prefer-number-isnan: treat ESM import bindings as local shadows (#43500)

Author: Copilot

eslint-factory/src/rules/prefer-number-isnan.test.ts

@@ -34,9 +34,13 @@ describe("prefer-number-isnan", () => {
       valid: [
         `function isNaN(value) { return false; } isNaN(value);`,
         `const isNaN = Number.isNaN; isNaN(value);`,
+        `import { isNaN } from "lodash"; isNaN(value);`,
         `const globalThis = { isNaN(value) { return value; } }; globalThis.isNaN(value);`,
         `const window = { isNaN(value) { return value; } }; window["isNaN"](value);`,
         `const global = { isNaN(value) { return value; } }; global.isNaN(value);`,
+        `import { globalThis } from "./global-shim"; globalThis.isNaN(value);`,
+        `import { window } from "./browser-shim"; window.isNaN(value);`,
+        `import { global } from "./server-shim"; global["isNaN"](value);`,
         // Dynamic computed access — identifier property reference, not string literal "isNaN"
         `globalThis[isNaN](value);`,
       ],
@@ -99,4 +103,20 @@ describe("prefer-number-isnan", () => {
       ],
     });
   });
+
+  it("invalid: global isNaN() is still flagged in ESM mode without a shadow", () => {
+    esmRuleTester.run("prefer-number-isnan", preferNumberIsNanRule, {
+      valid: [],
+      invalid: [
+        {
+          code: `isNaN(value);`,
+          errors: [{ messageId: "preferNumberIsNaN", suggestions: [{ messageId: "replaceWithNumberIsNaN", output: `Number.isNaN(value);` }] }],
+        },
+        {
+          code: `window.isNaN(value);`,
+          errors: [{ messageId: "preferNumberIsNaN", suggestions: [{ messageId: "replaceWithNumberIsNaN", output: `Number.isNaN(value);` }] }],
+        },
+      ],
+    });
+  });
 });

eslint-factory/src/rules/prefer-number-isnan.ts

@@ -34,7 +34,8 @@ export const preferNumberIsNanRule = createRule({
       while (scope) {
         const variable = scope.set.get(name);
 
-        if (variable?.defs.some(d => d.type !== "ImportBinding")) {
+        // Any local definition shadows the global (including ESM ImportBinding).
+        if (variable && variable.defs.length > 0) {
           return true;
         }