Adapt ParametersNode#signature to ErrorRecoveryNode

No need to list them all out anymore, it's just a single possibility now

Author: Earlopain

lib/prism/node_ext.rb

@@ -329,10 +329,7 @@ def signature
         case param
         when MultiTargetNode
           names << [:req]
-        when NoKeywordsParameterNode, KeywordRestParameterNode,
-            NoBlockParameterNode, BlockParameterNode,
-            ForwardingParameterNode
-          # Invalid syntax, e.g. "def f(**nil, ...)" moves the NoKeywordsParameterNode to posts
+        when ErrorRecoveryNode
           raise "Invalid syntax"
         else
           names << [:req, param.name]

test/prism/ruby/parameters_signature_test.rb

@@ -77,6 +77,13 @@ def test_forwarding
       assert_parameters([[:rest, :*], [:keyrest, :**], [:block, :&]], "...")
     end
 
+    def test_invalid_syntax
+      e = assert_raise(RuntimeError) do
+        Prism.parse_statement("def f(**nil, ...); end").parameters.signature
+      end
+      assert_equal("Invalid syntax", e.message)
+    end
+
     private
 
     def assert_parameters(expected, source, compare: true)