Move check_if() from check_keys() to check_exprs() and call it later,
so its error messages gain an "in definition" line.
Checking values in a function named check_keys() is unclean anyway.
The original sin was commit 0545f6b887 "qapi: Better error messages
for bad expressions", which checks the value of key 'name'. More
sinning in commit 2cbf09925a "qapi: More rigorous checking for type
safety bypass", commit c818408e44 "qapi: Implement boxed types for
commands/events", and commit 967c885108 "qapi: add 'if' to top-level
expressions". This commit does penance for the latter. The next
commits will do penance for the others.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190927134639.4284-19-armbru@redhat.com>
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