Treat type alias declarationlike function declaration (#584)

joa · hzoo · commit 020d012c5549 · 2018-09-25T14:39:43.000-04:00
A type alias shouldn't trigger a no-use-before-define warning just like a function declaration. Cyclic type dependencies are common when using flow. For instance: type Node<T> = { head: T; tail: Node<T> } Fixes #485
diff --git a/lib/babylon-to-espree/toAST.js b/lib/babylon-to-espree/toAST.js
@@ -72,6 +72,15 @@ var astTransformVisitor = {
       delete node.bound;
     }
 
+    if (path.isTypeAlias()) {
+      node.type = "FunctionDeclaration";
+      node.generator = false;
+      node.async = false;
+      node.expression = false;
+      node.params = [];
+      node.body = node.right;
+    }
+
     // flow: prevent "no-undef"
     // for "Component" in: "let x: React.Component"
     if (path.isQualifiedTypeIdentifier()) {
diff --git a/test/non-regression.js b/test/non-regression.js
@@ -1091,6 +1091,18 @@ describe("verify", () => {
         { "no-unused-vars": 1, "no-undef": 1 }
       );
     });
+
+    it("cyclic type dependencies #485", () => {
+      verifyAndAssertMessages(
+        unpad(`
+          type Node<T> = { head: T, tail: Node<T> };
+          type A = B[];
+          type B = number;
+        `),
+        { "no-use-before-define": 1 },
+        []
+      );
+    });
   });
 
   it("class usage", () => {
