[PATCH 4/9] qapi: Tools for sets of special feature flags in generated code

[John Snow]

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

> New enum QapiSpecialFeature enumerates the special feature flags.
>
> New helper gen_special_features() returns code to represent a
> collection of special feature flags as a bitset.
>
> The next few commits will put them to use.
>
> Signed-off-by: Markus Armbruster <armbru at redhat.com>
> ---
>  include/qapi/util.h    |  4 ++++
>  scripts/qapi/gen.py    | 13 +++++++++++++
>  scripts/qapi/schema.py |  3 +++
>  3 files changed, 20 insertions(+)
>
> diff --git a/include/qapi/util.h b/include/qapi/util.h
> index 257c600f99..7a8d5c7d72 100644
> --- a/include/qapi/util.h
> +++ b/include/qapi/util.h
> @@ -11,6 +11,10 @@
>  #ifndef QAPI_UTIL_H
>  #define QAPI_UTIL_H
>
> +typedef enum {
> +    QAPI_DEPRECATED,
> +} QapiSpecialFeature;
> +
>  /* QEnumLookup flags */
>  #define QAPI_ENUM_DEPRECATED 1
>
> diff --git a/scripts/qapi/gen.py b/scripts/qapi/gen.py
> index 2ec1e7b3b6..9d07b88cf6 100644
> --- a/scripts/qapi/gen.py
> +++ b/scripts/qapi/gen.py
> @@ -29,6 +29,7 @@
>      mcgen,
>  )
>  from .schema import (
> +    QAPISchemaFeature,
>      QAPISchemaIfCond,
>      QAPISchemaModule,
>      QAPISchemaObjectType,
> @@ -37,6 +38,18 @@
>  from .source import QAPISourceInfo
>
>
> +def gen_special_features(features: QAPISchemaFeature):
> +    ret = ''
> +    sep = ''
> +
> +    for feat in features:
> +        if feat.is_special():
> +            ret += ('%s1u << QAPI_%s' % (sep, feat.name.upper()))
>

Building the constant name here "feels" fragile, but I'll trust that the
test suite and/or the compiler will catch us if we accidentally goof up
this mapping. In the interest of simplicity, then, "sure, why not."


> +            sep = ' | '
> +
>
+    return ret or '0'
> +
>

Subjectively more pythonic:

special_features = [f"1u << QAPI_{feat.name.upper()}" for feat in features
if feat.is_special()]
ret = ' | '.join(special_features)
return ret or '0'

A bit more dense, but more functional. Up to you, but I find join() easier
to read and reason about for the presence of separators.


> +
>  class QAPIGen:
>      def __init__(self, fname: str):
>          self.fname = fname
> diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
> index 6d5f46509a..55f82d7389 100644
> --- a/scripts/qapi/schema.py
> +++ b/scripts/qapi/schema.py
> @@ -725,6 +725,9 @@ def connect_doc(self, doc):
>  class QAPISchemaFeature(QAPISchemaMember):
>      role = 'feature'
>
> +    def is_special(self):
> +        return self.name in ('deprecated')
> +
>

alrighty.

(Briefly wondered: is it worth naming special features as a property of the
class, but with only two names, it's probably fine enough to leave it
embedded in the method logic. Only a style thing and doesn't have any
actual impact that I can imagine, so ... nevermind.)


>
>  class QAPISchemaObjectTypeMember(QAPISchemaMember):
>      def __init__(self, name, info, typ, optional, ifcond=None,
> features=None):
> --
> 2.31.1
>
>
Well, either way:

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