From 989a414a1a1509c64a08a503fcf135aa7b452e6a Mon Sep 17 00:00:00 2001
From: Lauren Tan <poteto@users.noreply.github.com>
Date: Wed, 8 Oct 2025 12:46:11 -0700
Subject: [PATCH] [compiler] Add VoidUseMemo rule to RecommendedLatest

Adds a new error category VoidUseMemo which is only enabled in the RecommendedLatest preset for now.
---
 .../src/CompilerError.ts                        | 17 ++++++++++++++++-
 .../src/Inference/DropManualMemoization.ts      |  2 +-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/compiler/packages/babel-plugin-react-compiler/src/CompilerError.ts b/compiler/packages/babel-plugin-react-compiler/src/CompilerError.ts
index 0db911dbe56c8..1c077edd8d8a5 100644
--- a/compiler/packages/babel-plugin-react-compiler/src/CompilerError.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/CompilerError.ts
@@ -536,7 +536,8 @@ function printErrorSummary(category: ErrorCategory, message: string): string {
     case ErrorCategory.StaticComponents:
     case ErrorCategory.Suppression:
     case ErrorCategory.Syntax:
-    case ErrorCategory.UseMemo: {
+    case ErrorCategory.UseMemo:
+    case ErrorCategory.VoidUseMemo: {
       heading = 'Error';
       break;
     }
@@ -582,6 +583,10 @@ export enum ErrorCategory {
    * Checking for valid usage of manual memoization
    */
   UseMemo = 'UseMemo',
+  /**
+   * Checking that useMemos always return a value
+   */
+  VoidUseMemo = 'VoidUseMemo',
   /**
    * Checking for higher order functions acting as factories for components/hooks
    */
@@ -977,6 +982,16 @@ function getRuleForCategoryImpl(category: ErrorCategory): LintRule {
         preset: LintRulePreset.Recommended,
       };
     }
+    case ErrorCategory.VoidUseMemo: {
+      return {
+        category,
+        severity: ErrorSeverity.Error,
+        name: 'void-use-memo',
+        description:
+          'Validates that useMemos always return a value. See [`useMemo()` docs](https://react.dev/reference/react/useMemo) for more information.',
+        preset: LintRulePreset.RecommendedLatest,
+      };
+    }
     case ErrorCategory.IncompatibleLibrary: {
       return {
         category,
diff --git a/compiler/packages/babel-plugin-react-compiler/src/Inference/DropManualMemoization.ts b/compiler/packages/babel-plugin-react-compiler/src/Inference/DropManualMemoization.ts
index 3eaeb5e4aa037..f86747618dd59 100644
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/DropManualMemoization.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/DropManualMemoization.ts
@@ -454,7 +454,7 @@ export function dropManualMemoization(
               if (!hasNonVoidReturn(funcToCheck.loweredFunc.func)) {
                 errors.pushDiagnostic(
                   CompilerDiagnostic.create({
-                    category: ErrorCategory.UseMemo,
+                    category: ErrorCategory.VoidUseMemo,
                     reason: 'useMemo() callbacks must return a value',
                     description: `This ${
                       manualMemo.loadInstr.value.kind === 'PropertyLoad'