[gedit/gnome-41] tab: backport text-cut-off bug fix

[Sébastien Wilmet <swilmet src gnome org>]

commit 48a44f35391457ce04edd5aa6777d2dffcb109a9
Author: Sébastien Wilmet <swilmet informatique-libre be>
Date:   Wed Jul 27 11:40:53 2022 +0200

    tab: backport text-cut-off bug fix
    
    Cherry-picking the commits from master were not possible.
    So it's a backport.
    
    For relevant commits on master:
    commit 5adfe2c8b
    commit 21ae0bab6
    commit be6c7695d
    commit 0476a1d44
    
    See https://gitlab.gnome.org/GNOME/gedit/-/issues/42

 gedit/gedit-tab.c | 120 ++++++++++++++++++++++++++++++++++++------------------
 1 file changed, 80 insertions(+), 40 deletions(-)
---
diff --git a/gedit/gedit-tab.c b/gedit/gedit-tab.c
index d305f8d7e..f7ca7fe11 100644
--- a/gedit/gedit-tab.c
+++ b/gedit/gedit-tab.c
@@ -60,7 +60,8 @@ struct _GeditTab
 
        GtkSourceFileSaverFlags save_flags;
 
-       guint idle_scroll;
+       guint scroll_timeout;
+       guint scroll_idle;
 
        gint auto_save_interval;
        guint auto_save_timeout;
@@ -333,10 +334,16 @@ gedit_tab_dispose (GObject *object)
 
        remove_auto_save_timeout (tab);
 
-       if (tab->idle_scroll != 0)
+       if (tab->scroll_timeout != 0)
        {
-               g_source_remove (tab->idle_scroll);
-               tab->idle_scroll = 0;
+               g_source_remove (tab->scroll_timeout);
+               tab->scroll_timeout = 0;
+       }
+
+       if (tab->scroll_idle != 0)
+       {
+               g_source_remove (tab->scroll_idle);
+               tab->scroll_idle = 0;
        }
 
        if (tab->cancellable != NULL)
@@ -1040,14 +1047,36 @@ should_show_progress_info (GTimer  **timer,
 }
 
 static gboolean
-scroll_to_cursor (GeditTab *tab)
+scroll_timeout_cb (GeditTab *tab)
 {
        GeditView *view;
 
        view = gedit_tab_get_view (tab);
        gedit_view_scroll_to_cursor (view);
 
-       tab->idle_scroll = 0;
+       tab->scroll_timeout = 0;
+       return G_SOURCE_REMOVE;
+}
+
+static gboolean
+scroll_idle_cb (GeditTab *tab)
+{
+       /* The idle is not enough, for a detailed analysis of this, see:
+        * https://wiki.gnome.org/Apps/Gedit/FixingTextCutOffBug
+        * or the commit message that changed this.
+        * (here it's a hack, a proper solution in GTK/GtkTextView should be
+        * found).
+        */
+       if (tab->scroll_timeout == 0)
+       {
+               /* Same number of ms as GtkSearchEntry::search-changed delay.
+                * Small enough to not be noticeable, but needs to be at least a
+                * few frames from the GdkFrameClock (during app startup).
+                */
+               tab->scroll_timeout = g_timeout_add (150, (GSourceFunc)scroll_timeout_cb, tab);
+       }
+
+       tab->scroll_idle = 0;
        return G_SOURCE_REMOVE;
 }
 
@@ -1641,48 +1670,68 @@ goto_line (GTask *loading_task)
 {
        LoaderData *data = g_task_get_task_data (loading_task);
        GeditDocument *doc = gedit_tab_get_document (data->tab);
+       gboolean check_is_cursor_position = FALSE;
        GtkTextIter iter;
 
