[RFC QEMU PATCH] ui: Make the DisplayType enum entries conditional

[Thomas Huth <thuth@redhat.com>]

Libvirt's "domcapabilities" command has a way to state whether
certain graphic frontends are available in QEMU or not. Originally,
libvirt looked at the "--help" output of the QEMU binary to determine
whether SDL was available or not (by looking for the "-sdl" parameter
in the help text), but since libvirt stopped doing this analysis of
the help text, the detection of SDL is currently broken, see:

 https://bugzilla.redhat.com/show_bug.cgi?id=1790902

QEMU should provide a way via the QMP interface instead. The simplest
way, without introducing additional commands, is to make the DisplayType
enum entries conditional, so that the enum only contains the entries if
the corresponding CONFIG_xxx switches have been set. Unfortunately, this
only works for sdl, cocoa and spice, since gtk, egl-headless and curses
are hard-wired in the "data" section of the DisplayOptions, and thus
unfortunately always have to be defined.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 qapi/ui.json | 12 +++++++++---
 ui/console.c |  4 ++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/qapi/ui.json b/qapi/ui.json
index 1052ca9c38..c4f44cfe50 100644
--- a/qapi/ui.json
+++ b/qapi/ui.json
@@ -1126,9 +1126,15 @@
 #
 ##
 { 'enum'    : 'DisplayType',
-  'data'    : [ 'default', 'none', 'gtk', 'sdl',
-                'egl-headless', 'curses', 'cocoa',
-                'spice-app'] }
+  'data'    : [
+    { 'name': 'default' },
+    { 'name': 'none' },
+    { 'name': 'gtk' },
+    { 'name': 'sdl', 'if': 'defined(CONFIG_SDL)' },
+    { 'name': 'egl-headless' },
+    { 'name': 'curses' },
+    { 'name': 'cocoa', 'if': 'defined(CONFIG_COCOA)' },
+    { 'name': 'spice-app', 'if': 'defined(CONFIG_SPICE)'} ] }
 
 ##
 # @DisplayOptions:
diff --git a/ui/console.c b/ui/console.c
index 2de5f4105b..954f7162c3 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -2371,8 +2371,12 @@ bool qemu_display_find_default(DisplayOptions *opts)
 {
     static DisplayType prio[] = {
         DISPLAY_TYPE_GTK,
+#if defined(CONFIG_SDL)
         DISPLAY_TYPE_SDL,
+#endif
+#if defined(CONFIG_COCOA)
         DISPLAY_TYPE_COCOA
+#endif
     };
     int i;
 
-- 
2.27.0