|
From: | Anton Nefedov |
Subject: | Re: [Qemu-devel] [PATCH v4 1/2] qapi: allow empty branches in flat unions |
Date: | Thu, 14 Jun 2018 12:01:21 +0300 |
User-agent: | Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 |
On 14/6/2018 10:19 AM, Markus Armbruster wrote:
Anton Nefedov <address@hidden> writes:It often happens that just a few discriminator values imply extra data in a flat union. Existing checks did not make possible to leave other values uncovered. Such cases had to be worked around by either stating a dummy (empty) type or introducing another (subset) discriminator enumeration. Both options create redundant entities in qapi files for little profit. With this patch it is not necessary anymore to add designated union fields for every possible value of a discriminator enumeration. Signed-off-by: Anton Nefedov <address@hidden> Reviewed-by: Eric Blake <address@hidden> --- docs/devel/qapi-code-gen.txt | 8 +++++--- tests/qapi-schema/flat-union-incomplete-branch.json | 9 --------- tests/qapi-schema/qapi-schema-test.json | 4 ++-- scripts/qapi/common.py | 11 ++++------- scripts/qapi/types.py | 4 +++- scripts/qapi/visit.py | 17 +++++++++++++---- tests/Makefile.include | 1 - tests/qapi-schema/flat-union-incomplete-branch.err | 1 - tests/qapi-schema/flat-union-incomplete-branch.exit | 1 - tests/qapi-schema/flat-union-incomplete-branch.out | 0 tests/qapi-schema/qapi-schema-test.out | 3 ++- 11 files changed, 29 insertions(+), 30 deletions(-) delete mode 100644 tests/qapi-schema/flat-union-incomplete-branch.json delete mode 100644 tests/qapi-schema/flat-union-incomplete-branch.err delete mode 100644 tests/qapi-schema/flat-union-incomplete-branch.exit delete mode 100644 tests/qapi-schema/flat-union-incomplete-branch.out diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt index 1366228..88a70e4 100644 --- a/docs/devel/qapi-code-gen.txt +++ b/docs/devel/qapi-code-gen.txt @@ -496,9 +496,11 @@ Resulting in these JSON objects:Notice that in a flat union, the discriminator name is controlled bythe user, but because it must map to a base member with enum type, the -code generator can ensure that branches exist for all values of the -enum (although the order of the keys need not match the declaration of -the enum). In the resulting generated C data types, a flat union is +code generator ensures that branches match the existing values of the +enum. The order of the keys need not match the declaration of the enum. +The keys need not cover all possible enum values. Omitted enum values +are still valid branches that add no additional members to the data type. +In the resulting generated C data types, a flat union is represented as a struct with the base members included directly, and then a union of structures for each branch of the struct.diff --git a/tests/qapi-schema/flat-union-incomplete-branch.json b/tests/qapi-schema/flat-union-incomplete-branch.jsondeleted file mode 100644 index 25a411b..0000000 --- a/tests/qapi-schema/flat-union-incomplete-branch.json +++ /dev/null @@ -1,9 +0,0 @@ -# we require all branches of the union to be covered -{ 'enum': 'TestEnum', - 'data': [ 'value1', 'value2' ] } -{ 'struct': 'TestTypeA', - 'data': { 'string': 'str' } } -{ 'union': 'TestUnion', - 'base': { 'type': 'TestEnum' }, - 'discriminator': 'type', - 'data': { 'value1': 'TestTypeA' } } diff --git a/tests/qapi-schema/qapi-schema-test.json b/tests/qapi-schema/qapi-schema-test.json index 46c7282..881b53b 100644 --- a/tests/qapi-schema/qapi-schema-test.json +++ b/tests/qapi-schema/qapi-schema-test.json @@ -39,7 +39,7 @@ '*enum1': 'EnumOne' } } # intentional forward reference{ 'enum': 'EnumOne',- 'data': [ 'value1', 'value2', 'value3' ] } + 'data': [ 'value1', 'value2', 'value3', 'value4' ] }{ 'struct': 'UserDefZero','data': { 'integer': 'int' } } @@ -76,7 +76,7 @@ 'discriminator': 'enum1', 'data': { 'value1' : 'UserDefA', 'value2' : 'UserDefB', - 'value3' : 'UserDefB' } } + 'value3' : 'UserDefB' } } # skip 'value4'Perhaps 'value3' : 'UserDefB' # 'value4' defaults to empty } } would be clearer.
Sure
{ 'struct': 'UserDefUnionBase','base': 'UserDefZero', diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py index 2462fc0..0f3d89b 100644 --- a/scripts/qapi/common.py +++ b/scripts/qapi/common.py @@ -779,13 +779,6 @@ def check_union(expr, info): "enum '%s'" % (key, enum_define['enum']))- # If discriminator is user-defined, ensure all values are covered- if enum_define: - for value in enum_define['data']: - if value not in members.keys(): - raise QAPISemError(info, "Union '%s' data missing '%s' branch" - % (name, value)) -def check_alternate(expr, info):name = expr['alternate'] @@ -1644,6 +1637,10 @@ class QAPISchema(object): if tag_name: variants = [self._make_variant(key, value) for (key, value) in data.items()] + # branches that are not explicitly covered get an empty type + variants += [self._make_variant(key, 'q_empty') + for key in discriminator_find_enum_define(expr)['data']Long line, flagged by pycodestyle --diff.
Done.
