From b2638263d3ad49cccbbf2088834f6d6252b4eb9d Mon Sep 17 00:00:00 2001
From: Daniel Tschinder <daniel.tschinder@researchgate.net>
Date: Sun, 22 Oct 2017 22:47:33 +0200
Subject: [PATCH 1/2] Resolve flow $Keys to union type

---
 src/utils/__tests__/getFlowType-test.js | 15 ++++++++++++++
 src/utils/getFlowType.js                | 26 +++++++++++++++++++++++++
 src/utils/resolveObjectKeysToArray.js   |  4 ++--
 3 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/src/utils/__tests__/getFlowType-test.js b/src/utils/__tests__/getFlowType-test.js
index 675c7919164..ef0a06d881c 100644
--- a/src/utils/__tests__/getFlowType-test.js
+++ b/src/utils/__tests__/getFlowType-test.js
@@ -248,4 +248,19 @@ describe('getFlowType', () => {
       it(type, () => test(type, types[type]));
     });
   });
+
+  it('resolves $Keys to union', () => {
+    var typePath = statement(`
+      var x: $Keys<typeof CONTENTS> = 2;
+      const CONTENTS = {
+        'apple': '🍎',
+        'banana': '🍌',
+      };
+    `).get('declarations', 0).get('id').get('typeAnnotation').get('typeAnnotation');
+
+    expect(getFlowType(typePath)).toEqual({name: 'union', elements: [
+      { name: 'literal', value: "'apple'" },
+      { name: 'literal', value: "'banana'" },
+    ], raw: '$Keys<typeof CONTENTS>'});
+  });
 });
diff --git a/src/utils/getFlowType.js b/src/utils/getFlowType.js
index e6209dc9e2d..a49ad29ac6c 100644
--- a/src/utils/getFlowType.js
+++ b/src/utils/getFlowType.js
@@ -17,6 +17,7 @@ import printValue from './printValue';
 import recast from 'recast';
 import getTypeAnnotation from '../utils/getTypeAnnotation';
 import resolveToValue from '../utils/resolveToValue';
+import { resolveObjectExpressionToNameArray } from '../utils/resolveObjectKeysToArray';
 
 const { types: { namedTypes: types } } = recast;
 
@@ -54,7 +55,32 @@ function getFlowTypeWithRequirements(path: NodePath): FlowTypeDescriptor {
   return type;
 }
 
+function handleKeysHelper(path: NodePath) {
+  let value = path.get('typeParameters', 'params', 0);
+  if (types.TypeofTypeAnnotation.check(value.node)) {
+    value = value.get('argument', 'id');
+  } else {
+    value = value.get('id');
+  }
+  const resolvedPath = resolveToValue(value);
+  if (resolvedPath && types.ObjectExpression.check(resolvedPath.node)) {
+    const keys = resolveObjectExpressionToNameArray(resolvedPath, true);
+
+    if (keys) {
+      return {
+        name: 'union',
+        raw: printValue(path),
+        elements: keys.map(value => ({ name: 'literal', value })),
+      };
+    }
+  }
+}
+
 function handleGenericTypeAnnotation(path: NodePath) {
+  if (path.node.id.name === '$Keys' && path.node.typeParameters) {
+    return handleKeysHelper(path);
+  }
+
   let type;
   if (types.QualifiedTypeIdentifier.check(path.node.id)) {
     type = handleQualifiedTypeIdentifier(path.get('id'));
diff --git a/src/utils/resolveObjectKeysToArray.js b/src/utils/resolveObjectKeysToArray.js
index a9527a648c2..15242e6bd00 100644
--- a/src/utils/resolveObjectKeysToArray.js
+++ b/src/utils/resolveObjectKeysToArray.js
@@ -32,7 +32,7 @@ function isObjectKeysCall(node: ASTNode): bool {
     node.callee.property.name === 'keys';
 }
 
-function resolveObjectExpressionToNameArray(objectExpression: NodePath): ?Array<string> {
+export function resolveObjectExpressionToNameArray(objectExpression: NodePath, raw: boolean = false): ?Array<string> {
   if (
     types.ObjectExpression.check(objectExpression.value) &&
     objectExpression.value.properties.every(
@@ -53,7 +53,7 @@ function resolveObjectExpressionToNameArray(objectExpression: NodePath): ?Array<
 
       if (types.Property.check(prop)) {
         // Key is either Identifier or Literal
-        const name = prop.key.name || prop.key.value;
+        const name = prop.key.name || (raw ? prop.key.raw : prop.key.value);
 
         values.push(name);
       } else if (types.SpreadProperty.check(prop)) {

From 95f52bb221f14f3cbfdbda49264b2f8fd6b35a3a Mon Sep 17 00:00:00 2001
From: Daniel Tschinder <daniel.tschinder@researchgate.net>
Date: Sun, 22 Oct 2017 22:48:39 +0200
Subject: [PATCH 2/2] Add one more test without typeof

---
 src/utils/__tests__/getFlowType-test.js | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/utils/__tests__/getFlowType-test.js b/src/utils/__tests__/getFlowType-test.js
index ef0a06d881c..4e6c9202a00 100644
--- a/src/utils/__tests__/getFlowType-test.js
+++ b/src/utils/__tests__/getFlowType-test.js
@@ -263,4 +263,19 @@ describe('getFlowType', () => {
       { name: 'literal', value: "'banana'" },
     ], raw: '$Keys<typeof CONTENTS>'});
   });
+
+  it('resolves $Keys without typeof to union', () => {
+    var typePath = statement(`
+      var x: $Keys<CONTENTS> = 2;
+      const CONTENTS = {
+        'apple': '🍎',
+        'banana': '🍌',
+      };
+    `).get('declarations', 0).get('id').get('typeAnnotation').get('typeAnnotation');
+
+    expect(getFlowType(typePath)).toEqual({name: 'union', elements: [
+      { name: 'literal', value: "'apple'" },
+      { name: 'literal', value: "'banana'" },
+    ], raw: '$Keys<CONTENTS>'});
+  });
 });