Re: [Qemu-devel] [PATCH RFC v2 25/47] qapi: Make generators work on sorted schema expressions

[Markus Armbruster]

Eric Blake <address@hidden> writes:

> On 07/01/2015 02:22 PM, Markus Armbruster wrote:
>> Order of expressions doesn't matter.  QAPISchema().get_exprs() returns
>> expressions in the order they're parsed.
>> 
>> I'm going to refactor this code.  To check refactorings, I want to
>> diff the generated code, and for that I need to preserve its order.
>> 
>> Since I don't feel like preserving parse order, I'm changing
>> get_expr() to return the expressions sorted by name.  This order will
>> be trivial to preserve.  It also makes the generated code slightly
>> easier to navigate.
>
> Huge change to the generated files, but that's to be expected.  Diffstat
> shows it is not a straight 1:1 reshuffle:
>
>  qapi-event.c                          |  890 +--
>  qapi-event.h                          |  190
>  qapi-types.c                          | 1996 +++----
>  qapi-types.h                          | 5420 ++++++++++----------
>  qapi-visit.c                          | 9088 
> +++++++++++++++++-----------------
>  qapi-visit.h                          |  746 +-
>  qga/qapi-generated/qga-qapi-types.c   |  148
>  qga/qapi-generated/qga-qapi-types.h   |  340 -
>  qga/qapi-generated/qga-qapi-visit.c   |  446 -
>  qga/qapi-generated/qga-qapi-visit.h   |   54
>  qga/qapi-generated/qga-qmp-commands.h |   38
>  qga/qapi-generated/qga-qmp-marshal.c  |  864 +--
>  qmp-commands.h                        |  376 -
>  13 files changed, 10308 insertions(+), 10288 deletions(-)
>
> but that's probably because you now emit forward declarations for things
> that occur alphabetically after their first use (since 8/47 in this
> series touched forward declarations), whereas before they happened to
> occurr in topological order from the parse.

Here's my cheap trick for sanity checking this commit: compare before
and after *sorted*.  Results:

* qapi-event.h
  - Members of enum QAPIEvent reordered, values changed accordingly (but
    they shouldn't matter)

* qapi-visit.c
  - A bunch of new forward declarations

* test-qapi-visit.c
  - One forward declaration gone.

>> Signed-off-by: Markus Armbruster <address@hidden>
>> ---
>>  scripts/qapi.py | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
>> 
>> diff --git a/scripts/qapi.py b/scripts/qapi.py
>> index cac7ab5..20ffdaf 100644
>> --- a/scripts/qapi.py
>> +++ b/scripts/qapi.py
>> @@ -1017,7 +1017,14 @@ class QAPISchema(object):
>>          self.check()
>>  
>>      def get_exprs(self):
>> -        return [expr_elem['expr'] for expr_elem in self.exprs]
>> +        def expr_name(expr):
>> +            name = expr.get('enum') or expr.get('union') \
>> +                   or expr.get('alternate') or expr.get('struct') \
>> +                   or expr.get('command') or expr.get('event')
>> +            assert name
>> +            return name
>
> When I was working on this file earlier, I half toyed with the idea of
> adding expr_elem['name'] holding the entity name, and expr_elem['meta']
> holding what meta-type the entity represents; it might have made some of
> our later 6-way switches simpler.  But with your hierarchy of actual
> objects, I'm not sure my idea helps any more.

The more work we do with the new internal representation instead of the
syntax tree, the less it'll help.

>> +        return sorted([expr_elem['expr'] for expr_elem in self.exprs],
>> +                      key=expr_name)
>
> Python has some nice compact syntactical gems - I'd hate the amount of
> boilerplate required to write this same filter using straight C code :)
>
> Reviewed-by: Eric Blake <address@hidden>

Thanks!