[Writer] Preserve an empty line between declarations and members

lib/ruby/signature/writer.rb

@@ -37,11 +37,8 @@ def write_comment(comment, level:)
       end
 
       def write(decls)
-        decls.each.with_index do |decl, index|
-          if index > 0
-            out.puts
-          end
-
+        [nil, *decls].each_cons(2) do |prev, decl|
+          preserve_empty_line(prev, decl)
           write_decl decl
         end
       end
@@ -56,10 +53,8 @@ def write_decl(decl)
           write_annotation decl.annotations, level: 0
           out.puts "class #{name_and_params(decl.name, decl.type_params)}#{super_class}"
 
-          decl.members.each.with_index do |member, index|
-            if index > 0
-              out.puts
-            end
+          [nil, *decl.members].each_cons(2) do |prev, member|
+            preserve_empty_line prev, member
             write_member member
           end
 
@@ -251,6 +246,24 @@ def attribute(kind, attr)
               end
         "attr_#{kind} #{attr.name}#{var}: #{attr.type}"
       end
+
+      def preserve_empty_line(prev, decl)
+        return unless prev
+
+        # When the signature is not constructed by the parser,
+        # it always inserts an empty line.
+        unless prev.location
+          out.puts
+          return
+        end
+
+        prev_end_line = prev.location.end_line
+        decl = decl.comment if decl.respond_to?(:comment) && decl.comment
+        start_line = decl.location.start_line
+        if start_line - prev_end_line > 1
+          out.puts
+        end
+      end
     end
   end
 end

test/ruby/signature/writer_test.rb

@@ -6,15 +6,19 @@ class Ruby::Signature::WriterTest < Minitest::Test
   Parser = Ruby::Signature::Parser
   Writer = Ruby::Signature::Writer
 
-  def assert_writer(sig)
-    Parser.parse_signature(sig).tap do |decls|
+  def format(sig)
+    Parser.parse_signature(sig).then do |decls|
       writer = Writer.new(out: StringIO.new)
       writer.write(decls)
 
-      assert_equal sig, writer.out.string
+      writer.out.string
     end
   end
 
+  def assert_writer(sig)
+    assert_equal sig, format(sig)
+  end
+
   def test_const_decl
     assert_writer <<-SIG
 # World to world.
@@ -136,4 +140,79 @@ class Foo[out A, unchecked B, in C] < Bar[A, C, B]
 end
     SIG
   end
+
+  def test_preserve_empty_line
+    assert_writer <<-SIG
+class Foo
+  def initialize: () -> void
+  def foo: () -> void
+
+  def bar: () -> void
+  # comment
+  def self.foo: () -> void
+
+  # comment
+  def baz: () -> void
+end
+module Bar
+end
+
+class OneEmptyLine
+end
+
+# comment
+class C
+end
+# comment
+class D
+end
+    SIG
+  end
+
+  def test_remove_double_empty_lines
+    src = <<-SIG
+class Foo
+
+  def foo: () -> void
+
+
+  def bar: () -> void
+end
+
+
+module Bar
+
+
+  def foo: () -> void
+end
+    SIG
+
+    expected = <<-SIG
+class Foo
+  def foo: () -> void
+
+  def bar: () -> void
+end
+
+module Bar
+  def foo: () -> void
+end
+    SIG
+
+    assert_equal expected, format(src)
+
+  end
+
+  def test_smoke
+    Pathname.glob('stdlib/**/*.rbs').each do |path|
+      orig_decls = Ruby::Signature::Parser.parse_signature(path.read)
+
+      io = StringIO.new
+      w = Ruby::Signature::Writer.new(out: io)
+      w.write(orig_decls)
+      decls = Ruby::Signature::Parser.parse_signature(io.string)
+
+      assert_equal orig_decls, decls
+    end
+  end
 end