[ESLint] Disallow hooks in async functions (facebook#27045)

Hooks cannot be called in async functions, on either the client or the
server. This mistake sometimes happens when using Server Components,
especially when refactoring a Server Component to a Client Component.

React logs a warning at runtime, but it's even better to catch this with
a lint rule since it will show immediate inline feedback in the editor.

I added this to the existing "Rules of Hooks" ESLint rule.

packages/eslint-plugin-react-hooks/__tests__/ESLintRulesOfHooks-test.js

@@ -1042,6 +1042,22 @@ const tests = {
       `,
       errors: [classError('useState')],
     },
+    {
+      code: normalizeIndent`
+        async function AsyncComponent() {
+          useState();
+        }
+      `,
+      errors: [asyncComponentHookError('useState')],
+    },
+    {
+      code: normalizeIndent`
+        async function useAsyncHook() {
+          useState();
+        }
+      `,
+      errors: [asyncComponentHookError('useState')],
+    },
   ],
 };
 
@@ -1300,6 +1316,14 @@ if (__EXPERIMENTAL__) {
       `,
       errors: [classError('use')],
     },
+    {
+      code: normalizeIndent`
+        async function AsyncComponent() {
+          use();
+        }
+      `,
+      errors: [asyncComponentHookError('use')],
+    },
   ];
 }
 
@@ -1368,6 +1392,12 @@ function useEffectEventError(fn) {
   };
 }
 
+function asyncComponentHookError(fn) {
+  return {
+    message: `React Hook "${fn}" cannot be called in an async function.`,
+  };
+}
+
 // For easier local testing
 if (!process.env.CI) {
   let only = [];

packages/eslint-plugin-react-hooks/src/RulesOfHooks.js

@@ -485,6 +485,17 @@ export default {
             // Pick a special message depending on the scope this hook was
             // called in.
             if (isDirectlyInsideComponentOrHook) {
+              // Report an error if the hook is called inside an async function.
+              const isAsyncFunction = codePathNode.async;
+              if (isAsyncFunction) {
+                context.report({
+                  node: hook,
+                  message:
+                    `React Hook "${context.getSource(hook)}" cannot be ` +
+                    'called in an async function.',
+                });
+              }
+
               // Report an error if a hook does not reach all finalizing code
               // path segments.
               //