LibGUI: Allow completion suggestions to fill and display different text

There are times when it is nice to display one suggestion but fill
something different. This lays the groundwork for allowing
GMLAutocompleteProvider to automatically add ': ' to the end of
suggested properties, while keeping the ': ' suffix from cluttering up
the suggestion UI.

Userland/DevTools/HackStudio/AutoCompleteResponse.h

@@ -22,6 +22,7 @@ inline bool encode(IPC::Encoder& encoder, const GUI::AutocompleteProvider::Entry
     encoder << (u64)response.partial_input_length;
     encoder << (u32)response.kind;
     encoder << (u32)response.language;
+    encoder << response.display_text;
     return true;
 }
 
@@ -34,7 +35,8 @@ inline bool decode(IPC::Decoder& decoder, GUI::AutocompleteProvider::Entry& resp
     bool ok = decoder.decode(response.completion)
         && decoder.decode(partial_input_length)
         && decoder.decode(kind)
-        && decoder.decode(language);
+        && decoder.decode(language)
+        && decoder.decode(response.display_text);
 
     if (ok) {
         response.kind = static_cast<GUI::AutocompleteProvider::CompletionKind>(kind);

Userland/Libraries/LibGUI/AutocompleteProvider.cpp

@@ -33,6 +33,7 @@ public:
         __ModelRoleCustom = (int)GUI::ModelRole::Custom,
         PartialInputLength,
         Kind,
+        Completion,
     };
 
     virtual int row_count(const GUI::ModelIndex& = GUI::ModelIndex()) const override { return m_suggestions.size(); }
@@ -42,7 +43,10 @@ public:
         auto& suggestion = m_suggestions.at(index.row());
         if (role == GUI::ModelRole::Display) {
             if (index.column() == Column::Name) {
-                return suggestion.completion;
+                if (!suggestion.display_text.is_empty())
+                    return suggestion.display_text;
+                else
+                    return suggestion.completion;
             }
             if (index.column() == Column::Icon) {
                 if (suggestion.language == GUI::AutocompleteProvider::Language::Cpp) {
@@ -67,6 +71,9 @@ public:
         if ((int)role == InternalRole::PartialInputLength)
             return (i64)suggestion.partial_input_length;
 
+        if ((int)role == InternalRole::Completion)
+            return suggestion.completion;
+
         return {};
     }
 
@@ -173,8 +180,8 @@ void AutocompleteBox::apply_suggestion()
     if (!selected_index.is_valid() || !m_suggestion_view->model()->is_within_range(selected_index))
         return;
 
-    auto suggestion_index = m_suggestion_view->model()->index(selected_index.row(), AutocompleteSuggestionModel::Column::Name);
+    auto suggestion_index = m_suggestion_view->model()->index(selected_index.row());
-    auto suggestion = suggestion_index.data().to_string();
+    auto suggestion = suggestion_index.data((GUI::ModelRole)AutocompleteSuggestionModel::InternalRole::Completion).to_string();
     size_t partial_length = suggestion_index.data((GUI::ModelRole)AutocompleteSuggestionModel::InternalRole::PartialInputLength).to_i64();
 
     VERIFY(suggestion.length() >= partial_length);

Userland/Libraries/LibGUI/AutocompleteProvider.h

@@ -37,6 +37,7 @@ public:
         size_t partial_input_length { 0 };
         CompletionKind kind { CompletionKind::Identifier };
         Language language { Language::Unspecified };
+        String display_text {};
     };
 
     struct ProjectLocation {