fix(purity): report Date constructor arguments, closes #1759

plugins/eslint-plugin-react-x/src/rules/purity/CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to the `react-x/purity` rule will be documented in this file
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Fixed
+
+- Treat `new Date(...)` calls with arguments as impure during render to match the React Compiler spec. Closes #1759.
+
 ## [5.5.3-beta.1] - 2026-04-27
 
 ### Added

plugins/eslint-plugin-react-x/src/rules/purity/purity.spec.diff.md

@@ -40,9 +40,9 @@ Detection uses only `IMPURE_FUNCS` and `IMPURE_CTORS`. Although `lib.ts` also ex
 - **ESLint**: only names present in `IMPURE_FUNCS` or `IMPURE_CTORS` are candidates.
 - **ESLint aliases**: `resolveBuiltinObjectName` follows simple variable-initializer chains to a global root, such as `const M = Math` and `const D = Date`.
 - **ESLint shadowing**: parameters, imports, function declarations, and other local definitions do not resolve as built-ins; implicit or unresolved globals do.
-- **ESLint constructors**: constructors in `IMPURE_CTORS` are reported, except `new Date(arg)` is allowed when at least one argument is present; zero-argument `new Date()` is reported.
+- **ESLint constructors**: constructors in `IMPURE_CTORS` are reported, including `new Date(...)` with or without arguments.
 
-**Verdict**: Alias, shadowing, and the `new Date(arg)` exception are explicit ESLint behaviors. The cited React fixture does not establish corresponding upstream behavior.
+**Verdict**: Alias and shadowing are explicit ESLint behaviors. `new Date(...)` constructor calls are reported like the other constructors in `IMPURE_CTORS`.
 
 ## 3. Reporting
 
@@ -69,7 +69,7 @@ There is no current upstream dual-location diagnostic to reproduce. The React ex
 
 - React's active branch, option gate, signature check, `Purity` category, reason, and single call location.
 - The standalone React validator is present but not connected to `Pipeline.ts`.
-- ESLint's exclusive use of `IMPURE_FUNCS` / `IMPURE_CTORS`, component-hook ownership check, alias resolution, shadowing handling, and `new Date(arg)` exception.
+- ESLint's exclusive use of `IMPURE_FUNCS` / `IMPURE_CTORS`, component-hook ownership check, alias resolution, shadowing handling, and Date constructor handling.
 
 ### Fixture-verified
 

plugins/eslint-plugin-react-x/src/rules/purity/purity.spec.ts

@@ -301,6 +301,41 @@ ruleTester.run(RULE_NAME, rule, {
       `,
       errors: [{ messageId: "default" }],
     },
+    {
+      code: tsx`
+        function Component() {
+          const date = new Date("2024-01-01");
+          return <div>{date.toISOString()}</div>;
+        }
+      `,
+      errors: [{ messageId: "default" }],
+    },
+    {
+      code: tsx`
+        function Component({ timestamp }: { timestamp: number }) {
+          const date = new Date(timestamp);
+          return <div>{date.toISOString()}</div>;
+        }
+      `,
+      errors: [{ messageId: "default" }],
+    },
+    {
+      code: tsx`
+        function Component({ year, month, day }: { year: number; month: number; day: number }) {
+          const date = new Date(year, month, day);
+          return <div>{date.toISOString()}</div>;
+        }
+      `,
+      errors: [{ messageId: "default" }],
+    },
+    {
+      code: tsx`
+        function Component({ myDate }: { myDate: string }) {
+          return new Date(myDate) < new Date("2020-01-01") ? <span>one</span> : <span>two</span>;
+        }
+      `,
+      errors: [{ messageId: "default" }, { messageId: "default" }],
+    },
     {
       code: tsx`
         function Component() {
@@ -528,6 +563,15 @@ ruleTester.run(RULE_NAME, rule, {
       `,
       errors: [{ messageId: "default" }],
     },
+    {
+      code: tsx`
+        function useFormattedDate(input: string) {
+          const date = new Date(input);
+          return date.toLocaleDateString();
+        }
+      `,
+      errors: [{ messageId: "default" }],
+    },
     {
       code: tsx`
         function useStorage() {
@@ -1423,48 +1467,6 @@ ruleTester.run(RULE_NAME, rule, {
       `,
     },
     // -------------------------------------------------------------------------
-    // new Date(arg) with arguments is pure (deterministic)
-    // -------------------------------------------------------------------------
-    {
-      code: tsx`
-        function Component({ myDate }: { myDate: string }) {
-          return new Date(myDate) < new Date("2020-01-01") ? <span>one</span> : <span>two</span>;
-        }
-      `,
-    },
-    {
-      code: tsx`
-        function Component() {
-          const date = new Date("2024-01-01");
-          return <div>{date.toISOString()}</div>;
-        }
-      `,
-    },
-    {
-      code: tsx`
-        function Component({ timestamp }: { timestamp: number }) {
-          const date = new Date(timestamp);
-          return <div>{date.toISOString()}</div>;
-        }
-      `,
-    },
-    {
-      code: tsx`
-        function useFormattedDate(input: string) {
-          const date = new Date(input);
-          return date.toLocaleDateString();
-        }
-      `,
-    },
-    {
-      code: tsx`
-        function Component({ year, month, day }: { year: number; month: number; day: number }) {
-          const date = new Date(year, month, day);
-          return <div>{date.toISOString()}</div>;
-        }
-      `,
-    },
-    // -------------------------------------------------------------------------
     // Local shadowing of builtins (should NOT be flagged)
     // -------------------------------------------------------------------------
     {

plugins/eslint-plugin-react-x/src/rules/purity/purity.ts

@@ -77,9 +77,6 @@ export function create(context: RuleContext<MessageID, []>): RuleListener {
         const builtinName = resolveBuiltinObjectName(context, expr);
         if (builtinName == null) return;
         if (!IMPURE_CTORS.has(builtinName)) return;
-        // `new Date(arg)` with arguments is pure (deterministic),
-        // only `new Date()` without arguments is impure (depends on current time).
-        if (builtinName === "Date" && node.arguments.length > 0) return;
         const func = Traverse.findParent(node, Check.isFunction);
         if (func == null) return;
         nEntries.push({ func, node });