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Re: [Qemu-devel] [PATCH v10 24/30] qapi: Factor out QAPISchemaObjectType


From: Markus Armbruster
Subject: Re: [Qemu-devel] [PATCH v10 24/30] qapi: Factor out QAPISchemaObjectType.check_clash()
Date: Tue, 10 Nov 2015 10:15:42 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

Eric Blake <address@hidden> writes:

> On 11/09/2015 07:49 AM, Markus Armbruster wrote:
>> Eric Blake <address@hidden> writes:
>> 
>>> Consolidate two common sequences of clash detection into a
>>> new QAPISchemaObjectType.check_clash() helper method.
>>>
>>> No change to generated code.
>>>
>>> Signed-off-by: Eric Blake <address@hidden>
>>>
>
>>> @@ -980,11 +980,7 @@ class QAPISchemaObjectType(QAPISchemaType):
>>>          seen = OrderedDict()
>>>          if self._base_name:
>>>              self.base = schema.lookup_type(self._base_name)
>>> -            assert isinstance(self.base, QAPISchemaObjectType)
>>> -            assert not self.base.variants       # not implemented
>>> -            self.base.check(schema)
>>> -            for m in self.base.members:
>>> -                m.check_clash(seen)
>>> +            self.base.check_clash(schema, seen)
>>>          for m in self.local_members:
>>>              m.check(schema)
>>>              m.check_clash(seen)
>>> @@ -994,6 +990,12 @@ class QAPISchemaObjectType(QAPISchemaType):
>>>              assert self.variants.tag_member in self.members
>>>              self.variants.check_clash(schema, seen)
>>>
>>> +    def check_clash(self, schema, seen):
>>> +        self.check(schema)
>> 
>> Do we want to hide this .check() inside .check_clash()?
>> 
>> QAPISchemaObjectTypeMember.check() doesn't.  I think the two better
>> behave the same.
>> 
>>> +        assert not self.variants       # not implemented
>>> +        for m in self.members:
>>> +            m.check_clash(seen)
>
> The self.check(schema) call is necessary to get self.members populated.
>  We cannot iterate over self.members if the type has not had check()
> called; this is true for both callers of type.check_clash()
> (ObjectType.check(), and Variants.check_clash()).

Yes.

We have a common protocol for QAPISchemaFOO objects, namely that certain
instance variables and methods are only valid after .check().

> You are correct that neither Member.check() nor Member.check_clash()
> call a form of type.check() - but that's because at that level, there is
> no need to populate a type.members list.
>
> On the other hand, we've been arguing that check() should populate
> everything after construction prior to anything else being run; and not
> running Variant.type.check() during Variants.check() of flat unions
> feels like we may have a hole (a flat union will have to inline its
> types to the overall JSON object, and inlining types requires access to
> type.members - but as written, we aren't populating them until
> Variants.check_clash()).  I can play with hoisting the type.check() out
> of type.check_clash() and instead keep base.check() in type.check(), and
> add variant.type.check() in Variants.check() (but only for unions, not
> for alternates), if you are interested.

My "qapi: Factor out QAPISchemaObjectTypeMember.check_clash()" added
QAPISchemaObjectTypeMember.check_clash() without changing the common
protocol.  The new QAPISchemaObjectTypeMember.check_clash() is merely a
helper for QAPISchemaObjectType.check().

Your 
Gcc: nnml:mail.redhat.xlst.qemu-devel
From: Markus Armbruster <address@hidden>
--text follows this line--
Eric Blake <address@hidden> writes:

> On 11/09/2015 07:49 AM, Markus Armbruster wrote:
>> Eric Blake <address@hidden> writes:
>> 
>>> Consolidate two common sequences of clash detection into a
>>> new QAPISchemaObjectType.check_clash() helper method.
>>>
>>> No change to generated code.
>>>
>>> Signed-off-by: Eric Blake <address@hidden>
>>>
>
>>> @@ -980,11 +980,7 @@ class QAPISchemaObjectType(QAPISchemaType):
>>>          seen = OrderedDict()
>>>          if self._base_name:
>>>              self.base = schema.lookup_type(self._base_name)
>>> -            assert isinstance(self.base, QAPISchemaObjectType)
>>> -            assert not self.base.variants       # not implemented
>>> -            self.base.check(schema)
>>> -            for m in self.base.members:
>>> -                m.check_clash(seen)
>>> +            self.base.check_clash(schema, seen)
>>>          for m in self.local_members:
>>>              m.check(schema)
>>>              m.check_clash(seen)
>>> @@ -994,6 +990,12 @@ class QAPISchemaObjectType(QAPISchemaType):
>>>              assert self.variants.tag_member in self.members
>>>              self.variants.check_clash(schema, seen)
>>>
>>> +    def check_clash(self, schema, seen):
>>> +        self.check(schema)
>> 
>> Do we want to hide this .check() inside .check_clash()?
>> 
>> QAPISchemaObjectTypeMember.check() doesn't.  I think the two better
>> behave the same.
>> 
>>> +        assert not self.variants       # not implemented
>>> +        for m in self.members:
>>> +            m.check_clash(seen)
>
> The self.check(schema) call is necessary to get self.members populated.
>  We cannot iterate over self.members if the type has not had check()
> called; this is true for both callers of type.check_clash()
> (ObjectType.check(), and Variants.check_clash()).

