Re: [PATCH 1/9] qapi: New special feature flag "unstable"

[John Snow <jsnow@redhat.com>]

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On Mon, Oct 25, 2021 at 1:26 AM Markus Armbruster <armbru@redhat.com> wrote:

> By convention, names starting with "x-" are experimental.  The parts
> of external interfaces so named may be withdrawn or changed
> incompatibly in future releases.
>
> Drawback: promoting something from experimental to stable involves a
> name change.  Client code needs to be updated.
>
> Moreover, the convention is not universally observed:
>
> * QOM type "input-barrier" has properties "x-origin", "y-origin".
>   Looks accidental, but it's ABI since 4.2.
>
> * QOM types "memory-backend-file", "memory-backend-memfd",
>   "memory-backend-ram", and "memory-backend-epc" have a property
>   "x-use-canonical-path-for-ramblock-id" that is documented to be
>   stable despite its name.
>
> We could document these exceptions, but documentation helps only
> humans.  We want to recognize "unstable" in code, like "deprecated".
>
> Replace the convention by a new special feature flag "unstable".  It
> will be recognized by the QAPI generator, like the existing feature
> flag "deprecated", and unlike regular feature flags.
>
> This commit updates documentation and prepares tests.  The next commit
> updates the QAPI schema.  The remaining patches update the QAPI
> generator and wire up -compat policy checking.
>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>  docs/devel/qapi-code-gen.rst            | 9 ++++++---
>  tests/qapi-schema/qapi-schema-test.json | 7 +++++--
>  tests/qapi-schema/qapi-schema-test.out  | 5 +++++
>  3 files changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/docs/devel/qapi-code-gen.rst b/docs/devel/qapi-code-gen.rst
> index 4071c9074a..38f2d7aad3 100644
> --- a/docs/devel/qapi-code-gen.rst
> +++ b/docs/devel/qapi-code-gen.rst
> @@ -713,6 +713,10 @@ member as deprecated.  It is not supported elsewhere
> so far.
>  Interfaces so marked may be withdrawn in future releases in accordance
>  with QEMU's deprecation policy.
>
> +Feature "unstable" marks a command, event, enum value, or struct
> +member as unstable.  It is not supported elsewhere so far.  Interfaces
> +so marked may be withdrawn or changed incompatibly in future releases.
> +
>
>  Naming rules and reserved names
>  -------------------------------
> @@ -746,9 +750,8 @@ Member name ``u`` and names starting with ``has-`` or
> ``has_`` are reserved
>  for the generator, which uses them for unions and for tracking
>  optional members.
>
> -Any name (command, event, type, member, or enum value) beginning with
> -``x-`` is marked experimental, and may be withdrawn or changed
> -incompatibly in a future release.
> +Names beginning with ``x-`` used to signify "experimental".  This
> +convention has been replaced by special feature "unstable".
>
>  Pragmas ``command-name-exceptions`` and ``member-name-exceptions`` let
>  you violate naming rules.  Use for new code is strongly discouraged. See
> diff --git a/tests/qapi-schema/qapi-schema-test.json
> b/tests/qapi-schema/qapi-schema-test.json
> index b677ab861d..43b8697002 100644
> --- a/tests/qapi-schema/qapi-schema-test.json
> +++ b/tests/qapi-schema/qapi-schema-test.json
> @@ -273,7 +273,7 @@
>    'data': { 'foo': { 'type': 'int', 'features': [ 'deprecated' ] } },
>    'features': [ 'feature1' ] }
>  { 'struct': 'FeatureStruct2',
> -  'data': { 'foo': 'int' },
> +  'data': { 'foo': { 'type': 'int', 'features': [ 'unstable' ] } },
>    'features': [ { 'name': 'feature1' } ] }
>  { 'struct': 'FeatureStruct3',
>    'data': { 'foo': 'int' },
> @@ -331,7 +331,7 @@
>  { 'command': 'test-command-features1',
>    'features': [ 'deprecated' ] }
>  { 'command': 'test-command-features3',
> -  'features': [ 'feature1', 'feature2' ] }
> +  'features': [ 'unstable', 'feature1', 'feature2' ] }
>
>  { 'command': 'test-command-cond-features1',
>    'features': [ { 'name': 'feature1', 'if': 'TEST_IF_FEATURE_1'} ] }
> @@ -348,3 +348,6 @@
>
>  { 'event': 'TEST_EVENT_FEATURES1',
>    'features': [ 'deprecated' ] }
> +
> +{ 'event': 'TEST_EVENT_FEATURES2',
> +  'features': [ 'unstable' ] }
> diff --git a/tests/qapi-schema/qapi-schema-test.out
> b/tests/qapi-schema/qapi-schema-test.out
> index 16846dbeb8..1f9585fa9b 100644
> --- a/tests/qapi-schema/qapi-schema-test.out
> +++ b/tests/qapi-schema/qapi-schema-test.out
> @@ -308,6 +308,7 @@ object FeatureStruct1
>      feature feature1
>  object FeatureStruct2
>      member foo: int optional=False
> +        feature unstable
>      feature feature1
>  object FeatureStruct3
>      member foo: int optional=False
> @@ -373,6 +374,7 @@ command test-command-features1 None -> None
>      feature deprecated
>  command test-command-features3 None -> None
>      gen=True success_response=True boxed=False oob=False preconfig=False
> +    feature unstable
>      feature feature1
>      feature feature2
>  command test-command-cond-features1 None -> None
> @@ -394,6 +396,9 @@ event TEST_EVENT_FEATURES0 FeatureStruct1
>  event TEST_EVENT_FEATURES1 None
>      boxed=False
>      feature deprecated
> +event TEST_EVENT_FEATURES2 None
> +    boxed=False
> +    feature unstable
>  module include/sub-module.json
>  include sub-sub-module.json
>  object SecondArrayRef
> --
> 2.31.1
>
>
Feels odd to combine the doc update *and* test prep, but eh, whatever.

Reviewed-by: John Snow <jsnow@redhat.com>

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