qapi: add 'if' to top-level expressions

Accept 'if' key in top-level elements, accepted as string or list of
string type. The following patches will modify the test visitor to
check the value is correctly saved, and generate #if/#endif code (as a
single #if/endif line or a series for a list).

Example of 'if' key:
{ 'struct': 'TestIfStruct', 'data': { 'foo': 'int' },
  'if': 'defined(TEST_IF_STRUCT)' }

The generated code is for now *unconditional*. Later patches generate
the conditionals.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180703155648.11933-2-marcandre.lureau@redhat.com>
[Commit message and Documentation improved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/tests/test-qmp-cmds.c b/tests/test-qmp-cmds.c
index 491b0c4..840530b 100644
--- a/tests/test-qmp-cmds.c
+++ b/tests/test-qmp-cmds.c
@@ -12,6 +12,18 @@
 
 static QmpCommandList qmp_commands;
 
+/* #if defined(TEST_IF_STRUCT) && defined(TEST_IF_CMD) */
+UserDefThree *qmp_TestIfCmd(TestIfStruct *foo, Error **errp)
+{
+    return NULL;
+}
+/* #endif */
+
+UserDefThree *qmp_TestCmdReturnDefThree(Error **errp)
+{
+    return NULL;
+}
+
 void qmp_user_def_cmd(Error **errp)
 {
 }