Hi

On Fri, May 21, 2021 at 3:58 PM Markus Armbruster <armbru@redhat.com> wrote:

> marcandre.lureau@redhat.com writes:
>
> > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> >
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > Tested-by: John Snow <jsnow@redhat.com>
> > ---
> >  docs/devel/qapi-code-gen.txt | 27 ++++++++++++++++-----------
> >  1 file changed, 16 insertions(+), 11 deletions(-)
> >
> > diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt
> > index edaaf7ec40..4a3fd02723 100644
> > --- a/docs/devel/qapi-code-gen.txt
> > +++ b/docs/devel/qapi-code-gen.txt
> > @@ -780,26 +780,31 @@ downstream command __com.redhat_drive-mirror.
> >  === Configuring the schema ===
> >
> >  Syntax:
> > -    COND = STRING
> > -         | [ STRING, ... ]
> > +    COND = CFG-ID
> > +         | [ COND, ... ]
> > +         | { 'all: [ COND, ... ] }
> > +         | { 'any: [ COND, ... ] }
> > +         | { 'not': COND }
> >
> > -All definitions take an optional 'if' member.  Its value must be a
> > -string or a list of strings.  A string is shorthand for a list
> > -containing just that string.  The code generated for the definition
> > -will then be guarded by #if STRING for each STRING in the COND list.
> > +    CFG-ID = STRING
> > +
> > +All definitions take an optional 'if' member. Its value must be a
> string, a list
> > +of strings or an object with a single member 'all', 'any' or 'not'. A
> string is
> > +shorthand for a list containing just that string. A list is a shorthand
> for a
> > +'all'-member object. The C code generated for the definition will then
> be guarded
>
> Please try to make your changes blend into the existing text: limit line
> length to 70 characters, and put two spaces between sentences.
>

ok


> I doubt the CFG-ID non-terminal is useful.  Elsewhere, we do without,
> e.g. ENUM-VALUE, ALTERNATIVE, FEATURE.
>
> Sure the [ COND, ... ] sugar is worth the bother?
>

Maybe not


> Perhaps
>
>        COND = STRING
>             | { 'all: [ COND, ... ] }
>             | { 'any: [ COND, ... ] }
>             | { 'not': COND }
>
>    All definitions take an optional 'if' member.  The form STRING is
>    shorthand for { 'any': [ STRING ] }.  The C code generated ...
>

ok


> > +by an #if precessor expression generated from that condition: 'all':
> [COND, ...]
> > +will generate '(COND && ...)', 'any': [COND, ...] '(COND || ...)',
> 'not': COND '!COND'.
>
> The technical term is "#if preprocessing directive".  Let's use it.
>

ok


> I find the last part unnecessarily hard to read.  What about:
>
>    ... generated from that condition:
>
>    * { 'all': [COND, ...] } will generate #if (COND && ...)
>    * { 'any': [COND, ...] } will generate #if (COND || ...)
>    * { 'not': COND } will generate #if !COND
>
>
Yes!

>
> >  Example: a conditional struct
> >
> >   { 'struct': 'IfStruct', 'data': { 'foo': 'int' },
> > -   'if': ['CONFIG_FOO', 'HAVE_BAR'] }
> > +   'if': { 'all': [ 'CONFIG_FOO', 'HAVE_BAR' ] } }
> >
> >  gets its generated code guarded like this:
> >
> > - #if defined(CONFIG_FOO)
> > - #if defined(HAVE_BAR)
> > + #if defined(CONFIG_FOO) && defined(HAVE_BAR)
> >   ... generated code ...
> > - #endif /* defined(HAVE_BAR) */
> > - #endif /* defined(CONFIG_FOO) */
> > + #endif /* defined(HAVE_BAR) && defined(CONFIG_FOO) */
> >
> >  Individual members of complex types, commands arguments, and
> >  event-specific data can also be made conditional.  This requires the
>
>
>
thanks

-- 
Marc-André Lureau