Complete writer methods with self receiver when receiver is self (#3550)

* fix: Complete writer methods with self receiver when appropriate

Fixes completion of setter methods to use 'self.method=' syntax when
accessed within instance methods. Previously, completion would suggest
'method=' which assigns to a local variable instead of calling the
instance writer method.

* feat: Add spacing around = in writer method completions

Writer method completions now include proper spacing around the equals
sign to follow Ruby style conventions (e.g., 'self.attr = ' instead
of 'self.attr=').

Author: antw

lib/ruby_lsp/listeners/completion.rb

@@ -516,6 +516,14 @@ def complete_methods(node, name)
 
           entry_name = entry.name
           owner_name = entry.owner&.name
+          new_text = entry_name
+
+          if entry_name.end_with?("=")
+            method_name = entry_name.delete_suffix("=")
+
+            # For writer methods, format as assignment and prefix "self." when no receiver is specified
+            new_text = node.receiver.nil? ? "self.#{method_name} = " : "#{method_name} = "
+          end
 
           label_details = Interface::CompletionItemLabelDetails.new(
             description: entry.file_name,
@@ -525,7 +533,7 @@ def complete_methods(node, name)
             label: entry_name,
             filter_text: entry_name,
             label_details: label_details,
-            text_edit: Interface::TextEdit.new(range: range, new_text: entry_name),
+            text_edit: Interface::TextEdit.new(range: range, new_text: new_text),
             kind: Constant::CompletionItemKind::METHOD,
             data: {
               owner_name: owner_name,

test/requests/completion_test.rb

@@ -687,12 +687,17 @@ class Foo
 
         def bar
           q
+          self.q
         end
       end
+
+      foo = Foo.new
+      foo.q
     RUBY
 
     with_server(source) do |server, uri|
       with_file_structure(server) do
+        # Test implicit self receiver: "q"
         server.process_message(id: 1, method: "textDocument/completion", params: {
           textDocument: { uri: uri },
           position: { line: 4, character: 5 },
@@ -701,7 +706,29 @@ def bar
         result = server.pop_response.response
         assert_equal(["qux", "qux="], result.map(&:label))
         assert_equal(["qux", "qux="], result.map(&:filter_text))
-        assert_equal(["qux", "qux="], result.map { |completion| completion.text_edit.new_text })
+        assert_equal(["qux", "self.qux = "], result.map { |completion| completion.text_edit.new_text })
+
+        # Test explicit self receiver: "self.q"
+        server.process_message(id: 1, method: "textDocument/completion", params: {
+          textDocument: { uri: uri },
+          position: { line: 5, character: 10 },
+        })
+
+        result = server.pop_response.response
+        assert_equal(["qux", "qux="], result.map(&:label))
+        assert_equal(["qux", "qux="], result.map(&:filter_text))
+        assert_equal(["qux", "qux = "], result.map { |completion| completion.text_edit.new_text })
+
+        # Test external receiver; "foo.q"
+        server.process_message(id: 1, method: "textDocument/completion", params: {
+          textDocument: { uri: uri },
+          position: { line: 10, character: 5 },
+        })
+
+        result = server.pop_response.response
+        assert_equal(["qux", "qux="], result.map(&:label))
+        assert_equal(["qux", "qux="], result.map(&:filter_text))
+        assert_equal(["qux", "qux = "], result.map { |completion| completion.text_edit.new_text })
       end
     end
   end