fix!: Behavior of CLI when no arguments are passed

docs/src/use/command-line-interface.md

@@ -36,6 +36,15 @@ Please note that when passing a glob as a parameter, it is expanded by your shel
 npx eslint "lib/**"
 ```
 
+If you are using a [flat configuration file](./configure/configuration-files-new) (`eslint.config.js`), you can also omit the file arguments and ESLint will use `.`. For instance, these two lines perform the same operation:
+
+```shell
+npx eslint .
+npx eslint
+```
+
+If you are not using a flat configuration file, running ESLint without file arguments results in an error.
+
 **Note:** You can also use alternative package managers such as [Yarn](https://yarnpkg.com/) or [pnpm](https://pnpm.io/) to run ESLint. Please refer to your package manager's documentation for the correct syntax.
 
 ## Pass Multiple Values to an Option
@@ -112,6 +121,7 @@ Miscellaneous:
   --no-error-on-unmatched-pattern  Prevent errors when pattern is unmatched
   --exit-on-fatal-error           Exit with exit code 2 in case of fatal error - default: false
   --no-warn-ignored               Suppress warnings when the file list includes ignored files. *Flat Config Mode Only*
+  --pass-on-no-patterns           Exit with exit code 0 in case no file patterns are passed
   --debug                         Output debugging information
   -h, --help                      Show help
   -v, --version                   Output the version number
@@ -734,6 +744,18 @@ npx eslint --exit-on-fatal-error file.js
 npx eslint --no-warn-ignored --max-warnings 0 ignored-file.js
 ```
 
+#### `--pass-on-no-patterns`
+
+This option allows ESLint to exit with code 0 when no file or directory patterns are passed. Without this option, ESLint assumes you want to use `.` as the pattern. (When running in legacy eslintrc mode, ESLint will exit with code 1.)
+
+* **Argument Type**: No argument.
+
+##### `--pass-on-no-patterns` example
+
+```shell
+npx eslint --pass-on-no-patterns
+```
+
 #### `--debug`
 
 This option outputs debugging information to the console. Add this flag to an ESLint command line invocation in order to get extra debugging information while the command runs.

lib/cli.js

@@ -94,7 +94,8 @@ async function translateOptions({
     resolvePluginsRelativeTo,
     rule,
     rulesdir,
-    warnIgnored
+    warnIgnored,
+    passOnNoPatterns
 }, configType) {
 
     let overrideConfig, overrideConfigFile;
@@ -187,7 +188,8 @@ async function translateOptions({
         fixTypes: fixType,
         ignore,
         overrideConfig,
-        overrideConfigFile
+        overrideConfigFile,
+        passOnNoPatterns
     };
 
     if (configType === "flat") {

lib/eslint/eslint-helpers.js

@@ -105,20 +105,30 @@ class AllFilesIgnoredError extends Error {
 
 /**
  * Check if a given value is a non-empty string or not.
- * @param {any} x The value to check.
- * @returns {boolean} `true` if `x` is a non-empty string.
+ * @param {any} value The value to check.
+ * @returns {boolean} `true` if `value` is a non-empty string.
  */
-function isNonEmptyString(x) {
-    return typeof x === "string" && x.trim() !== "";
+function isNonEmptyString(value) {
+    return typeof value === "string" && value.trim() !== "";
 }
 
 /**
  * Check if a given value is an array of non-empty strings or not.
- * @param {any} x The value to check.
- * @returns {boolean} `true` if `x` is an array of non-empty strings.
+ * @param {any} value The value to check.
+ * @returns {boolean} `true` if `value` is an array of non-empty strings.
  */
-function isArrayOfNonEmptyString(x) {
-    return Array.isArray(x) && x.every(isNonEmptyString);
+function isArrayOfNonEmptyString(value) {
+    return Array.isArray(value) && value.length && value.every(isNonEmptyString);
+}
+
+/**
+ * Check if a given value is an empty array or an array of non-empty strings.
+ * @param {any} value The value to check.
+ * @returns {boolean} `true` if `value` is an empty array or an array of non-empty
+ *      strings.
+ */
+function isEmptyArrayOrArrayOfNonEmptyString(value) {
+    return Array.isArray(value) && value.every(isNonEmptyString);
 }
 