-       /* Move the cursor at the requested line if any. */
+       /* To the top by default. */
+       gtk_text_buffer_get_start_iter (GTK_TEXT_BUFFER (doc), &iter);
+
+       /* At the requested line/column if set. */
        if (data->line_pos > 0)
        {
-               gedit_document_goto_line_offset (doc,
-                                                data->line_pos - 1,
-                                                MAX (0, data->column_pos - 1));
-               return;
+               gtk_text_buffer_get_iter_at_line_offset (GTK_TEXT_BUFFER (doc),
+                                                        &iter,
+                                                        data->line_pos - 1,
+                                                        MAX (0, data->column_pos - 1));
+               check_is_cursor_position = TRUE;
        }
 
-       /* If enabled, move to the position stored in the metadata. */
-       if (g_settings_get_boolean (data->tab->editor_settings, GEDIT_SETTINGS_RESTORE_CURSOR_POSITION))
+       /* From metadata. */
+       else if (g_settings_get_boolean (data->tab->editor_settings,
+                                        GEDIT_SETTINGS_RESTORE_CURSOR_POSITION))
        {
-               gchar *pos;
-               gint offset;
-
-               pos = gedit_document_get_metadata (doc, GEDIT_METADATA_ATTRIBUTE_POSITION);
-
-               offset = pos != NULL ? atoi (pos) : 0;
-               g_free (pos);
+               gchar *position_str;
+               guint64 offset = 0;
 
-               gtk_text_buffer_get_iter_at_offset (GTK_TEXT_BUFFER (doc),
-                                                   &iter,
-                                                   MAX (0, offset));
+               position_str = gedit_document_get_metadata (doc, GEDIT_METADATA_ATTRIBUTE_POSITION);
 
-               /* make sure it's a valid position, if the file
-                * changed we may have ended up in the middle of
-                * a utf8 character cluster */
-               if (!gtk_text_iter_is_cursor_position (&iter))
+               if (position_str != NULL &&
+                   g_ascii_string_to_unsigned (position_str,
+                                               10,
+                                               0,
+                                               G_MAXINT,
+                                               &offset,
+                                               NULL))
                {
-                       gtk_text_iter_set_line_offset (&iter, 0);
+                       gtk_text_buffer_get_iter_at_offset (GTK_TEXT_BUFFER (doc),
+                                                           &iter,
+                                                           (gint) offset);
+                       check_is_cursor_position = TRUE;
                }
+
+               g_free (position_str);
        }
 
-       /* Otherwise to the top. */
-       else
+       /* Make sure it's a valid position, to not end up in the middle of a
+        * utf8 character cluster.
+        */
+       if (check_is_cursor_position &&
+           !gtk_text_iter_is_cursor_position (&iter))
        {
-               gtk_text_buffer_get_start_iter (GTK_TEXT_BUFFER (doc), &iter);
+               gtk_text_iter_set_line_offset (&iter, 0);
        }
 
        gtk_text_buffer_place_cursor (GTK_TEXT_BUFFER (doc), &iter);
+
+       /* Scroll to the cursor when the document is loaded, we need to do it in
+        * an idle as after the document is loaded the textview is still
+        * redrawing and relocating its internals.
+        */
+       if (data->tab->scroll_idle == 0 &&
+           !gtk_text_iter_is_start (&iter))
+       {
+               data->tab->scroll_idle = g_idle_add ((GSourceFunc)scroll_idle_cb, data->tab);
+       }
 }
 
 static gboolean
@@ -1747,15 +1796,6 @@ successful_load (GTask *loading_task)
 
        goto_line (loading_task);
 
-       /* Scroll to the cursor when the document is loaded, we need to do it in
-        * an idle as after the document is loaded the textview is still
-        * redrawing and relocating its internals.
-        */
-       if (data->tab->idle_scroll == 0)
-       {
-               data->tab->idle_scroll = g_idle_add ((GSourceFunc)scroll_to_cursor, data->tab);
-       }
-
        location = gtk_source_file_loader_get_location (data->loader);
 
        /* If the document is readonly we don't care how many times the file