Restore auto-select on return, add a flag to disable that for commands

Fixes #3849 Again

src/command_manager.cc

@@ -630,7 +630,9 @@ Completions CommandManager::complete_command_name(const Context& context, String
     auto aliases = context.aliases().flatten_aliases()
             | transform(&HashItem<String, String>::key);
 
-    return {0, query.length(), Kakoune::complete(query, query.length(), concatenated(commands, aliases)), Completions::Flags::Menu};
+    return {0, query.length(),
+            Kakoune::complete(query, query.length(), concatenated(commands, aliases)),
+            Completions::Flags::Menu | Completions::Flags::NoEmpty};
 }
 
 Completions CommandManager::complete_module_name(StringView query) const

src/completion.hh

@@ -22,7 +22,8 @@ struct Completions
     {
         None = 0,
         Quoted = 0b1,
-        Menu = 0b10
+        Menu = 0b10,
+        NoEmpty = 0b100
     };
 
     constexpr friend bool with_bit_ops(Meta::Type<Flags>) { return true; }

src/input_handler.cc

@@ -775,7 +775,10 @@ public:
             const bool has_completions = not m_completions.candidates.empty();
             const bool completion_selected = m_current_completion != -1;
             const bool text_entered = m_completions.start != line.byte_count_to(m_line_editor.cursor_pos());
-            return has_completions and not completion_selected and text_entered;
+            return (m_completions.flags & Completions::Flags::Menu) and
+                has_completions and
+                not completion_selected and
+                (not (m_completions.flags & Completions::Flags::NoEmpty) or text_entered);
         };
 
         if (key == Key::Return)
@@ -997,7 +1000,6 @@ public:
         else
         {
             if (key == ' ' and
-                (m_completions.flags & Completions::Flags::Menu) and
                 not (m_completions.flags & Completions::Flags::Quoted) and // if token is quoted, this space does not end it
                 can_auto_insert_completion())
                 m_line_editor.insert_from(line.char_count_to(m_completions.start),