feat!: Switch Linter to flat config by default (#17851)

* feat!: Switch Linter to flat config by default

Refs #13481

* Fix failing tests

* Fix fuzzer

* Ensure verify() defaults to flat config

lib/cli-engine/cli-engine.js

@@ -650,7 +650,7 @@ class CLIEngine {
         });
         const lintResultCache =
             options.cache ? new LintResultCache(cacheFilePath, options.cacheStrategy) : null;
-        const linter = new Linter({ cwd: options.cwd });
+        const linter = new Linter({ cwd: options.cwd, configType: "eslintrc" });
 
         /** @type {ConfigArray[]} */
         const lastConfigArrays = [configArrayFactory.getConfigArrayForFile()];

lib/linter/linter.js

@@ -1172,9 +1172,9 @@ class Linter {
      * Initialize the Linter.
      * @param {Object} [config] the config object
      * @param {string} [config.cwd] path to a directory that should be considered as the current working directory, can be undefined.
-     * @param {"flat"|"eslintrc"} [config.configType="eslintrc"] the type of config used.
+     * @param {"flat"|"eslintrc"} [config.configType="flat"] the type of config used.
      */
-    constructor({ cwd, configType } = {}) {
+    constructor({ cwd, configType = "flat" } = {}) {
         internalSlotsMap.set(this, {
             cwd: normalizeCwd(cwd),
             lastConfigArray: null,
@@ -1368,29 +1368,29 @@ class Linter {
             ? { filename: filenameOrOptions }
             : filenameOrOptions || {};
 
-        if (config) {
-            if (configType === "flat") {
-
-                /*
-                 * Because of how Webpack packages up the files, we can't
-                 * compare directly to `FlatConfigArray` using `instanceof`
-                 * because it's not the same `FlatConfigArray` as in the tests.
-                 * So, we work around it by assuming an array is, in fact, a
-                 * `FlatConfigArray` if it has a `getConfig()` method.
-                 */
-                let configArray = config;
-
-                if (!Array.isArray(config) || typeof config.getConfig !== "function") {
-                    configArray = new FlatConfigArray(config, { basePath: cwd });
-                    configArray.normalizeSync();
-                }
+        const configToUse = config ?? {};
 
-                return this._distinguishSuppressedMessages(this._verifyWithFlatConfigArray(textOrSourceCode, configArray, options, true));
-            }
+        if (configType !== "eslintrc") {
+
+            /*
+             * Because of how Webpack packages up the files, we can't
+             * compare directly to `FlatConfigArray` using `instanceof`
+             * because it's not the same `FlatConfigArray` as in the tests.
+             * So, we work around it by assuming an array is, in fact, a
+             * `FlatConfigArray` if it has a `getConfig()` method.
+             */
+            let configArray = configToUse;
 
-            if (typeof config.extractConfig === "function") {
-                return this._distinguishSuppressedMessages(this._verifyWithConfigArray(textOrSourceCode, config, options));
+            if (!Array.isArray(configToUse) || typeof configToUse.getConfig !== "function") {
+                configArray = new FlatConfigArray(configToUse, { basePath: cwd });
+                configArray.normalizeSync();
             }
+
+            return this._distinguishSuppressedMessages(this._verifyWithFlatConfigArray(textOrSourceCode, configArray, options, true));
+        }
+
+        if (typeof configToUse.extractConfig === "function") {
+            return this._distinguishSuppressedMessages(this._verifyWithConfigArray(textOrSourceCode, configToUse, options));
         }
 
         /*
@@ -1403,9 +1403,9 @@ class Linter {
          * So we cannot apply multiple processors.
          */
         if (options.preprocess || options.postprocess) {
-            return this._distinguishSuppressedMessages(this._verifyWithProcessor(textOrSourceCode, config, options));
+            return this._distinguishSuppressedMessages(this._verifyWithProcessor(textOrSourceCode, configToUse, options));
         }
-        return this._distinguishSuppressedMessages(this._verifyWithoutProcessors(textOrSourceCode, config, options));
+        return this._distinguishSuppressedMessages(this._verifyWithoutProcessors(textOrSourceCode, configToUse, options));
     }
 
