[vte] lib: Add getter support for smart pointer

[Christian Persch <chpe src gnome org>]

commit bd5025524bf9ca3490ba3739312618a1f7092766
Author: Christian Persch <chpe src gnome org>
Date:   Thu Oct 22 20:34:51 2020 +0200

    lib: Add getter support for smart pointer

 src/std-glue.hh | 43 +++++++++++++++++++++++++++++++++++++++++++
 src/vte.cc      | 17 +++++++++--------
 src/widget.cc   | 10 +++++-----
 3 files changed, 57 insertions(+), 13 deletions(-)
---
diff --git a/src/std-glue.hh b/src/std-glue.hh
index 2a35b6a2..946f023f 100644
--- a/src/std-glue.hh
+++ b/src/std-glue.hh
@@ -18,6 +18,7 @@
 #pragma once
 
 #include <memory>
+#include <type_traits>
 
 namespace vte {
 
@@ -36,4 +37,46 @@ class FreeableDeleter<T> { \
 public: inline void operator()(T* t) { func(t); } \
 }
 
+template<typename S, typename V, V default_v = 0>
+class ValueGetter {
+public:
+        explicit ValueGetter(S& storage,
+                             V default_vv = default_v) noexcept
+                : m_storage{storage},
+                  m_value{default_vv}
+        {
+        }
+
+        ~ValueGetter()
+        {
+                if constexpr (std::is_nothrow_assignable_v<S&, V>) {
+                        m_storage = m_value;
+                } else {
+                        m_storage.reset(m_value);
+                }
+        }
+
+        ValueGetter(ValueGetter const&) = delete;
+        ValueGetter(ValueGetter&&) = delete;
+
+        ValueGetter& operator=(ValueGetter const&) = delete;
+        ValueGetter& operator=(ValueGetter&&) = delete;
+
+        operator V*() noexcept { return &m_value; }
+        V* operator&() noexcept { return &m_value; }
+
+private:
+        S& m_storage;
+        V m_value;
+};
+
+template<typename S, typename V, V default_v = 0>
+auto get_value(S& s) { return vte::ValueGetter<S, V, default_v>{s}; }
+
+template<typename T>
+using FreeableGetter = ValueGetter<Freeable<T>, T*, nullptr>;
+
+template<typename T>
+auto get_freeable(vte::Freeable<T>& freeable) { return vte::FreeableGetter<T>{freeable}; }
+
 } // namespace vte
diff --git a/src/vte.cc b/src/vte.cc
index ddf5a251..aa29348f 100644
--- a/src/vte.cc
+++ b/src/vte.cc
@@ -7235,22 +7235,23 @@ Terminal::update_font()
 bool
 Terminal::set_font_desc(PangoFontDescription const* font_desc)
 {
-       /* Create an owned font description. */
-        PangoFontDescription *desc;
+        auto desc = vte::Freeable<PangoFontDescription>{};
 
         auto context = gtk_widget_get_style_context(m_widget);
         gtk_style_context_save(context);
         gtk_style_context_set_state (context, GTK_STATE_FLAG_NORMAL);
-        gtk_style_context_get(context, GTK_STATE_FLAG_NORMAL, "font", &desc, nullptr);
+        gtk_style_context_get(context, GTK_STATE_FLAG_NORMAL, "font",
+                              &vte::get_freeable(desc),
+                              nullptr);
         gtk_style_context_restore(context);
 
-       pango_font_description_set_family_static (desc, "monospace");
+       pango_font_description_set_family_static(desc.get(), "monospace");
        if (font_desc != nullptr) {
-               pango_font_description_merge (desc, font_desc, TRUE);
+               pango_font_description_merge(desc.get(), font_desc, TRUE);
                _VTE_DEBUG_IF(VTE_DEBUG_MISC) {
                        if (desc) {
                                char *tmp;
-                               tmp = pango_font_description_to_string(desc);
+                               tmp = pango_font_description_to_string(desc.get());
                                g_printerr("Using pango font \"%s\".\n", tmp);
                                g_free (tmp);
                        }
@@ -7261,7 +7262,7 @@ Terminal::set_font_desc(PangoFontDescription const* font_desc)
        }
 
         bool const same_desc = m_unscaled_font_desc &&
-                pango_font_description_equal(m_unscaled_font_desc.get(), desc);
+                pango_font_description_equal(m_unscaled_font_desc.get(), desc.get());
 
        /* Note that we proceed to recreating the font even if the description
         * are the same.  This is because maybe screen
@@ -7269,7 +7270,7 @@ Terminal::set_font_desc(PangoFontDescription const* font_desc)
         * detected at font creation time and respected.
         */
 
-        m_unscaled_font_desc.reset(desc); /* adopts */
+        m_unscaled_font_desc = std::move(desc);
         update_font();
 
         return !same_desc;
diff --git a/src/widget.cc b/src/widget.cc
index 9e7c16ec..31061413 100644
--- a/src/widget.cc
+++ b/src/widget.cc
@@ -349,17 +349,17 @@ void
 Widget::im_preedit_changed() noexcept
 {
         char* str = nullptr;
-       PangoAttrList* attrs = nullptr;
        int cursorpos = 0;
 
-        gtk_im_context_get_preedit_string(m_im_context.get(), &str, &attrs, &cursorpos);
+        auto attrs = vte::Freeable<PangoAttrList>{};
+        gtk_im_context_get_preedit_string(m_im_context.get(), &str,
+                                          vte::get_freeable(attrs),
+                                          &cursorpos);
         _vte_debug_print(VTE_DEBUG_EVENTS, "Input method pre-edit changed (%s,%d).\n",
                          str, cursorpos);
 
         if (str != nullptr)
-                m_terminal->im_preedit_changed(str, cursorpos, vte::take_freeable(attrs));
-        else
-                pango_attr_list_unref(attrs);
+                m_terminal->im_preedit_changed(str, cursorpos, std::move(attrs));
 
         g_free(str);
 }