GUI2: minor refactoring of window construction to guard against memory leaks

This ensures the window object is managed by a smart pointer from the moment of its
creation, instead of being passed around as a raw pointer first. If an exception were
thrown during window creation, it would have resulted in a memory leak.

* Moved window_ member assignment to build_window() in both modal_dialog and modeless_dialog.
* Added an assertion after window creation in modeless_dialog.
* Renamed the global build() function to build_window_impl() to avoid confusion with
  builder_widget::build.

src/gui/core/window_builder.cpp

@@ -46,11 +46,11 @@ namespace gui2
  * be tuned. This page will describe what can be tuned.
  *
  */
-window* build(const builder_window::window_resolution* definition)
+window_ptr_t build_window_impl(const builder_window::window_resolution* definition)
 {
 	// We set the values from the definition since we can only determine the
 	// best size (if needed) after all widgets have been placed.
-	window* win = new window(definition);
+	window_ptr_t win = std::make_unique<window>(definition);
 	assert(win);
 
 	for(const auto& lg : definition->linked_groups) {
@@ -75,15 +75,15 @@ window* build(const builder_window::window_resolution* definition)
 		win->init_grid(definition->grid);
 	}
 
-	win->add_to_keyboard_chain(win);
+	win->add_to_keyboard_chain(win.get());
 
 	return win;
 }
 
-window* build(const std::string& type)
+window_ptr_t build_window_impl(const std::string& type)
 {
 	const builder_window::window_resolution& definition = get_window_builder(type);
-	window* window = build(&definition);
+	window_ptr_t window = build_window_impl(&definition);
 	window->set_id(type);
 	return window;
 }

src/gui/core/window_builder.hpp

@@ -14,28 +14,20 @@
 
 #pragma once
 
+#include "color.hpp"
 #include "gui/auxiliary/typed_formula.hpp"
 #include "gui/core/linked_group_definition.hpp"
 #include "gui/widgets/grid.hpp"
-#include "color.hpp"
-
 #include "utils/functional.hpp"
 
+#include <memory>
+
 class config;
 
 namespace gui2
 {
-
 class window;
 
-/**
- * Builds a window.
- *
- * @param type                    The type id string of the window, this window
- *                                must be registered at startup.
- */
-window* build(const std::string& type);
-
 /** Contains the info needed to instantiate a widget. */
 struct builder_widget
 {
@@ -211,9 +203,19 @@ private:
 	std::string description_;
 };
 
+using window_ptr_t = std::unique_ptr<window>;
+
 /**
  * Builds a window.
  */
-window* build(const builder_window::window_resolution* res);
+window_ptr_t build_window_impl(const builder_window::window_resolution* res);
+
+/**
+ * Builds a window.
+ *
+ * @param type                    The type id string of the window, this window
+ *                                must be registered at startup.
+ */
+window_ptr_t build_window_impl(const std::string& type);
 
 } // namespace gui2

src/gui/dialogs/modal_dialog.cpp

@@ -72,8 +72,7 @@ bool modal_dialog::show(const unsigned auto_close_time)
 		return false;
 	}
 
-	window_.reset(build_window());
-	assert(window_.get());
+	build_window();
 
 	post_build(*window_);
 
@@ -215,9 +214,10 @@ field_label* modal_dialog::register_label(const std::string& id,
 	return field;
 }
 
-window* modal_dialog::build_window() const
+void modal_dialog::build_window()
 {
-	return build(window_id());
+	window_ = build_window_impl(window_id());
+	assert(window_);
 }
 
 void modal_dialog::post_build(window& /*window*/)

src/gui/dialogs/modal_dialog.hpp

@@ -322,7 +322,7 @@ protected:
 
 protected:
 	/** The window object build for this dialog. */
-	std::unique_ptr<window> window_;
+	window_ptr_t window_;
 
 private:
 	/** Returns the window exit status, 0 means not shown. */
@@ -373,12 +373,10 @@ private:
 	/**
 	 * Builds the window.
 	 *
-	 * Every dialog shows it's own kind of window, this function should return
-	 * the window to show.
-	 *
-	 * @returns                   The window to show.
+	 * Every dialog shows its own kind of window. This function handles the building
+	 * of said window. @ref window_ should be non-null after this is called.
 	 */
-	window* build_window() const;
+	void build_window();
 
