Add support for $Shape

src/globals.js

@@ -71,6 +71,28 @@ function stripMaybe(params: (?Type)[], resolve: TypeId => Type): ?Type {
     return clone(maybe.value);
 }
 
+function shape(params: (?Type)[], resolve: TypeId => Type): ?Type {
+    invariant(params.length === 1);
+
+    const [ref] = params;
+
+    invariant(ref && ref.kind === 'reference');
+
+    const record = resolve(ref.to);
+
+    invariant(record.kind === 'record');
+
+    const fields = wu(record.fields)
+        .map(clone)
+        .tap(field => field.required = false)
+        .toArray();
+
+    return {
+        kind: 'record',
+        fields,
+    };
+}
+
 export default {
     Object: object,
     Buffer: buffer,
@@ -79,4 +101,5 @@ export default {
     $PropertyType: elemType,
     $ElementType: elemType,
     $NonMaybeType: stripMaybe,
+    $Shape: shape,
 };

tests/samples/shape.js

@@ -0,0 +1,8 @@
+type X = {
+    x: string;
+    y: boolean;
+}
+
+type Y = $Shape<X>;
+
+export type {Y};

tests/samples/shape.json

@@ -0,0 +1,20 @@
+{
+    "types": [
+        {
+            "id": ["shape", "X"],
+            "kind": "record",
+            "fields": [
+                {"name": "x", "value": {"kind": "string"}, "required": true},
+                {"name": "y", "value": {"kind": "boolean"}, "required": true}
+            ]
+        },
+        {
+            "id": ["shape", "Y"],
+            "kind": "record",
+            "fields": [
+                {"name": "x", "value": {"kind": "string"}, "required": false},
+                {"name": "y", "value": {"kind": "boolean"}, "required": false}
+            ]
+        }
+    ]
+}