[Fix] Fix detection of annotated props with default value

Fixes #2298

lib/util/annotations.js

@@ -17,9 +17,11 @@ function isAnnotatedFunctionPropsDeclaration(node, context) {
     return false;
   }
 
-  const tokens = context.getFirstTokens(node.params[0], 2);
-  const isAnnotated = node.params[0].typeAnnotation;
-  const isDestructuredProps = node.params[0].type === 'ObjectPattern';
+  const typeNode = node.params[0].type === 'AssignmentPattern' ? node.params[0].left : node.params[0];
+
+  const tokens = context.getFirstTokens(typeNode, 2);
+  const isAnnotated = typeNode.typeAnnotation;
+  const isDestructuredProps = typeNode.type === 'ObjectPattern';
   const isProps = tokens[0].value === 'props' || (tokens[1] && tokens[1].value === 'props');
 
   return (isAnnotated && (isDestructuredProps || isProps));

lib/util/propTypes.js

@@ -200,7 +200,7 @@ module.exports = function propTypesInstructions(context, components, utils) {
    * @returns {ASTNode} The resolved type annotation for the node.
    */
   function resolveTypeAnnotation(node) {
-    let annotation = node.typeAnnotation || node;
+    let annotation = (node.left && node.left.typeAnnotation) || node.typeAnnotation || node;
     while (annotation && (annotation.type === 'TypeAnnotation' || annotation.type === 'NullableTypeAnnotation')) {
       annotation = annotation.typeAnnotation;
     }

tests/lib/rules/prop-types.js

@@ -2336,6 +2336,19 @@ ruleTester.run('prop-types', rule, {
           foo: PropTypes.number,
         }
       `
+    },
+    {
+      // issue #2298
+      code: `
+      type Props = {|
+        firstname?: string
+      |};
+
+      function Hello({ firstname = 'John' }: Props = {}) {
+        return <div>Hello {firstname}</div>
+      }
+      `,
+      parser: parsers.BABEL_ESLINT
     }
   ],
 
@@ -4621,6 +4634,22 @@ ruleTester.run('prop-types', rule, {
       errors: [{
         message: '\'initialValues\' is missing in props validation'
       }]
+    },
+    {
+      // issue #2298
+      code: `
+        type Props = {|
+          firstname?: string
+        |};
+
+        function Hello({ firstname = 'John', lastname = 'Doe' }: Props = {}) {
+          return <div>Hello {firstname} {lastname}</div>
+        }
+      `,
+      parser: parsers.BABEL_ESLINT,
+      errors: [{
+        message: '\'lastname\' is missing in props validation'
+      }]
     }
   ]
 });