 	/**
 	 * Actions to be taken directly after the window is build.

src/gui/dialogs/modeless_dialog.cpp

@@ -41,7 +41,7 @@ void modeless_dialog::show(const bool allow_interaction, const unsigned /*auto_c
 
 	hide();
 
-	window_.reset(build_window());
+	build_window();
 
 	post_build(*window_);
 
@@ -66,9 +66,10 @@ void modeless_dialog::hide()
 		window_.reset(nullptr);	}
 }
 
-window* modeless_dialog::build_window() const
+void modeless_dialog::build_window()
 {
-	return build(window_id());
+	window_ = build_window_impl(window_id());
+	assert(window_);
 }
 
 void modeless_dialog::post_build(window& /*window*/)

src/gui/dialogs/modeless_dialog.hpp

@@ -14,6 +14,8 @@
 
 #pragma once
 
+#include "gui/core/window_builder.hpp"
+
 #include <memory>
 #include <string>
 
@@ -86,7 +88,7 @@ public:
 
 protected:
 	/** The window, used in show. */
-	std::unique_ptr<window> window_;
+	window_ptr_t window_;
 
 private:
 	/** The id of the window to build. */
@@ -95,12 +97,10 @@ private:
 	/**
 	 * Builds the window.
 	 *
-	 * Every dialog shows it's own kind of window, this function should return
-	 * the window to show.
-	 *
-	 * @returns                   The window to show.
+	 * Every dialog shows its own kind of window. This function handles the building
+	 * of said window. @ref window_ should be non-null after this is called.
 	 */
-	window* build_window() const;
+	void build_window();
 
 	/**
 	 * Actions to be taken directly after the window is build.

src/gui/widgets/window.hpp

@@ -63,7 +63,7 @@ class distributor;
 class window : public panel, public cursor::setter
 {
 	friend class debug_layout_graph;
-	friend window* build(const builder_window::window_resolution*);
+	friend window_ptr_t build_window_impl(const builder_window::window_resolution*);
 	friend struct window_implementation;
 	friend class invalidate_layout_blocker;
 	friend class pane;

src/scripting/lua_gui2.cpp

@@ -79,11 +79,11 @@ namespace {
 		lua_State* L;
 		scoped_dialog* prev;
 		static scoped_dialog* current;
-		std::unique_ptr<gui2::window> window;
+		gui2::window_ptr_t window;
 		typedef std::map<gui2::widget*, int> callback_map;
 		callback_map callbacks;
 
-		scoped_dialog(lua_State* l, gui2::window* w);
+		scoped_dialog(lua_State* l, gui2::window_ptr_t w);
 		~scoped_dialog();
 	private:
 		scoped_dialog(const scoped_dialog&) = delete;
@@ -91,8 +91,8 @@ namespace {
 
 	scoped_dialog* scoped_dialog::current = nullptr;
 
-	scoped_dialog::scoped_dialog(lua_State* l, gui2::window* w)
-		: L(l), prev(current), window(w), callbacks()
+	scoped_dialog::scoped_dialog(lua_State* l, gui2::window_ptr_t w)
+		: L(l), prev(current), window(std::move(w)), callbacks()
 	{
 		lua_pushstring(L, dlgclbkKey);
 		lua_createtable(L, 1, 0);
@@ -245,7 +245,7 @@ int show_dialog(lua_State* L)
 	config def_cfg = luaW_checkconfig(L, 1);
 
 	gui2::builder_window::window_resolution def(def_cfg);
-	scoped_dialog w(L, gui2::build(&def));
+	scoped_dialog w(L, gui2::build_window_impl(&def));
 
 	if(!lua_isnoneornil(L, 2)) {
 		lua_pushvalue(L, 2);