fix: Ensure shared references in rule configs are separated.

lib/config/flat-config-schema.js

@@ -5,6 +5,16 @@
 
 "use strict";
 
+//-----------------------------------------------------------------------------
+// Requirements
+//-----------------------------------------------------------------------------
+
+/*
+ * Note: This can be removed in ESLint v9 because structuredClone is available globally
+ * starting in Node.js v17.
+ */
+const structuredClone = require("@ungap/structured-clone").default;
+
 //-----------------------------------------------------------------------------
 // Type Definitions
 //-----------------------------------------------------------------------------
@@ -119,7 +129,7 @@ function normalizeRuleOptions(ruleOptions) {
         : [ruleOptions];
 
     finalOptions[0] = ruleSeverities.get(finalOptions[0]);
-    return finalOptions;
+    return finalOptions.map(value => structuredClone(value));
 }
 
 //-----------------------------------------------------------------------------
@@ -378,48 +388,57 @@ const rulesSchema = {
             ...second
         };
 
-        for (const ruleId of Object.keys(result)) {
-
-            // avoid hairy edge case
-            if (ruleId === "__proto__") {
-
-                /* eslint-disable-next-line no-proto -- Though deprecated, may still be present */
-                delete result.__proto__;
-                continue;
-            }
-
-            result[ruleId] = normalizeRuleOptions(result[ruleId]);
-
-            /*
-             * If either rule config is missing, then the correct
-             * config is already present and we just need to normalize
-             * the severity.
-             */
-            if (!(ruleId in first) || !(ruleId in second)) {
-                continue;
-            }
 
-            const firstRuleOptions = normalizeRuleOptions(first[ruleId]);
-            const secondRuleOptions = normalizeRuleOptions(second[ruleId]);
+        for (const ruleId of Object.keys(result)) {
 
-            /*
-             * If the second rule config only has a severity (length of 1),
-             * then use that severity and keep the rest of the options from
-             * the first rule config.
-             */
-            if (secondRuleOptions.length === 1) {
-                result[ruleId] = [secondRuleOptions[0], ...firstRuleOptions.slice(1)];
-                continue;
+            try {
+
+                // avoid hairy edge case
+                if (ruleId === "__proto__") {
+
+                    /* eslint-disable-next-line no-proto -- Though deprecated, may still be present */
+                    delete result.__proto__;
+                    continue;
+                }
+
+                result[ruleId] = normalizeRuleOptions(result[ruleId]);
+
+                /*
+                 * If either rule config is missing, then the correct
+                 * config is already present and we just need to normalize
+                 * the severity.
+                 */
+                if (!(ruleId in first) || !(ruleId in second)) {
+                    continue;
+                }
+
+                const firstRuleOptions = normalizeRuleOptions(first[ruleId]);
+                const secondRuleOptions = normalizeRuleOptions(second[ruleId]);
+
+                /*
+                 * If the second rule config only has a severity (length of 1),
+                 * then use that severity and keep the rest of the options from
+                 * the first rule config.
+                 */
+                if (secondRuleOptions.length === 1) {
+                    result[ruleId] = [secondRuleOptions[0], ...firstRuleOptions.slice(1)];
+                    continue;
+                }
+
+                /*
+                 * In any other situation, then the second rule config takes
+                 * precedence. That means the value at `result[ruleId]` is
+                 * already correct and no further work is necessary.
+                 */
+            } catch (ex) {
+                throw new Error(`Key "${ruleId}": ${ex.message}`, { cause: ex });
             }
 
-            /*
-             * In any other situation, then the second rule config takes
-             * precedence. That means the value at `result[ruleId]` is
-             * already correct and no further work is necessary.
-             */
         }
 
         return result;
+
+
     },
 
     validate(value) {

package.json

@@ -64,9 +64,10 @@
     "@eslint-community/regexpp": "^4.6.1",
     "@eslint/eslintrc": "^2.1.2",
     "@eslint/js": "8.51.0",
-    "@humanwhocodes/config-array": "^0.11.11",
+    "@humanwhocodes/config-array": "^0.11.12",
     "@humanwhocodes/module-importer": "^1.0.1",
     "@nodelib/fs.walk": "^1.2.8",
+    "@ungap/structured-clone": "^1.2.0",
     "ajv": "^6.12.4",
     "chalk": "^4.0.0",
     "cross-spawn": "^7.0.2",

tests/lib/config/flat-config-array.js

@@ -1987,4 +1987,65 @@ describe("FlatConfigArray", () => {
         });
 
     });
+
+    // https://github.com/eslint/eslint/issues/12592
+    describe("Shared references between rule configs", () => {
+
+        it("shared rule config should not cause a rule validation error", () => {
+
+            const ruleConfig = ["error", {}];
+
+            const configs = new FlatConfigArray([{
+                rules: {
+                    camelcase: ruleConfig,
+                    "default-case": ruleConfig
+                }
+            }]);
+
+            configs.normalizeSync();
+
+            const config = configs.getConfig("foo.js");
+
+            assert.deepStrictEqual(config.rules, {
+                camelcase: [2, {
+                    ignoreDestructuring: false,
+                    ignoreGlobals: false,
+                    ignoreImports: false
+                }],
+                "default-case": [2, {}]
+            });
+
+        });
+
+
+        it("should throw rule validation error for camelcase", async () => {
+
+            const ruleConfig = ["error", {}];
+
+            const configs = new FlatConfigArray([{
+                rules: {
+                    camelcase: ruleConfig,
+                    "default-case": ruleConfig,
+
+                    /* eslint-disable-next-line no-dupe-keys -- needed for testing */
+                    camelcase: [
+                        "error",
+                        {
+                            ignoreDestructuring: Date
+                        }
+
+                    ]
+                }
+            }]);
+
+            configs.normalizeSync();
+
+            // exact error may differ based on structuredClone implementation so just test prefix
+            assert.throws(() => {
+                configs.getConfig("foo.js");
+            }, /Key "rules": Key "camelcase":/u);
+
+        });
+
+    });
 });