Experimental: Add support for pairs in @genType.import to encode rena…

…me information.

Instead of typing
```
[@genType.import "foo"]
[@genType.as "bar"]
```
support the use of
```
[@genType.import ("foo", "bar")]
```

See #117.

examples/typescript-react-example/src/TestImport.gen.tsx

@@ -12,6 +12,8 @@ import {TopLevelClass as TopLevelClass} from './MyBanner';
 
 import * as React from 'react';
 
+import {default as defaultValue2NotChecked} from './exportNestedValues';
+
 // tslint:disable-next-line:no-var-requires
 const ReasonReact = require('reason-react/src/ReasonReact.js');
 
@@ -50,5 +52,11 @@ export function MyBannerInternalTypeChecked(props: Props) {
 // Export 'make' early to allow circular import from the '.bs.js' file.
 export const make: unknown = function _(show: any, message: any, children: any) { return ReasonReact.wrapJsForReason(TopLevelClass.MiddleLevelElements.MyBannerInternal, {show: show, message: (message == null ? message : {text:message[0]})}, children); };
 
+// In case of type error, check the type of 'defaultValue2' in 'TestImport.re' and './exportNestedValues'.
+export const defaultValue2TypeChecked: number = defaultValue2NotChecked;
+
+// Export 'defaultValue2' early to allow circular import from the '.bs.js' file.
+export const defaultValue2: unknown = defaultValue2TypeChecked as number;
+
 // tslint:disable-next-line:interface-over-type-literal
 export type message = { readonly text: string };

examples/typescript-react-example/src/TestImport.re

@@ -39,4 +39,8 @@ external make:
   ) =
   "";
 
-let make = make;
+let make = make;
+
+[@genType.import ("./exportNestedValues", "default")]
+[@bs.module "./TestImport.gen"]
+external defaultValue2: int = "";

src/Annotation.re

@@ -112,7 +112,22 @@ let getAttributeImportRenaming = attributes => {
   let attributeImport = attributes |> getAttributePayload(tagIsGenTypeImport);
   let attributeRenaming = attributes |> getAttributeRenaming;
   switch (attributeImport, attributeRenaming) {
-  | (Some(StringPayload(s)), _) => (Some(s), attributeRenaming)
+  | (Some(StringPayload(importString)), _) => (
+      Some(importString),
+      attributeRenaming,
+    )
+  | (
+      Some(
+        TuplePayload([
+          StringPayload(importString),
+          StringPayload(renameString),
+        ]),
+      ),
+      _,
+    ) => (
+      Some(importString),
+      Some(renameString),
+    )
   | _ => (None, attributeRenaming)
   };
 };