     /**

lib/rule-tester/rule-tester.js

@@ -426,7 +426,7 @@ class RuleTester {
          * @type {Object}
          */
         this.rules = {};
-        this.linter = new Linter();
+        this.linter = new Linter({ configType: "eslintrc" });
     }
 
     /**

tests/lib/linter/code-path-analysis/code-path-analyzer.js

@@ -31,7 +31,7 @@ const STANDARD_ESQUERY_OPTION = { visitorKeys: vk.KEYS, fallback: Traverser.getK
 
 const expectedPattern = /\/\*expected\s+((?:.|[\r\n])+?)\s*\*\//gu;
 const lineEndingPattern = /\r?\n/gu;
-const linter = new Linter();
+const linter = new Linter({ configType: "eslintrc" });
 
 /**
  * Extracts the content of `/*expected` comments from a given source code.

tests/lib/linter/code-path-analysis/code-path.js

@@ -11,7 +11,7 @@
 
 const assert = require("assert"),
     { Linter } = require("../../../../lib/linter");
-const linter = new Linter();
+const linter = new Linter({ configType: "eslintrc" });
 
 //------------------------------------------------------------------------------
 // Helpers

tests/lib/linter/linter.js

@@ -59,7 +59,7 @@ describe("Linter", () => {
     let linter;
 
     beforeEach(() => {
-        linter = new Linter();
+        linter = new Linter({ configType: "eslintrc" });
     });
 
     afterEach(() => {
@@ -1397,7 +1397,7 @@ describe("Linter", () => {
 
     describe("when evaluating code with invalid comments to enable rules", () => {
         it("should report a violation when the config is not a valid rule configuration", () => {
-            const messages = linter.verify("/*eslint no-alert:true*/ alert('test');", {});
+            const messages = linter.verify("/*eslint no-alert:true*/ alert('test');");
             const suppressedMessages = linter.getSuppressedMessages();
 
             assert.deepStrictEqual(
@@ -1420,7 +1420,7 @@ describe("Linter", () => {
         });
 
         it("should report a violation when the config violates a rule's schema", () => {
-            const messages = linter.verify("/* eslint no-alert: [error, {nonExistentPropertyName: true}]*/", {});
+            const messages = linter.verify("/* eslint no-alert: [error, {nonExistentPropertyName: true}]*/");
             const suppressedMessages = linter.getSuppressedMessages();
 
             assert.deepStrictEqual(
@@ -3509,7 +3509,7 @@ var a = "test2";
 
         it("should get cwd correctly in the context", () => {
             const cwd = "cwd";
-            const linterWithOption = new Linter({ cwd });
+            const linterWithOption = new Linter({ cwd, configType: "eslintrc" });
             let spy;
 
             linterWithOption.defineRule("checker", {
@@ -3528,7 +3528,7 @@ var a = "test2";
 
         it("should assign process.cwd() to it if cwd is undefined", () => {
             let spy;
-            const linterWithOption = new Linter({ });
+            const linterWithOption = new Linter({ configType: "eslintrc" });
 
             linterWithOption.defineRule("checker", {
                 create(context) {
@@ -6573,8 +6573,8 @@ var a = "test2";
         let linter2 = null;
 
         beforeEach(() => {
-            linter1 = new Linter();
-            linter2 = new Linter();
+            linter1 = new Linter({ configType: "eslintrc" });
+            linter2 = new Linter({ configType: "eslintrc" });
         });
 
         describe("rules", () => {
@@ -10320,7 +10320,7 @@ describe("Linter with FlatConfigArray", () => {
 
                 describe("when evaluating code with invalid comments to enable rules", () => {
                     it("should report a violation when the config is not a valid rule configuration", () => {
-                        const messages = linter.verify("/*eslint no-alert:true*/ alert('test');", {});
+                        const messages = linter.verify("/*eslint no-alert:true*/ alert('test');");
                         const suppressedMessages = linter.getSuppressedMessages();
 
