[compiler] Cleanup and enable validateNoVoidUseMemo (#34882)

This is a great validation, so let's enable by default. Changes:
* Move the validation logic into ValidateUseMemo alongside the new check
that the useMemo result is used
* Update the lint description
* Make the void memo errors lint-only, they don't require us to skip
compilation (as evidenced by the fact that we've had this validation
off)

---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/facebook/react/pull/34882).
* #34855
* __->__ #34882

DiffTrain build for [1324e1b](1324e1b)

Author: josephsavona

compiled/eslint-plugin-react-hooks/index.js

@@ -18309,7 +18309,7 @@ function getRuleForCategoryImpl(category) {
                 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.',
+                description: 'Validates that useMemos always return a value and that the result of the useMemo is used by the component/hook. See [`useMemo()` docs](https://react.dev/reference/react/useMemo) for more information.',
                 preset: LintRulePreset.RecommendedLatest,
             };
         }
@@ -32187,7 +32187,7 @@ const EnvironmentConfigSchema = v4.z.object({
     enableTreatRefLikeIdentifiersAsRefs: v4.z.boolean().default(true),
     enableTreatSetIdentifiersAsStateSetters: v4.z.boolean().default(false),
     lowerContextAccess: ExternalFunctionSchema.nullable().default(null),
-    validateNoVoidUseMemo: v4.z.boolean().default(false),
+    validateNoVoidUseMemo: v4.z.boolean().default(true),
     validateNoDynamicallyCreatedComponentsOrHooks: v4.z.boolean().default(false),
     enableAllowSetStateFromRefsInEffects: v4.z.boolean().default(true),
 });
@@ -44571,7 +44571,6 @@ function extractManualMemoizationArgs(instr, kind, sidemap, errors) {
     };
 }
 function dropManualMemoization(func) {
-    var _a;
     const errors = new CompilerError();
     const isValidationEnabled = func.env.config.validatePreserveExistingMemoizationGuarantees ||
         func.env.config.validateNoSetStateInRender ||
@@ -44601,26 +44600,6 @@ function dropManualMemoization(func) {
                     if (fnPlace == null) {
                         continue;
                     }
-                    if (func.env.config.validateNoVoidUseMemo &&
-                        manualMemo.kind === 'useMemo') {
-                        const funcToCheck = (_a = sidemap.functions.get(fnPlace.identifier.id)) === null || _a === void 0 ? void 0 : _a.value;
-                        if (funcToCheck !== undefined && funcToCheck.loweredFunc.func) {
-                            if (!hasNonVoidReturn(funcToCheck.loweredFunc.func)) {
-                                errors.pushDiagnostic(CompilerDiagnostic.create({
-                                    category: ErrorCategory.VoidUseMemo,
-                                    reason: 'useMemo() callbacks must return a value',
-                                    description: `This ${manualMemo.loadInstr.value.kind === 'PropertyLoad'
-                                        ? 'React.useMemo()'
-                                        : 'useMemo()'} callback doesn't return a value. useMemo() is for computing and caching values, not for arbitrary side effects`,
-                                    suggestions: null,
-                                }).withDetails({
-                                    kind: 'error',
-                                    loc: instr.value.loc,
-                                    message: 'useMemo() callbacks must return a value',
-                                }));
-                            }
-                        }
-                    }
                     instr.value = getManualMemoizationReplacement(fnPlace, instr.value.loc, manualMemo.kind);
                     if (isValidationEnabled) {
                         if (!sidemap.functions.has(fnPlace.identifier.id)) {
@@ -44732,17 +44711,6 @@ function findOptionalPlaces(fn) {
     }
     return optionals;
 }
-function hasNonVoidReturn(func) {
-    for (const [, block] of func.body.blocks) {
-        if (block.terminal.kind === 'return') {
-            if (block.terminal.returnVariant === 'Explicit' ||
-                block.terminal.returnVariant === 'Implicit') {
-                return true;
-            }
-        }
-    }
-    return false;
-}
 
 class StableSidemap {
     constructor(env) {
@@ -50225,6 +50193,7 @@ function isUnmemoized(operand, scopes) {
 
