Fix weirdness with parsing undefined as an identifier.

Author: joshwilsonvu

docs/no-react-deps.md

@@ -80,6 +80,11 @@ createEffect((prev) => {
   return (prev || 0) + 1;
 });
 
+createEffect((prev) => {
+  console.log(signal());
+  return prev ? prev + 1 : 1;
+}, undefined);
+
 const value = createMemo(() => computeExpensiveValue(a(), b()));
 
 const sum = createMemo((prev) => input() + prev, 0);

docs/reactivity.md

@@ -537,6 +537,11 @@ createEffect(() => {
   runWithOwner(owner, () => console.log(signal()));
 });
 
+const [signal] = createSignal();
+createEffect(() => {
+  runWithOwner(undefined, () => console.log(signal()));
+});
+
 const [signal] = createSignal();
 createEffect(() => {
   [1, 2].forEach(() => console.log(signal()));

src/utils.ts

@@ -50,7 +50,9 @@ export function trace(node: T.Node, initialScope: TSESLint.Scope.Scope): T.Node
     if (!variable) return node;
 
     const def = variable.defs[0];
-    switch (def.type) {
+
+    // def is `undefined` for Identifier `undefined`
+    switch (def?.type) {
       case "FunctionName":
       case "ClassName":
       case "ImportBinding":

test/rules/no-react-deps.test.ts

@@ -14,6 +14,10 @@ export const cases = run("no-react-deps", rule, {
       console.log(signal());
       return (prev || 0) + 1;
     });`,
+    `createEffect((prev) => {
+      console.log(signal());
+      return prev ? prev + 1 : 1;
+    }, undefined);`,
     `const value = createMemo(() => computeExpensiveValue(a(), b()));`,
     `const sum = createMemo((prev) => input() + prev, 0);`,
     `const args = [() => { console.log(signal()); }, [signal()]];

test/rules/reactivity.test.ts

@@ -95,6 +95,10 @@ export const cases = run("reactivity", rule, {
       const owner = getOwner();
       runWithOwner(owner, () => console.log(signal()));
     });`,
+    `const [signal] = createSignal();
+    createEffect(() => {
+      runWithOwner(undefined, () => console.log(signal()));
+    });`,
     // Sync callbacks
     `const [signal] = createSignal();
     createEffect(() => {