Fix: clone config before validating (fixes #12592)

lib/cli-engine/config-array-factory.js

@@ -623,8 +623,11 @@ class ConfigArrayFactory {
      * @private
      */
     _normalizeConfigData(configData, ctx) {
+
         validateConfigSchema(configData, ctx.name || ctx.filePath);
-        return this._normalizeObjectConfigData(configData, ctx);
+        const clonedConfig = JSON.parse(JSON.stringify(configData));
+
+        return this._normalizeObjectConfigData(clonedConfig, ctx);
     }
 
     /**

tests/fixtures/config-file/cloned-config/eslintConfig.js

@@ -0,0 +1,4 @@
+let errorConfig = ["error", {}];
+module.exports = {
+    rules: { camelcase: errorConfig, "default-case": errorConfig }
+};

tests/fixtures/config-file/cloned-config/index.js

@@ -0,0 +1 @@
+var someValue  = "bar";

tests/fixtures/config-file/cloned-config/inlineText.js

@@ -0,0 +1,3 @@
+/*eslint default-case: ["error", {}]*/
+/*eslint camelcase: ["error", {}]*/
+var someValue  = "bar";

tests/lib/cli.js

@@ -187,6 +187,7 @@ describe("cli", () => {
         });
     });
 
+
     describe("when given a config with environment set to Node.js", () => {
         it("should execute without any errors", async () => {
             const configPath = getFixturePath("configurations", "env-node.json");
@@ -1160,4 +1161,29 @@ describe("cli", () => {
         });
     });
 
+    describe("testing the cloned config", () => {
+        describe("config file and input file", () => {
+            it("should not modify original configuration object", async () => {
+                const configPath = getFixturePath("config-file", "cloned-config", "eslintConfig.js");
+                const filePath = getFixturePath("config-file", "cloned-config", "index.js");
+                const args = `--config ${configPath} ${filePath}`;
+
+                const exit = await cli.execute(args);
+
+                assert.strictEqual(exit, 0);
+            });
+        });
+
+        describe("inline config and input file", () => {
+            it("should not modify original configuration object", async () => {
+                const filePath = getFixturePath("config-file", "cloned-config", "inlineText.js");
+                const args = `${filePath}`;
+
+                const exit = await cli.execute(args);
+
+                assert.strictEqual(exit, 0);
+            });
+        });
+    });
+
 });