+ if key not in data.keys()] members = [] else: variants = [self._make_simple_variant(key, value, info)The way you desugar the union is simple enough, but it uses discriminator_find_enum_define() outside check_exprs(), which I'd rather avoid. Not something you could be reasonably expected to know. We could desugar in QAPISchemaObjectTypeVariants.check(), where we have self.tag_member.type.values. @@ -1346,10 +1346,17 @@ class QAPISchemaObjectTypeVariants(object): v.set_owner(name) def check(self, schema, seen): - if not self.tag_member: # flat union + if not self.tag_member: # flat union self.tag_member = seen[c_name(self._tag_name)] assert self._tag_name == self.tag_member.name assert isinstance(self.tag_member.type, QAPISchemaEnumType) + if self._tag_name: # flat union + cases = set([v.name for v in self.variants]) + for val in self.tag_member.type.values: + if val.name not in cases: + v = QAPISchemaObjectTypeVariant(val.name, 'q_empty') + v.set_owner(self.tag_member.owner) + self.variants.append(v) for v in self.variants: v.check(schema) # Union names must match enum values; alternate names are Not so simple anymore. Simpler: desugar in check_union(), i.e. replace your two hunks by just @@ -783,8 +783,7 @@ def check_union(expr, info): if enum_define: for value in enum_define['data']: if value not in members.keys(): - raise QAPISemError(info, "Union '%s' data missing '%s' branch" - % (name, value)) + members[value] = 'q_empty' def check_alternate(expr, info): What do you think?
it didn't feel right aesthetically to normalize by modifying the parsed expressions especially at check_exprs() stage. But maybe using discriminator_find_enum_define() is more sloppy, I can't quite see
diff --git a/scripts/qapi/types.py b/scripts/qapi/types.py index 64d9c0f..1fb2b6d 100644 --- a/scripts/qapi/types.py +++ b/scripts/qapi/types.py @@ -124,7 +124,9 @@ def gen_variants(variants): ''', c_name=c_name(variants.tag_member.name))- for var in variants.variants:+ # filter out the empty types + for var in filter(lambda var: var.type.name != 'q_empty', + variants.variants):The comment's position suggests it tells what the loop does, but that's not the case. Let's do it the old-fashioned obvious way instead: for var in variants.variants: if var.type.name == 'q_empty': continue
Done.
Aside: we need to filter out q_empty, because we don't generate a C type for it. Perhaps generating one would be simpler, but that's beyond the scope of this patch.ret += mcgen(''' %(c_type)s %(c_name)s; ''', diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py index 5d72d89..96bd32c 100644 --- a/scripts/qapi/visit.py +++ b/scripts/qapi/visit.py @@ -81,14 +81,23 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp) c_name=c_name(variants.tag_member.name))for var in variants.variants:- ret += mcgen(''' + case_str = c_enum_const(variants.tag_member.type.name, + var.name, + variants.tag_member.type.prefix) + if var.type.name == 'q_empty': + # valid variant and nothing to do + ret += mcgen(''' + case %(case)s: + break; +''', + case=case_str) + else: + ret += mcgen('''Aside: we need this, because we don't generate a visitor for q_empty.case %(case)s: visit_type_%(c_type)s_members(v, &obj->u.%(c_name)s, &err); break; ''', - case=c_enum_const(variants.tag_member.type.name, - var.name, - variants.tag_member.type.prefix), + case=case_str, c_type=var.type.c_name(), c_name=c_name(var.name))Indentation's off, flagged by pycodestyle --diff.
Done.
ret += mcgen('''diff --git a/tests/Makefile.include b/tests/Makefile.include index bb08e37..afdd0db 100644 --- a/tests/Makefile.include +++ b/tests/Makefile.include @@ -496,7 +496,6 @@ qapi-schema += flat-union-base-any.json qapi-schema += flat-union-base-union.json qapi-schema += flat-union-clash-member.json qapi-schema += flat-union-empty.json -qapi-schema += flat-union-incomplete-branch.json qapi-schema += flat-union-inline.json qapi-schema += flat-union-int-branch.json qapi-schema += flat-union-invalid-branch-key.json diff --git a/tests/qapi-schema/flat-union-incomplete-branch.err b/tests/qapi-schema/flat-union-incomplete-branch.err deleted file mode 100644 index e826bf0..0000000 --- a/tests/qapi-schema/flat-union-incomplete-branch.err +++ /dev/null @@ -1 +0,0 @@ -tests/qapi-schema/flat-union-incomplete-branch.json:6: Union 'TestUnion' data missing 'value2' branch diff --git a/tests/qapi-schema/flat-union-incomplete-branch.exit b/tests/qapi-schema/flat-union-incomplete-branch.exit deleted file mode 100644 index d00491f..0000000 --- a/tests/qapi-schema/flat-union-incomplete-branch.exit +++ /dev/null @@ -1 +0,0 @@ -1 diff --git a/tests/qapi-schema/flat-union-incomplete-branch.out b/tests/qapi-schema/flat-union-incomplete-branch.out deleted file mode 100644 index e69de29..0000000 diff --git a/tests/qapi-schema/qapi-schema-test.out b/tests/qapi-schema/qapi-schema-test.out index 542a19c..0dbcdaf 100644 --- a/tests/qapi-schema/qapi-schema-test.out +++ b/tests/qapi-schema/qapi-schema-test.out @@ -23,7 +23,7 @@ object UserDefOne base UserDefZero member string: str optional=False member enum1: EnumOne optional=True -enum EnumOne ['value1', 'value2', 'value3'] +enum EnumOne ['value1', 'value2', 'value3', 'value4'] object UserDefZero member integer: int optional=False object UserDefTwoDictDict @@ -52,6 +52,7 @@ object UserDefFlatUnion case value1: UserDefA case value2: UserDefB case value3: UserDefB + case value4: q_empty object UserDefUnionBase base UserDefZero member string: str optional=False
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