[gtk/wip/baedert/widget-add-style-class] widget: Add gtk_widget_add_style_class

[Timm Bäder <baedert src gnome org>]

commit 81d62f10fe3a88714ce6a284bb25aa7d25ce63ce
Author: Timm Bäder <mail baedert org>
Date:   Wed Jan 29 08:33:41 2020 +0100

    widget: Add gtk_widget_add_style_class
    
    As convenience for adding a style class to a widget's style context,
    which just adds it to the widget's css node anyway. This is a
    prerequisite for style contexts eventually going away.

 docs/reference/gtk/gtk4-sections.txt |  1 +
 gtk/gtkwidget.c                      | 20 ++++++++++++++++++++
 gtk/gtkwidget.h                      |  3 +++
 3 files changed, 24 insertions(+)
---
diff --git a/docs/reference/gtk/gtk4-sections.txt b/docs/reference/gtk/gtk4-sections.txt
index b4a737d2f0..b90d4cd75e 100644
--- a/docs/reference/gtk/gtk4-sections.txt
+++ b/docs/reference/gtk/gtk4-sections.txt
@@ -4409,6 +4409,7 @@ gtk_widget_insert_after
 gtk_widget_set_layout_manager
 gtk_widget_get_layout_manager
 gtk_widget_should_layout
+gtk_widget_add_style_class
 
 <SUBSECTION>
 gtk_widget_get_style_context
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index ba4f4b461c..6a03409017 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -13175,3 +13175,23 @@ gtk_widget_class_query_action (GtkWidgetClass      *widget_class,
 
   return FALSE;
 }
+
+/**
+ * gtk_widget_add_style_class:
+ * @widget: a #GtkWidget
+ * @style_class: The style class to add to @widget
+ *
+ * Adds @style_class to @widget. After calling this function, @widget's
+ * style will match for @style_class, after the CSS matching rules.
+ */
+void
+gtk_widget_add_style_class (GtkWidget   *widget,
+                            const char  *style_class)
+{
+  g_return_if_fail (GTK_IS_WIDGET (widget));
+  g_return_if_fail (style_class != NULL);
+  g_return_if_fail (style_class[0] != '\0');
+  g_return_if_fail (style_class[0] != '.');
+
+  gtk_style_context_add_class (gtk_widget_get_style_context (widget), style_class);
+}
diff --git a/gtk/gtkwidget.h b/gtk/gtkwidget.h
index 1719f59487..9c68e03a90 100644
--- a/gtk/gtkwidget.h
+++ b/gtk/gtkwidget.h
@@ -967,6 +967,9 @@ void                    gtk_widget_snapshot_child       (GtkWidget   *widget,
                                                          GtkSnapshot *snapshot);
 GDK_AVAILABLE_IN_ALL
 gboolean                gtk_widget_should_layout        (GtkWidget   *widget);
+GDK_AVAILABLE_IN_ALL
+void                    gtk_widget_add_style_class      (GtkWidget   *widget,
+                                                         const char  *style_class);
 
 
 /**