qapi: Forbid 'any' inside an alternate

The whole point of an alternate is to allow some type-safety while
still accepting more than one JSON type.  Meanwhile, the 'any'
type exists to bypass type-safety altogether.  The two are
incompatible: you can't accept every type, and still tell which
branch of the alternate to use for the parse; fix this to give a
sane error instead of a Python stack trace.

Note that other types that can't be alternate members are caught
earlier, by check_type().

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1455778109-6278-4-git-send-email-eblake@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi.py

@@ -629,7 +629,10 @@ def check_alternate(expr, expr_info):
                    value,
                    allow_metas=['built-in', 'union', 'struct', 'enum'])
         qtype = find_alternate_member_qtype(value)
-        assert qtype
+        if not qtype:
+            raise QAPIExprError(expr_info,
+                                "Alternate '%s' member '%s' cannot use "
+                                "type '%s'" % (name, key, value))
         if qtype in types_seen:
             raise QAPIExprError(expr_info,
                                 "Alternate '%s' member '%s' can't "

tests/Makefile

@@ -241,6 +241,7 @@ check-qtest-xtensaeb-y = $(check-qtest-xtensa-y)
 
 check-qtest-generic-y += tests/qom-test$(EXESUF)
 
+qapi-schema += alternate-any.json
 qapi-schema += alternate-array.json
 qapi-schema += alternate-base.json
 qapi-schema += alternate-clash.json

tests/qapi-schema/alternate-any.err

@@ -0,0 +1 @@
+tests/qapi-schema/alternate-any.json:2: Alternate 'Alt' member 'one' cannot use type 'any'

tests/qapi-schema/alternate-any.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/alternate-any.json

@@ -0,0 +1,4 @@
+# we do not allow the 'any' type as an alternate branch
+{ 'alternate': 'Alt',
+  'data': { 'one': 'any',
+            'two': 'int' } }