 //-----------------------------------------------------------------------------
@@ -676,6 +686,7 @@ function processOptions({
     overrideConfigFile = null,
     plugins = {},
     warnIgnored = true,
+    passOnNoPatterns = false,
     ...unknownOptions
 }) {
     const errors = [];
@@ -759,7 +770,7 @@ function processOptions({
     if (typeof ignore !== "boolean") {
         errors.push("'ignore' must be a boolean.");
     }
-    if (!isArrayOfNonEmptyString(ignorePatterns) && ignorePatterns !== null) {
+    if (!isEmptyArrayOrArrayOfNonEmptyString(ignorePatterns) && ignorePatterns !== null) {
         errors.push("'ignorePatterns' must be an array of non-empty strings or null.");
     }
     if (typeof overrideConfig !== "object") {
@@ -768,6 +779,9 @@ function processOptions({
     if (!isNonEmptyString(overrideConfigFile) && overrideConfigFile !== null && overrideConfigFile !== true) {
         errors.push("'overrideConfigFile' must be a non-empty string, null, or true.");
     }
+    if (typeof passOnNoPatterns !== "boolean") {
+        errors.push("'passOnNoPatterns' must be a boolean.");
+    }
     if (typeof plugins !== "object") {
         errors.push("'plugins' must be an object or null.");
     } else if (plugins !== null && Object.keys(plugins).includes("")) {
@@ -800,6 +814,7 @@ function processOptions({
         globInputPaths,
         ignore,
         ignorePatterns,
+        passOnNoPatterns,
         warnIgnored
     };
 }

lib/eslint/eslint.js

@@ -67,6 +67,8 @@ const { version } = require("../../package.json");
  * @property {string} [resolvePluginsRelativeTo] The folder where plugins should be resolved from, defaulting to the CWD.
  * @property {string[]} [rulePaths] An array of directories to load custom rules from.
  * @property {boolean} [useEslintrc] False disables looking for .eslintrc.* files.
+ * @property {boolean} [passOnNoPatterns=false] When set to true, missing patterns cause
+ *      the linting operation to short circuit and not report any failures.
  */
 
 /**
@@ -97,38 +99,48 @@ const privateMembersMap = new WeakMap();
 
 /**
  * Check if a given value is a non-empty string or not.
- * @param {any} x The value to check.
- * @returns {boolean} `true` if `x` is a non-empty string.
+ * @param {any} value The value to check.
+ * @returns {boolean} `true` if `value` is a non-empty string.
  */
-function isNonEmptyString(x) {
-    return typeof x === "string" && x.trim() !== "";
+function isNonEmptyString(value) {
+    return typeof value === "string" && value.trim() !== "";
 }
 
 /**
  * Check if a given value is an array of non-empty strings or not.
- * @param {any} x The value to check.
- * @returns {boolean} `true` if `x` is an array of non-empty strings.
+ * @param {any} value The value to check.
+ * @returns {boolean} `true` if `value` is an array of non-empty strings.
  */
-function isArrayOfNonEmptyString(x) {
-    return Array.isArray(x) && x.every(isNonEmptyString);
+function isArrayOfNonEmptyString(value) {
+    return Array.isArray(value) && value.length && value.every(isNonEmptyString);
+}
+
+/**
+ * Check if a given value is an empty array or an array of non-empty strings.
+ * @param {any} value The value to check.
+ * @returns {boolean} `true` if `value` is an empty array or an array of non-empty
+ *      strings.
+ */
+function isEmptyArrayOrArrayOfNonEmptyString(value) {
+    return Array.isArray(value) && value.every(isNonEmptyString);
 }
 
