Ensure lambda block-local variables are handled properly

Author: kddnewton

lib/syntax_tree/parser.rb

@@ -2054,11 +2054,10 @@ def lambda_locals(source)
       tokens[(index + 1)..].each_with_object([]) do |token, locals|
         (lineno, column), type, value, = token
 
-        # Make the state transition for the parser. This is going to raise a
-        # KeyError if we don't have a transition for the current state and type.
-        # But that shouldn't actually be possible because ripper would have
-        # found a syntax error by then.
-        state = transitions[state].fetch(type)
+        # Make the state transition for the parser. If there isn't a transition
+        # from the current state to a new state for this type, then we're in a
+        # pattern that isn't actually locals. In that case we can return [].
+        state = transitions[state].fetch(type) { return [] }
 
         # If we hit an identifier, then add it to our list.
         next if type != :on_ident

test/fixtures/lambda.rb

@@ -66,3 +66,13 @@
 ) {}
 -
 ->(; a, b) {}
+%
+->(a = (b; c)) {}
+-
+->(
+  a = (
+    b
+    c
+  )
+) do
+end