Allow formatting code with different base level of indentation

lib/rufo/formatter.rb

@@ -4,6 +4,7 @@ class Rufo::Formatter
   include Rufo::Settings
 
   INDENT_SIZE = 2
+  DEFAULT_BASE_INDENTATION = 0
   EMPTY_STRING = [:string_literal, [:string_content]]
   EMPTY_HASH = [:hash, nil]
 
@@ -171,6 +172,8 @@ def initialize(code, **options)
     # can be added appropriately for heredocs for example.
     @literal_elements_level = nil
 
+    @base_indentation = options.delete(:base_indentation) || DEFAULT_BASE_INDENTATION
+
     init_settings(options)
   end
 
@@ -186,6 +189,9 @@ def format
     remove_lines_before_inline_declarations
     @output.lstrip!
     @output = "\n" if @output.empty?
+    if @base_indentation > 0
+      insert_base_indent(@base_indentation)
+    end
   end
 
   def visit(node)
@@ -4214,4 +4220,13 @@ def block_arg_type(node)
       node
     end
   end
+
+  def insert_base_indent(identation)
+    spaces = " " * identation
+    lines = @output.lines
+    lines.each do |line|
+      line.insert(0, spaces)
+    end
+    @output = lines.join
+  end
 end

spec/lib/rufo/formatter_spec.rb

@@ -111,4 +111,41 @@ def assert_format(code, expected = code, **options)
       }.to raise_error(Rufo::UnknownSyntaxError)
     end
   end
+
+  describe "base_indentation option" do
+    it "formats with different indentation levels" do
+      source = <<~SOURCE
+        def foo
+          puts "a"
+        end
+      SOURCE
+
+      # default identation level
+      expect(Rufo.format(source)).to eq source
+
+      # level 2
+      expected = <<-EXPECTED
+  def foo
+    puts "a"
+  end
+      EXPECTED
+      expect(Rufo.format(source, base_indentation: 2)).to eq expected
+
+      # level 4
+      expected = <<-EXPECTED
+    def foo
+      puts "a"
+    end
+      EXPECTED
+      expect(Rufo.format(source, base_indentation: 4)).to eq expected
+
+      # level 6
+      expected = <<-EXPECTED
+      def foo
+        puts "a"
+      end
+      EXPECTED
+      expect(Rufo.format(source, base_indentation: 6)).to eq expected
+    end
+  end
 end