[flow] Process polymorphic type bounds on functions (#444)

Author: rattrayalex

index.js

@@ -176,6 +176,18 @@ function monkeypatch() {
     }
   }
 
+  function visitTypeParameters(typeParameters) {
+    var params = typeParameters.params;
+
+    // visit bounds on polymorphpic types, eg; `Foo` in `fn<T: Foo>(a: T): T`
+    for (var i = 0; i < params.length; i++) {
+      var param = params[i];
+      if (param.typeAnnotation) {
+        visitTypeAnnotation.call(this, param.typeAnnotation);
+      }
+    }
+  }
+
   function checkIdentifierOrVisit(node) {
     if (node.typeAnnotation) {
       visitTypeAnnotation.call(this, node.typeAnnotation);
@@ -249,6 +261,7 @@ function monkeypatch() {
     var typeParamScope;
     if (node.typeParameters) {
       typeParamScope = nestTypeParamScope(this.scopeManager, node);
+      visitTypeParameters.call(this, node.typeParameters);
     }
     if (node.returnType) {
       checkIdentifierOrVisit.call(this, node.returnType);

test/non-regression.js

@@ -222,13 +222,13 @@ describe("verify", () => {
       );
     });
 
-    it("type parameters", () => {
+    it("type parameter bounds", () => {
       verifyAndAssertMessages(
         unpad(`
           import type Foo from 'foo';
           import type Foo2 from 'foo';
-          function log<T1, T2>(a: T1, b: T2) { return a + b; }
-          log<Foo, Foo2>(1, 2);
+          function log<T1: Foo, T2: Foo2>(a: T1, b: T2) { return a + b; }
+          log(1, 2);
         `),
         { "no-unused-vars": 1, "no-undef": 1 },
         []