                         assert.deepStrictEqual(
@@ -10343,7 +10343,7 @@ describe("Linter with FlatConfigArray", () => {
                     });
 
                     it("should report a violation when a rule is configured using a string severity that contains uppercase letters", () => {
-                        const messages = linter.verify("/*eslint no-alert: \"Error\"*/ alert('test');", {});
+                        const messages = linter.verify("/*eslint no-alert: \"Error\"*/ alert('test');");
                         const suppressedMessages = linter.getSuppressedMessages();
 
                         assert.deepStrictEqual(
@@ -10366,7 +10366,7 @@ describe("Linter with FlatConfigArray", () => {
                     });
 
                     it("should report a violation when the config violates a rule's schema", () => {
-                        const messages = linter.verify("/* eslint no-alert: [error, {nonExistentPropertyName: true}]*/", {});
+                        const messages = linter.verify("/* eslint no-alert: [error, {nonExistentPropertyName: true}]*/");
                         const suppressedMessages = linter.getSuppressedMessages();
 
                         assert.deepStrictEqual(
@@ -10395,7 +10395,7 @@ describe("Linter with FlatConfigArray", () => {
                             "foo(); // <-- expected no-undef error here"
                         ].join("\n");
 
-                        const messages = linter.verify(code, {});
+                        const messages = linter.verify(code);
                         const suppressedMessages = linter.getSuppressedMessages();
 
                         // different engines have different JSON parsing error messages
@@ -14508,7 +14508,7 @@ var a = "test2";
                 const code = BROKEN_TEST_CODE;
 
                 it("should report a violation with a useful parse error prefix", () => {
-                    const messages = linter.verify(code, {});
+                    const messages = linter.verify(code);
                     const suppressedMessages = linter.getSuppressedMessages();
 
                     assert.strictEqual(messages.length, 1);
@@ -14554,6 +14554,21 @@ var a = "test2";
             });
 
         });
+
+        it("should default to flat config mode when a config isn't passed", () => {
+
+            // eslint-env should not be honored
+            const messages = linter.verify("/*eslint no-undef:error*//*eslint-env browser*/\nwindow;");
+            const suppressedMessages = linter.getSuppressedMessages();
+
+            assert.strictEqual(messages.length, 1);
+            assert.strictEqual(messages[0].ruleId, "no-undef");
+            assert.strictEqual(messages[0].severity, 2);
+            assert.strictEqual(messages[0].line, 2);
+            assert.strictEqual(messages[0].column, 1);
+
+            assert.strictEqual(suppressedMessages.length, 0);
+        });
     });
 
     describe("getSourceCode()", () => {
@@ -14858,32 +14873,6 @@ var a = "test2";
         });
     });
 
-    describe("Mutability", () => {
-        let linter1 = null;
-        let linter2 = null;
-
-        beforeEach(() => {
-            linter1 = new Linter();
-            linter2 = new Linter();
-        });
-
-        describe("rules", () => {
-            it("with no changes, same rules are loaded", () => {
-                assert.sameDeepMembers(Array.from(linter1.getRules().keys()), Array.from(linter2.getRules().keys()));
-            });
-
-            it("loading rule in one doesn't change the other", () => {
-                linter1.defineRule("mock-rule", {
-                    create: () => ({})
-                });
-
-                assert.isTrue(linter1.getRules().has("mock-rule"), "mock rule is present");
-                assert.isFalse(linter2.getRules().has("mock-rule"), "mock rule is not present");
-            });
-        });
-    });
-
-
     describe("processors", () => {
         let receivedFilenames = [];
         let receivedPhysicalFilenames = [];
@@ -15465,7 +15454,7 @@ var a = "test2";
         });
 
         it("should not crash when invalid parentheses syntax is encountered", () => {
-            linter.verify("left = (aSize.width/2) - ()", {});
+            linter.verify("left = (aSize.width/2) - ()");
         });
 
         it("should not crash when let is used inside of switch case", () => {

tests/lib/linter/rules.js

@@ -58,30 +58,19 @@ describe("rules", () => {
 
             const linter = new Linter();
 
