Enforce deps array in useMemo and useCallback (#15025)

gaearon · web-flow · commit 5d49dafac807 · 2019-03-06T18:17:54.000Z
diff --git a/packages/eslint-plugin-react-hooks/__tests__/ESLintRuleExhaustiveDeps-test.js b/packages/eslint-plugin-react-hooks/__tests__/ESLintRuleExhaustiveDeps-test.js
@@ -178,6 +178,16 @@ const tests = {
         }
       `,
     },
+    {
+      // Valid because they have meaning without deps.
+      code: `
+        function MyComponent(props) {
+          useEffect(() => {});
+          useLayoutEffect(() => {});
+          useImperativeHandle(props.innerRef, () => {});
+        }
+      `,
+    },
     {
       code: `
         function MyComponent(props) {
@@ -924,6 +934,26 @@ const tests = {
           'Either include it or remove the dependency array.',
       ],
     },
+    {
+      // Invalid because they don't have a meaning without deps.
+      code: `
+        function MyComponent(props) {
+          const value = useMemo(() => { return 2*2; });
+          const fn = useCallback(() => { alert('foo'); });
+        }
+      `,
+      // We don't know what you meant.
+      output: `
+        function MyComponent(props) {
+          const value = useMemo(() => { return 2*2; });
+          const fn = useCallback(() => { alert('foo'); });
+        }
+      `,
+      errors: [
+        "React Hook useMemo doesn't serve any purpose without a dependency array as a second argument.",
+        "React Hook useCallback doesn't serve any purpose without a dependency array as a second argument.",
+      ],
+    },
     {
       // Regression test
       code: `
diff --git a/packages/eslint-plugin-react-hooks/src/ExhaustiveDeps.js b/packages/eslint-plugin-react-hooks/src/ExhaustiveDeps.js
@@ -87,6 +87,18 @@ export default {
       const depsIndex = callbackIndex + 1;
       const declaredDependenciesNode = node.parent.arguments[depsIndex];
       if (!declaredDependenciesNode) {
+        // These are only used for optimization.
+        if (
+          reactiveHookName === 'useMemo' ||
+          reactiveHookName === 'useCallback'
+        ) {
+          context.report({
+            node: node,
+            message:
+              `React Hook ${reactiveHookName} doesn't serve any purpose ` +
+              `without a dependency array as a second argument.`,
+          });
+        }
         return;
       }
 
