[ruby/irb] Refactor RubyLex and its tests

(https://github.com/ruby/irb/pull/427)

* Make sure `RubyLex#set_input`'s context is always present in tests

In real-world scenarios, the context should always be non-nil:
https://github.com/ruby/irb/blob/master/lib/irb.rb#L489

So we should make sure our test setup reflects that.

* Make context a required keyword

Since in practice, `set_input`'s context should always be non-nil, its
parameters should reflect that.

And since `RubyLex#check_state` is only called by `#lex` and
`#set_input`, both of which now always require context, we can assume
its context should be non-nil too.

https://github.com/ruby/irb/commit/1aeeb86203

lib/irb/ruby-lex.rb

@@ -48,7 +48,7 @@ class RubyLex
   end
 
   # io functions
-  def set_input(io, p = nil, context: nil, &block)
+  def set_input(io, p = nil, context:, &block)
     @io = io
     if @io.respond_to?(:check_termination)
       @io.check_termination do |code|
@@ -216,7 +216,7 @@ class RubyLex
     ltype = process_literal_type(tokens)
     indent = process_nesting_level(tokens)
     continue = process_continue(tokens)
-    lvars_code = self.class.generate_local_variables_assign_code(context&.local_variables || [])
+    lvars_code = self.class.generate_local_variables_assign_code(context.local_variables)
     code = "#{lvars_code}\n#{code}" if lvars_code
     code_block_open = check_code_block(code, tokens)
     [ltype, indent, continue, code_block_open]

test/irb/test_ruby_lex.rb

@@ -24,13 +24,14 @@ module TestIRB
       last_line_index = lines.length - 1
       byte_pointer = lines.last.length
 
+      context = build_context
+      context.auto_indent_mode = true
       ruby_lex = RubyLex.new()
       io = MockIO_AutoIndent.new([lines, last_line_index, byte_pointer, add_new_line]) do |auto_indent|
         error_message = "Calculated the wrong number of spaces for:\n #{lines.join("\n")}"
         assert_equal(correct_space_count, auto_indent, error_message)
       end
-      ruby_lex.set_input(io)
-      context = OpenStruct.new(auto_indent_mode: true)
+      ruby_lex.set_input(io, context: context)
       ruby_lex.set_auto_indent(context)
     end
 
@@ -48,11 +49,10 @@ module TestIRB
 
     def ruby_lex_for_lines(lines, local_variables: [])
       ruby_lex = RubyLex.new()
+
+      context = build_context(local_variables)
       io = proc{ lines.join("\n") }
-      ruby_lex.set_input(io, io)
-      unless local_variables.empty?
-        context = OpenStruct.new(local_variables: local_variables)
-      end
+      ruby_lex.set_input(io, io, context: context)
       ruby_lex.lex(context)
       ruby_lex
     end
@@ -620,7 +620,8 @@ module TestIRB
       ruby_lex.set_prompt do |ltype, indent, continue, line_no|
         '%03d:%01d:%1s:%s ' % [line_no, indent, ltype, continue ? '*' : '>']
       end
-      ruby_lex.set_input(io)
+      context = build_context
+      ruby_lex.set_input(io, context: context)
     end
 
     def test_dyanmic_prompt
@@ -697,5 +698,19 @@ module TestIRB
         assert_equal('<<A', string_literal&.tok)
       end
     end
+
+    private
+
+    def build_context(local_variables = nil)
+      workspace = IRB::WorkSpace.new
+
+      if local_variables
+        local_variables.each do |n|
+          workspace.binding.local_variable_set(n, nil)
+        end
+      end
+
+      IRB::Context.new(nil, workspace)
+    end
   end
 end