$ElementType now accepts reference to the key

src/collector/globals.js

@@ -39,13 +39,13 @@ function elemType(params: (?Type)[], resolve: TypeId => Type): ?Type {
 
     invariant(record.kind === 'record');
 
-    // TODO: support for references.
-    invariant(key.kind === 'literal');
-    invariant(typeof key.value === 'string');
+    const prop = key.kind === 'reference' ? resolve(key.to) : key;
 
-    const field = wu(record.fields).find(field => field.name === key.value);
+    invariant(prop.kind === 'literal');
+    invariant(typeof prop.value === 'string');
+
+    const field = wu(record.fields).find(field => field.name === prop.value);
 
-    // TODO: what about removing "id"?
     return field ? t.clone(field.value) : null;
 }
 

tests/samples/elementType/source.js

@@ -2,8 +2,11 @@ type X<T> = {
     x: T | string,
 };
 
+type P = 'x';
+
 type Y<T> = {
     y: $ElementType<X<boolean>, T>,
+    yy: $ElementType<X<boolean>, P>,
 };
 
 type Z = $PropertyType<Y<'x'>, 'y'>;

tests/samples/elementType/types.yaml

@@ -8,6 +8,9 @@
             - {kind: string}
         required: true
     id: [elementType, X, boolean]
+-   kind: literal
+    value: x
+    id: [elementType, P]
 -   kind: record
     fields:
     -   name: y
@@ -17,6 +20,13 @@
             - {kind: boolean}
             - {kind: string}
         required: true
+    -   name: yy
+        value:
+            kind: union
+            variants:
+            - {kind: boolean}
+            - {kind: string}
+        required: true
     id: [elementType, Y, x]
 -   kind: union
     variants: