gui2/twml_error: Handle an optional list of faulty files separately

This allows us to be more self-contained and require less logic in the
instantiation site for preparing the report for display.

This requires adding a new row and label for displaying the list of
faulty files, which will be hidden when the list is empty or not
provided in the display() static member function.

data/gui/default/window/wml_error.cfg

@@ -58,6 +58,22 @@
 
 			[/row]
 
+			[row]
+
+				[column]
+					border = "all"
+					border_size = 5
+					horizontal_alignment = "left"
+
+					[label]
+						id = "files"
+						definition = "default"
+						wrap = true
+					[/label]
+				[/column]
+
+			[/row]
+
 			[row]
 
 				[column]

src/gui/dialogs/wml_error.cpp

@@ -14,7 +14,30 @@
 
 #include "gui/dialogs/wml_error.hpp"
 
+#include "addon/info.hpp"
+#include "gui/auxiliary/find_widget.tpp"
+#include "gui/widgets/control.hpp"
 #include "gui/widgets/settings.hpp"
+#include "gui/widgets/window.hpp"
+#include "serialization/string_utils.hpp"
+
+namespace
+{
+
+std::string format_file_list(const std::vector<std::string>& files)
+{
+	if(files.empty()) {
+		return "";
+	}
+
+	if(files.size() == 1) {
+		return files.front();
+	}
+
+	return utils::bullet_list(files);
+}
+
+}
 
 namespace gui2
 {
@@ -32,6 +55,11 @@ namespace gui2
  * summary & & control & m &
  *         Label used for displaying a brief summary of the error(s). $
  *
+ * files & & control & m &
+ *         Label used to display the list of affected add-ons or files, if
+ *         applicable. It is hidden otherwise. It is recommended to place it
+ *         after the summary label. $
+ *
  * details & & control & m &
  *         Full report of the parser or preprocessor error(s) found. $
  *
@@ -40,10 +68,22 @@ namespace gui2
 
 REGISTER_DIALOG(wml_error)
 
-twml_error::twml_error(const std::string& summary, const std::string& details)
+twml_error::twml_error(const std::string& summary,
+					   const std::vector<std::string>& files,
+					   const std::string& details)
+	: have_files_(!files.empty())
 {
 	register_label("summary", true, summary);
+	register_label("files", true, format_file_list(files));
 	register_label("details", true, details);
 }
 
+void twml_error::pre_show(CVideo& /*video*/, twindow& window)
+{
+    if(!have_files_) {
+		tcontrol& filelist = find_widget<tcontrol>(&window, "files", false);
+		filelist.set_visible(tcontrol::tvisible::invisible);
+	}
+}
+
 } // end namespace gui2

src/gui/dialogs/wml_error.hpp

@@ -22,19 +22,35 @@ namespace gui2 {
 class twml_error : public tdialog
 {
 public:
-    twml_error(const std::string& summary, const std::string& details);
+    twml_error(const std::string& summary,
+			   const std::vector<std::string>& files,
+			   const std::string& details);
 
 	/** The display function; see @ref tdialog for more information. */
 	static void display(const std::string& summary,
+						const std::vector<std::string>& files,
 						const std::string& details,
 						CVideo& video)
 	{
-		twml_error(summary, details).show(video);
+		twml_error(summary, files, details).show(video);
+	}
+
+	/** The display function; see @ref tdialog for more information. */
+	static void display(const std::string& summary,
+						const std::string& details,
+						CVideo& video)
+	{
+		display(summary, std::vector<std::string>(), details, video);
 	}
 
 private:
+	bool have_files_;
+
 	/** Inherited from tdialog, implemented by REGISTER_DIALOG. */
 	virtual const std::string& window_id() const;
+
+	/** Inherited from tdialog. */
+	void pre_show(CVideo& video, twindow& window);
 };
 
 }  // end namespace gui2