 /**
  * Check if a given value is a valid fix type or not.
- * @param {any} x The value to check.
- * @returns {boolean} `true` if `x` is valid fix type.
+ * @param {any} value The value to check.
+ * @returns {boolean} `true` if `value` is valid fix type.
  */
-function isFixType(x) {
-    return x === "directive" || x === "problem" || x === "suggestion" || x === "layout";
+function isFixType(value) {
+    return value === "directive" || value === "problem" || value === "suggestion" || value === "layout";
 }
 
 /**
  * Check if a given value is an array of fix types or not.
- * @param {any} x The value to check.
- * @returns {boolean} `true` if `x` is an array of fix types.
+ * @param {any} value The value to check.
+ * @returns {boolean} `true` if `value` is an array of fix types.
  */
-function isFixTypeArray(x) {
-    return Array.isArray(x) && x.every(isFixType);
+function isFixTypeArray(value) {
+    return Array.isArray(value) && value.every(isFixType);
 }
 
 /**
@@ -169,6 +181,7 @@ function processOptions({
     resolvePluginsRelativeTo = null, // ← should be null by default because if it's a string then it suppresses RFC47 feature.
     rulePaths = [],
     useEslintrc = true,
+    passOnNoPatterns = false,
     ...unknownOptions
 }) {
     const errors = [];
@@ -225,7 +238,7 @@ function processOptions({
     if (typeof errorOnUnmatchedPattern !== "boolean") {
         errors.push("'errorOnUnmatchedPattern' must be a boolean.");
     }
-    if (!isArrayOfNonEmptyString(extensions) && extensions !== null) {
+    if (!isEmptyArrayOrArrayOfNonEmptyString(extensions) && extensions !== null) {
         errors.push("'extensions' must be an array of non-empty strings or null.");
     }
     if (typeof fix !== "boolean" && typeof fix !== "function") {
@@ -271,12 +284,15 @@ function processOptions({
     ) {
         errors.push("'resolvePluginsRelativeTo' must be a non-empty string or null.");
     }
-    if (!isArrayOfNonEmptyString(rulePaths)) {
+    if (!isEmptyArrayOrArrayOfNonEmptyString(rulePaths)) {
         errors.push("'rulePaths' must be an array of non-empty strings.");
     }
     if (typeof useEslintrc !== "boolean") {
         errors.push("'useEslintrc' must be a boolean.");
     }
+    if (typeof passOnNoPatterns !== "boolean") {
+        errors.push("'passOnNoPatterns' must be a boolean.");
+    }
 
     if (errors.length > 0) {
         throw new ESLintInvalidOptionsError(errors);
@@ -300,7 +316,8 @@ function processOptions({
         reportUnusedDisableDirectives,
         resolvePluginsRelativeTo,
         rulePaths,
-        useEslintrc
+        useEslintrc,
+        passOnNoPatterns
     };
 }
 
@@ -541,10 +558,15 @@ class ESLint {
      * @returns {Promise<LintResult[]>} The results of linting the file patterns given.
      */
     async lintFiles(patterns) {
+        const { cliEngine, options } = privateMembersMap.get(this);
+
+        if (options.passOnNoPatterns && (patterns === "" || (Array.isArray(patterns) && patterns.length === 0))) {
+            return [];
+        }
+
         if (!isNonEmptyString(patterns) && !isArrayOfNonEmptyString(patterns)) {
             throw new Error("'patterns' must be a non-empty string or an array of non-empty strings");
         }
-        const { cliEngine } = privateMembersMap.get(this);
 
         return processCLIEngineLintReport(
             cliEngine,

lib/eslint/flat-eslint.js

@@ -85,6 +85,8 @@ const LintResultCache = require("../cli-engine/lint-result-cache");
  *      when a string.
  * @property {Record<string,Plugin>} [plugins] An array of plugin implementations.
  * @property {boolean} warnIgnored Show warnings when the file list includes ignored files
+ * @property {boolean} [passOnNoPatterns=false] When set to true, missing patterns cause
+ *      the linting operation to short circuit and not report any failures.
  */
 