Yes.

We have a common protocol for QAPISchemaFOO objects, namely that certain
instance variables and methods are only valid after .check().

> You are correct that neither Member.check() nor Member.check_clash()
> call a form of type.check() - but that's because at that level, there is
> no need to populate a type.members list.
>
> On the other hand, we've been arguing that check() should populate
> everything after construction prior to anything else being run; and not
> running Variant.type.check() during Variants.check() of flat unions
> feels like we may have a hole (a flat union will have to inline its
> types to the overall JSON object, and inlining types requires access to
> type.members - but as written, we aren't populating them until
> Variants.check_clash()).  I can play with hoisting the type.check() out
> of type.check_clash() and instead keep base.check() in type.check(), and
> add variant.type.check() in Variants.check() (but only for unions, not
> for alternates), if you are interested.

My "qapi: Factor out QAPISchemaObjectTypeMember.check_clash()" adds
QAPISchemaObjectTypeMember.check_clash() without changing the common
protocol.  The new QAPISchemaObjectTypeMember.check_clash() is merely a
helper for QAPISchemaObjectType.check().

The two .check_clash() you add (one in this patch, one in the previous
one) are different: both contain calls of QAPISchemaObjectType.check().

I feel the .check() calls are too important to be buried deep like that.
I'd stick to prior practice and put the .check() calls right into
.check().  Obviously, the .check_clash() methods may only called after
.check() then, but that's nothing new.

Fixup for your previous patch:

diff --git a/scripts/qapi.py b/scripts/qapi.py
index 4c56935..357127d 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -1065,7 +1065,6 @@ class QAPISchemaObjectTypeVariants(object):
             vseen = dict(seen)
             assert isinstance(v.type, QAPISchemaObjectType)
             assert not v.type.variants       # not implemented
-            v.type.check(schema)
             for m in v.type.members:
                 m.check_clash(vseen)
 
@@ -1077,6 +1076,7 @@ class 
QAPISchemaObjectTypeVariant(QAPISchemaObjectTypeMember):
     def check(self, schema, tag_type):
         QAPISchemaObjectTypeMember.check(self, schema)
         assert self.name in tag_type.values
+        self.type.check(schema)
 
     # This function exists to support ugly simple union special cases
     # TODO get rid of them, and drop the function

This patch with conflicts resolved and the same idea worked in then
becomes:

diff --git a/scripts/qapi.py b/scripts/qapi.py
index 357127d..f443ec5 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -981,10 +981,8 @@ class QAPISchemaObjectType(QAPISchemaType):
         if self._base_name:
             self.base = schema.lookup_type(self._base_name)
             assert isinstance(self.base, QAPISchemaObjectType)
-            assert not self.base.variants       # not implemented
             self.base.check(schema)
-            for m in self.base.members:
-                m.check_clash(seen)
+            self.base.check_clash(schema, seen)
         for m in self.local_members:
             m.check(schema)
             m.check_clash(seen)
@@ -994,6 +992,11 @@ class QAPISchemaObjectType(QAPISchemaType):
             assert self.variants.tag_member in self.members
             self.variants.check_clash(schema, seen)
 
+    def check_clash(self, schema, seen):
+        assert not self.variants       # not implemented
+        for m in self.members:
+            m.check_clash(seen)
+
     def is_implicit(self):
         # See QAPISchema._make_implicit_object_type()
         return self.name[0] == ':'
@@ -1062,11 +1065,8 @@ class QAPISchemaObjectTypeVariants(object):
         for v in self.variants:
             # Reset seen map for each variant, since qapi names from one
             # branch do not affect another branch
-            vseen = dict(seen)
             assert isinstance(v.type, QAPISchemaObjectType)
-            assert not v.type.variants       # not implemented
-            for m in v.type.members:
-                m.check_clash(vseen)
+            v.type.check_clash(schema, dict(seen))
 
 
 class QAPISchemaObjectTypeVariant(QAPISchemaObjectTypeMember):

Your two check_clash() are then simple helpers, just like mine.



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