fix, quiet } = parseCommandLineArguments();
+  const parsedArguments = parseCommandLineArguments();
+  const { cache, fix, printConfig, quiet, files: givenFiles } = parsedArguments;
+  const files = givenFiles.length > 0 ? givenFiles : ['.'];
 
   const eslint = new ESLint({ cache, fix });
-  const results = await runESLint(eslint, { fix, quiet });
+
+  if (printConfig) {
+    if (files.length > 1) {
+      throw new Error('Must pass only one file to pass --printConfig');
+    }
+
+    const config = await eslint.calculateConfigForFile(files[0]);
+    console.log(JSON.stringify(config, null, '  '));
+    return;
+  }
+
+  const results = await lintFiles(eslint, files, { fix, quiet });
   const hasErrors = results.some((result) => result.errorCount > 0);
 
-  if (!quiet && !hasErrors) {
+  if (files.length === 0 && !quiet && !hasErrors) {
     evaluateWarnings(results);
   }
 }
@@ -59,7 +72,13 @@ async function main() {
  * @returns The parsed arguments.
  */
 function parseCommandLineArguments() {
-  return yargs(process.argv.slice(2))
+  const {
+    cache,
+    fix,
+    printConfig,
+    quiet,
+    _: rest,
+  } = yargs(process.argv.slice(2))
     .option('cache', {
       type: 'boolean',
       description: 'Cache results to speed up future runs',
@@ -70,30 +89,53 @@ function parseCommandLineArguments() {
       description: 'Automatically fix problems',
       default: false,
     })
+    .option('printConfig', {
+      type: 'boolean',
+      description:
+        'Print the configuration used for the given file rather than running lint rules',
+      default: false,
+    })
     .option('quiet', {
       type: 'boolean',
       description:
         'Only report errors, disabling the warnings quality gate in the process',
       default: false,
     })
-    .help().argv;
+    .help()
+    .string('_').argv;
+
+  // Type assertion: yargs' types incorrectly type `_`.
+  const files = rest as string[];
+
+  return {
+    cache,
+    files,
+    fix,
+    printConfig,
+    quiet,
+  };
 }
 
 /**
  * Runs ESLint on the project files.
  *
  * @param eslint - The ESLint instance.
+ * @param files - The files to lint.
  * @param options - The options for running ESLint.
- * @param options.quiet - Whether to only report errors (true) or not (false).
  * @param options.fix - Whether to automatically fix problems (true) or not
  * (false).
+ * @param options.quiet - Whether to only report errors (true) or not (false).
  * @returns A promise that resolves to the lint results.
  */
-async function runESLint(
+async function lintFiles(
   eslint: ESLint,
-  options: { quiet: boolean; fix: boolean },
+  files: string[],
+  options: {
+    fix: boolean;
+    quiet: boolean;
+  },
 ): Promise<ESLint.LintResult[]> {
-  let results = await eslint.lintFiles(['.']);
+  let results = await eslint.lintFiles(files);
   const errorResults = ESLint.getErrorResults(results);
 
   if (errorResults.length > 0) {