-            const problems = linter.verify("foo", { rules: { "test-rule": "error" } });
-
-            assert.lengthOf(problems, 1);
-            assert.strictEqual(problems[0].message, "Definition for rule 'test-rule' was not found.");
-            assert.strictEqual(problems[0].line, 1);
-            assert.strictEqual(problems[0].column, 1);
-            assert.strictEqual(problems[0].endLine, 1);
-            assert.strictEqual(problems[0].endColumn, 2);
+            assert.throws(() => {
+                linter.verify("foo", { rules: { "test-rule": "error" } });
+            }, TypeError, "Could not find \"test-rule\" in plugin \"@\".");
+
         });
 
 
         it("should report a linting error that lists replacements if a rule is known to have been replaced", () => {
             const linter = new Linter();
-            const problems = linter.verify("foo", { rules: { "no-arrow-condition": "error" } });
-
-            assert.lengthOf(problems, 1);
-            assert.strictEqual(
-                problems[0].message,
-                "Rule 'no-arrow-condition' was removed and replaced by: no-confusing-arrow, no-constant-condition"
-            );
-            assert.strictEqual(problems[0].line, 1);
-            assert.strictEqual(problems[0].column, 1);
-            assert.strictEqual(problems[0].endLine, 1);
-            assert.strictEqual(problems[0].endColumn, 2);
+
+            assert.throws(() => {
+                linter.verify("foo", { rules: { "no-arrow-condition": "error" } });
+            }, TypeError, "Key \"rules\": Key \"no-arrow-condition\": Rule \"no-arrow-condition\" was removed and replaced by \"no-confusing-arrow,no-constant-condition\".");
         });
     });
 

tests/lib/rules/utils/ast-utils.js

@@ -27,7 +27,7 @@ const ESPREE_CONFIG = {
     range: true,
     loc: true
 };
-const linter = new Linter();
+const linter = new Linter({ configType: "eslintrc" });
 
 describe("ast-utils", () => {
     let callCounts;

tests/lib/shared/config-validator.js

@@ -30,7 +30,7 @@ const assert = require("chai").assert,
 // Helpers
 //------------------------------------------------------------------------------
 
-const linter = new Linter();
+const linter = new Linter({ configType: "eslintrc" });
 
 const mockRule = {
     meta: {

tests/lib/source-code/source-code.js

@@ -29,7 +29,7 @@ const DEFAULT_CONFIG = {
     range: true,
     loc: true
 };
-const linter = new Linter();
+const linter = new Linter({ configType: "eslintrc" });
 const flatLinter = new Linter({ configType: "flat" });
 const AST = espree.parse("let foo = bar;", DEFAULT_CONFIG),
     TEST_CODE = "var answer = 6 * 7;",

tests/tools/eslint-fuzzer.js

@@ -23,7 +23,7 @@ describe("eslint-fuzzer", function() {
      */
     this.timeout(15000); // eslint-disable-line no-invalid-this -- Mocha timeout
 
-    const linter = new eslint.Linter();
+    const linter = new eslint.Linter({ configType: "eslintrc" });
     const coreRules = linter.getRules();
     const fixableRuleNames = Array.from(coreRules)
         .filter(rulePair => rulePair[1].meta && rulePair[1].meta.fixable)

tools/fuzzer-runner.js

@@ -12,7 +12,7 @@
 const ProgressBar = require("progress");
 const fuzz = require("./eslint-fuzzer");
 const eslint = require("..");
-const linter = new eslint.Linter();
+const linter = new eslint.Linter({ configType: "eslintrc" });
 
 //------------------------------------------------------------------------------
 // Helpers