qapi: Fix error handling code on alternate conflict

The conflict check added by commit c0644771 ("qapi: Reject
alternates that can't work with keyval_parse()") doesn't work
with the following declaration:

  { 'alternate': 'Alt',
    'data': { 'one': 'bool',
              'two': 'str' } }

It crashes with:

  Traceback (most recent call last):
    File "./scripts/qapi-types.py", line 295, in <module>
      schema = QAPISchema(input_file)
    File "/home/ehabkost/rh/proj/virt/qemu/scripts/qapi.py", line 1468, in __init__
      self.exprs = check_exprs(parser.exprs)
    File "/home/ehabkost/rh/proj/virt/qemu/scripts/qapi.py", line 958, in check_exprs
      check_alternate(expr, info)
    File "/home/ehabkost/rh/proj/virt/qemu/scripts/qapi.py", line 830, in check_alternate
      % (name, key, types_seen[qtype]))
  KeyError: 'QTYPE_QSTRING'

This happens because the previously-seen conflicting member
('one') can't be found at types_seen[qtype], but at
types_seen['QTYPE_BOOL'].

Fix the bug by moving the error check to the same loop that adds
new items to types_seen, raising an exception if types_seen[qt]
is already set.

Add two additional test cases that can detect the bug.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170717180926.14924-1-ehabkost@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/scripts/qapi.py b/scripts/qapi.py
index 8aa2775f12..3693b520da 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -825,11 +825,11 @@ def check_alternate(expr, info):
             else:
                 conflicting.add('QTYPE_QNUM')
                 conflicting.add('QTYPE_QBOOL')
-        if conflicting & set(types_seen):
-            raise QAPISemError(info, "Alternate '%s' member '%s' can't "
-                               "be distinguished from member '%s'"
-                               % (name, key, types_seen[qtype]))
         for qt in conflicting:
+            if qt in types_seen:
+                raise QAPISemError(info, "Alternate '%s' member '%s' can't "
+                                   "be distinguished from member '%s'"
+                                   % (name, key, types_seen[qt]))
             types_seen[qt] = key