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qapi: allow empty branches in flat unions

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It often happens that just a few discriminator values imply extra data in
a flat union. Existing checks did not make possible to leave other values
uncovered. Such cases had to be worked around by either stating a dummy
(empty) type or introducing another (subset) discriminator enumeration.

Both options create redundant entities in qapi files for little profit.

With this patch it is not necessary anymore to add designated union
fields for every possible value of a discriminator enumeration.

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
Message-Id: <1529311206-76847-2-git-send-email-anton.nefedov@virtuozzo.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
This commit is contained in:
Anton Nefedov 2018-06-18 11:40:05 +03:00 • committed by Markus Armbruster
parent fe170d8bfa
commit 800877bb16
11 changed files with 35 additions and 30 deletions
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8
docs/devel/qapi-code-gen.txt
View file

@ -496,9 +496,11 @@ Resulting in these JSON objects:
Notice that in a flat union, the discriminator name is controlled by
the user, but because it must map to a base member with enum type, the
code generator can ensure that branches exist for all values of the
enum (although the order of the keys need not match the declaration of
the enum). In the resulting generated C data types, a flat union is
code generator ensures that branches match the existing values of the
enum. The order of the keys need not match the declaration of the enum.
The keys need not cover all possible enum values. Omitted enum values
are still valid branches that add no additional members to the data type.
In the resulting generated C data types, a flat union is
represented as a struct with the base members included directly, and
then a union of structures for each branch of the struct.