 function validateUseMemo(fn) {
     const errors = new CompilerError();
+    const voidMemoErrors = new CompilerError();
     const useMemos = new Set();
     const react = new Set();
     const functions = new Map();
@@ -50303,7 +50272,21 @@ function validateUseMemo(fn) {
                     }
                     validateNoContextVariableAssignment(body.loweredFunc.func, errors);
                     if (fn.env.config.validateNoVoidUseMemo) {
-                        unusedUseMemos.set(lvalue.identifier.id, callee.loc);
+                        if (!hasNonVoidReturn(body.loweredFunc.func)) {
+                            voidMemoErrors.pushDiagnostic(CompilerDiagnostic.create({
+                                category: ErrorCategory.VoidUseMemo,
+                                reason: 'useMemo() callbacks must return a value',
+                                description: `This useMemo() callback doesn't return a value. useMemo() is for computing and caching values, not for arbitrary side effects`,
+                                suggestions: null,
+                            }).withDetails({
+                                kind: 'error',
+                                loc: body.loc,
+                                message: 'useMemo() callbacks must return a value',
+                            }));
+                        }
+                        else {
+                            unusedUseMemos.set(lvalue.identifier.id, callee.loc);
+                        }
                     }
                     break;
                 }
@@ -50317,9 +50300,9 @@ function validateUseMemo(fn) {
     }
     if (unusedUseMemos.size !== 0) {
         for (const loc of unusedUseMemos.values()) {
-            errors.pushDiagnostic(CompilerDiagnostic.create({
+            voidMemoErrors.pushDiagnostic(CompilerDiagnostic.create({
                 category: ErrorCategory.VoidUseMemo,
-                reason: 'Unused useMemo()',
+                reason: 'useMemo() result is unused',
                 description: `This useMemo() value is unused. useMemo() is for computing and caching values, not for arbitrary side effects`,
                 suggestions: null,
             }).withDetails({
@@ -50329,6 +50312,7 @@ function validateUseMemo(fn) {
             }));
         }
     }
+    fn.env.logErrors(voidMemoErrors.asResult());
     return errors.asResult();
 }
 function validateNoContextVariableAssignment(fn, errors) {
@@ -50353,6 +50337,17 @@ function validateNoContextVariableAssignment(fn, errors) {
         }
     }
 }
+function hasNonVoidReturn(func) {
+    for (const [, block] of func.body.blocks) {
+        if (block.terminal.kind === 'return') {
+            if (block.terminal.returnVariant === 'Explicit' ||
+                block.terminal.returnVariant === 'Implicit') {
+                return true;
+            }
+        }
+    }
+    return false;
+}
 
 function validateLocalsNotReassignedAfterRender(fn) {
     const contextVariables = new Set();

compiled/facebook-www/REVISION

@@ -1 +1 @@
-7f5ea1bf67a1a920919ebe2ae6657bdebe505aa0
+1324e1bb1f867e8b2108ca52a1d4e2d4ef56d2d9

compiled/facebook-www/REVISION_TRANSFORMS

@@ -1 +1 @@
-7f5ea1bf67a1a920919ebe2ae6657bdebe505aa0
+1324e1bb1f867e8b2108ca52a1d4e2d4ef56d2d9

compiled/facebook-www/React-dev.classic.js

@@ -1478,7 +1478,7 @@ __DEV__ &&
     exports.useTransition = function () {
       return resolveDispatcher().useTransition();
     };
-    exports.version = "19.3.0-www-classic-7f5ea1bf-20251016";
+    exports.version = "19.3.0-www-classic-1324e1bb-20251016";
     "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
       "function" ===
         typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

compiled/facebook-www/React-dev.modern.js

@@ -1478,7 +1478,7 @@ __DEV__ &&
     exports.useTransition = function () {
       return resolveDispatcher().useTransition();
     };
-    exports.version = "19.3.0-www-modern-7f5ea1bf-20251016";
+    exports.version = "19.3.0-www-modern-1324e1bb-20251016";
     "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
       "function" ===
         typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

compiled/facebook-www/React-prod.classic.js

@@ -606,4 +606,4 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-classic-7f5ea1bf-20251016";
+exports.version = "19.3.0-www-classic-1324e1bb-20251016";

compiled/facebook-www/React-prod.modern.js

@@ -606,4 +606,4 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-modern-7f5ea1bf-20251016";
+exports.version = "19.3.0-www-modern-1324e1bb-20251016";

compiled/facebook-www/React-profiling.classic.js

@@ -610,7 +610,7 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-classic-7f5ea1bf-20251016";
+exports.version = "19.3.0-www-classic-1324e1bb-20251016";
 "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
   "function" ===
     typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

compiled/facebook-www/React-profiling.modern.js

@@ -610,7 +610,7 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-modern-7f5ea1bf-20251016";
+exports.version = "19.3.0-www-modern-1324e1bb-20251016";
 "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
   "function" ===
     typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

compiled/facebook-www/ReactART-dev.classic.js

@@ -20371,10 +20371,10 @@ __DEV__ &&
     (function () {
       var internals = {
         bundleType: 1,
-        version: "19.3.0-www-classic-7f5ea1bf-20251016",
+        version: "19.3.0-www-classic-1324e1bb-20251016",
         rendererPackageName: "react-art",
         currentDispatcherRef: ReactSharedInternals,
-        reconcilerVersion: "19.3.0-www-classic-7f5ea1bf-20251016"
+        reconcilerVersion: "19.3.0-www-classic-1324e1bb-20251016"
       };
       internals.overrideHookState = overrideHookState;
       internals.overrideHookStateDeletePath = overrideHookStateDeletePath;
@@ -20409,7 +20409,7 @@ __DEV__ &&
     exports.Shape = Shape;
     exports.Surface = Surface;
     exports.Text = Text;
-    exports.version = "19.3.0-www-classic-7f5ea1bf-20251016";
+    exports.version = "19.3.0-www-classic-1324e1bb-20251016";
     "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
       "function" ===
         typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&