[Fix] prop-types: handle anonymous functions

Fixes #2728.

Co-authored-by: Odin Hørthe Omdal <odin.omdal@gmail.com>
Co-authored-by: Dmitriy Lazarev <w@kich.dev>
Co-authored-by: Jordan Harband <ljharb@gmail.com>
Co-authored-by: Johnny Zabala <jzabala.s@gmail.com>

lib/util/Components.js

@@ -689,7 +689,7 @@ function componentRule(rule, context) {
     getStatelessComponent(node) {
       if (
         node.type === 'FunctionDeclaration'
-        && isFirstLetterCapitalized(node.id.name)
+        && (!node.id || isFirstLetterCapitalized(node.id.name))
         && utils.isReturningJSXOrNull(node)
       ) {
         return node;

tests/lib/rules/prop-types.js

@@ -2569,6 +2569,11 @@ ruleTester.run('prop-types', rule, {
         return null;
       }`,
       parser: parsers.TYPESCRIPT_ESLINT
+    },
+    {
+      code: `
+      export default function() {}
+      `
     }
   ],
 
@@ -5161,6 +5166,16 @@ ruleTester.run('prop-types', rule, {
       errors: [{
         message: '\'value\' is missing in props validation'
       }]
+    },
+    {
+      code: `
+        export default function ({ value = 'World' }) {
+          return <h1>Hello {value}</h1>
+        }
+      `,
+      errors: [{
+        message: '\'value\' is missing in props validation'
+      }]
     }
   ]
 });