 //------------------------------------------------------------------------------
@@ -738,16 +740,46 @@ class FlatESLint {
      * @returns {Promise<LintResult[]>} The results of linting the file patterns given.
      */
     async lintFiles(patterns) {
-        if (!isNonEmptyString(patterns) && !isArrayOfNonEmptyString(patterns)) {
-            throw new Error("'patterns' must be a non-empty string or an array of non-empty strings");
-        }
 
+        let normalizedPatterns = patterns;
         const {
             cacheFilePath,
             lintResultCache,
             linter,
             options: eslintOptions
         } = privateMembers.get(this);
+
+        /*
+         * Special cases:
+         * 1. `patterns` is an empty string
+         * 2. `patterns` is an empty array
+         *
+         * In both cases, we use the cwd as the directory to lint.
+         */
+        if (patterns === "" || Array.isArray(patterns) && patterns.length === 0) {
+
+            /*
+             * Special case: If `passOnNoPatterns` is true, then we just exit
+             * without doing any work.
+             */
+            if (eslintOptions.passOnNoPatterns) {
+                return [];
+            }
+
+            normalizedPatterns = ["."];
+        } else {
+
+            if (!isNonEmptyString(patterns) && !isArrayOfNonEmptyString(patterns)) {
+                throw new Error("'patterns' must be a non-empty string or an array of non-empty strings");
+            }
+
+            if (typeof patterns === "string") {
+                normalizedPatterns = [patterns];
+            }
+        }
+
+        debug(`Using file patterns: ${normalizedPatterns}`);
+
         const configs = await calculateConfigArray(this, eslintOptions);
         const {
             allowInlineConfig,
@@ -779,7 +811,7 @@ class FlatESLint {
         }
 
         const filePaths = await findFiles({
-            patterns: typeof patterns === "string" ? [patterns] : patterns,
+            patterns: normalizedPatterns,
             cwd,
             globInputPaths,
             configs,

lib/options.js

@@ -57,6 +57,8 @@ const optionator = require("optionator");
  * @property {boolean} quiet Report errors only
  * @property {boolean} [version] Output the version number
  * @property {boolean} warnIgnored Show warnings when the file list includes ignored files
+ * @property {boolean} [passOnNoPatterns=false] When set to true, missing patterns cause
+ *      the linting operation to short circuit and not report any failures.
  * @property {string[]} _ Positional filenames or patterns
  */
 
@@ -370,6 +372,12 @@ module.exports = function(usingFlatConfig) {
                 description: "Exit with exit code 2 in case of fatal error"
             },
             warnIgnoredFlag,
+            {
+                option: "pass-on-no-patterns",
+                type: "Boolean",
+                default: false,
+                description: "Exit with exit code 0 in case no file patterns are passed"
+            },
             {
                 option: "debug",
                 type: "Boolean",

tests/lib/cli.js

@@ -814,6 +814,13 @@ describe("cli", () => {
                         assert.strictEqual(exit, useFlatConfig ? 0 : 2);
                     });
 
+                    it(`should not lint anything when no files are passed if --pass-on-no-patterns is passed with configType:${configType}`, async () => {
+                        const exit = await cli.execute("--pass-on-no-patterns", null, useFlatConfig);
+
+                        assert.isFalse(log.info.called);
+                        assert.strictEqual(exit, 0);
+                    });
+
                     it(`should suppress the warning if --no-warn-ignored is passed and an ignored file is passed via stdin with configType:${configType}`, async () => {
                         const options = useFlatConfig
                             ? `--config ${getFixturePath("eslint.config_with_ignores.js")}`