xmleditor: make gtksourceview optional

The only thing that GtkSourceView gives us is syntax highlighting and
auto-indent. When this library is not available, we can still offer xml
editing with a plain textview with very little lost functionality.

Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>

virt-manager.spec

@@ -25,9 +25,6 @@ Requires: libvirt-glib >= 0.0.9
 Requires: gtk-vnc2
 Requires: spice-gtk3
 
-# We can work with gtksourceview 3 or gtksourceview4, pick the latest one
-Requires: gtksourceview4
-
 # virt-manager is one of those apps that people will often install onto
 # a headless machine for use over SSH. This means the virt-manager dep
 # chain needs to provide everything we need to get a usable app experience.
@@ -42,6 +39,10 @@ Requires: dconf
 # no ambiguity.
 Requires: vte291
 
+# We can use GtkTextView, gtksourceview 3 or gtksourceview4, recommend
+# the latest one but don't make it a hard requirement
+Recommends: gtksourceview4
+
 # Weak dependencies for the common virt-manager usecase
 Recommends: (libvirt-daemon-kvm or libvirt-daemon-qemu)
 Recommends: libvirt-daemon-config-network

virtManager/xmleditor.py

@@ -7,13 +7,24 @@ import gi
 from virtinst import log
 
 # We can use either gtksourceview3 or gtksourceview4
+have_gtksourceview = True
 try:
     gi.require_version("GtkSource", "4")
     log.debug("Using GtkSource 4")
 except ValueError:  # pragma: no cover
-    gi.require_version("GtkSource", "3.0")
-    log.debug("Using GtkSource 3.0")
-from gi.repository import GtkSource
+    try:
+        gi.require_version("GtkSource", "3.0")
+        log.debug("Using GtkSource 3.0")
+    except ValueError:
+        log.debug("Not using GtkSource")
+        have_gtksourceview = False
+
+if have_gtksourceview:
+    from gi.repository import GtkSource
+else:
+    # if GtkSourceView is not available, just use a plain TextView. This will
+    # only disable auto-indent and syntax highlighting.
+    from gi.repository import Gtk
 
 from .lib import uiutil
 from .baseclass import vmmGObjectUI
@@ -66,17 +77,20 @@ class vmmXMLEditor(vmmGObjectUI):
                 not enabled)
 
     def _init_ui(self):
-        self._srcview = GtkSource.View()
-        self._srcbuff = self._srcview.get_buffer()
-
-        lang = GtkSource.LanguageManager.get_default().get_language("xml")
-        self._srcbuff.set_language(lang)
+        if have_gtksourceview:
+            self._srcview = GtkSource.View()
+            self._srcbuff = self._srcview.get_buffer()
+            self._srcview.set_auto_indent(True)
+            lang = GtkSource.LanguageManager.get_default().get_language("xml")
+            self._srcbuff.set_language(lang)
+            self._srcbuff.set_highlight_syntax(True)
+        else:
+            self._srcview = Gtk.TextView()
+            self._srcbuff = self._srcview.get_buffer()
 
         self._srcview.set_monospace(True)
-        self._srcview.set_auto_indent(True)
         self._srcview.get_accessible().set_name("XML editor")
 
-        self._srcbuff.set_highlight_syntax(True)
         self._srcbuff.connect("changed", self._buffer_changed_cb)
 
         self.widget("xml-notebook").connect("switch-page",