Re: [Qemu-devel] [PATCH v11 27/28] qapi: Move duplicate enum value checks to schema check()

[Markus Armbruster]

Eric Blake <address@hidden> writes:

> Similar to the previous commit, move the detection of a collision
> in enum values from parse time to QAPISchemaEnumType.check().
> This happens to also detect collisions in union branch names
> mapping to the same enum value, even when the names do not
> collide case-wise.  So for a decent error message, we have to
> determine if the enum is implicit (and if so where the real
> collision lies).
>
> Testing this showed that the test union-bad-branch wasn't adding
> much: union-clash-branches exposes the error message when branches
> directly collide, and union-max exposes the error message when
> branches cause an enum collision (union-bad-branch basically
> causes an enum collision that would not be a C collision).  This
> goes along with our desire to require ALL names to be
> case-insensitively unique.
>
> No change to generated code.
>
> Signed-off-by: Eric Blake <address@hidden>
>
> ---
> v11 (no v10): message of union-clash-branches.err changed: rely on
> enum check rather than Variant.check() to catch it
> v9: rebase to earlier changes, update commit message, break out
> helper _describe() method
> v8: rebase to earlier changes; better comments
> v7: retitle and improve commit message; earlier subclass patches
> avoid problem with detecting 'kind' collision
> v6: new patch
> ---
>  scripts/qapi.py                             | 41 
> ++++++++++++++++-------------
>  tests/Makefile                              |  1 -
>  tests/qapi-schema/enum-clash-member.err     |  2 +-
>  tests/qapi-schema/enum-max-member.err       |  2 +-
>  tests/qapi-schema/union-bad-branch.err      |  1 -
>  tests/qapi-schema/union-bad-branch.exit     |  1 -
>  tests/qapi-schema/union-bad-branch.json     |  8 ------
>  tests/qapi-schema/union-bad-branch.out      |  0
>  tests/qapi-schema/union-clash-branches.err  |  2 +-
>  tests/qapi-schema/union-clash-branches.json |  2 +-
>  tests/qapi-schema/union-max.err             |  2 +-
>  11 files changed, 28 insertions(+), 34 deletions(-)
>  delete mode 100644 tests/qapi-schema/union-bad-branch.err
>  delete mode 100644 tests/qapi-schema/union-bad-branch.exit
>  delete mode 100644 tests/qapi-schema/union-bad-branch.json
>  delete mode 100644 tests/qapi-schema/union-bad-branch.out
>
> diff --git a/scripts/qapi.py b/scripts/qapi.py
> index 1d59ce9..08a366e 100644
> --- a/scripts/qapi.py
> +++ b/scripts/qapi.py
> @@ -533,7 +533,6 @@ def check_union(expr, expr_info):
>      base = expr.get('base')
>      discriminator = expr.get('discriminator')
>      members = expr['data']
> -    values = {'MAX': '(automatic)'}
>
>      # Two types of unions, determined by discriminator.
>
> @@ -593,15 +592,6 @@ def check_union(expr, expr_info):
>                                      "enum '%s'" %
>                                      (key, enum_define["enum_name"]))
>
> -        # Otherwise, check for conflicts in the generated enum
> -        else:
> -            c_key = camel_to_upper(key)
> -            if c_key in values:
> -                raise QAPIExprError(expr_info,
> -                                    "Union '%s' member '%s' clashes with 
> '%s'"
> -                                    % (name, key, values[c_key]))
> -            values[c_key] = key
> -
>
>  def check_alternate(expr, expr_info):
>      name = expr['alternate']
> @@ -630,7 +620,6 @@ def check_enum(expr, expr_info):
>      name = expr['enum']
>      members = expr.get('data')
>      prefix = expr.get('prefix')
> -    values = {'MAX': '(automatic)'}
>
>      if not isinstance(members, list):
>          raise QAPIExprError(expr_info,
> @@ -641,12 +630,6 @@ def check_enum(expr, expr_info):
>      for member in members:
>          check_name(expr_info, "Member of enum '%s'" % name, member,
>                     enum_member=True)
> -        key = camel_to_upper(member)
> -        if key in values:
> -            raise QAPIExprError(expr_info,
> -                                "Enum '%s' member '%s' clashes with '%s'"
> -                                % (name, member, values[key]))
> -        values[key] = member
>
>
>  def check_struct(expr, expr_info):
> @@ -873,8 +856,30 @@ class QAPISchemaEnumType(QAPISchemaType):
>          self.values = values
>          self.prefix = prefix
>
> +    def _describe(self, schema):
> +        # If the enum is implicit, report the error on behalf of
> +        # the union or alternate that triggered the enum
> +        if self.is_implicit():
> +            owner = schema.lookup_type(self.name[:-4])
> +            assert owner
> +            if isinstance(owner, QAPISchemaAlternateType):
> +                return "Alternate '%s' branch" % owner.name

Didn't we just drop this kind of implicit enum?

> +            else:
> +                return "Union '%s' branch" % owner.name
> +        else:
> +            return "Enum '%s' value" % self.name

I like to call it "member" rather than value, because it avoids
confusion with the numeric value of the C enumeration constant generated
for it.

The conditional isn't exactly elegant, but it would do.  I'm not 100%
convinced we need it, though.  self.info already points to whatever
defined this enum, either an explicit enum definition, or a simple union
definition.  How do the error messages come out if we dumb down to
"Member '%s'"?

A method with a similar purpose exists in QAPISchemaObjectTypeMember,
but it's spelled describe().  It's used only from within the class.
Rename it to match this one?

> +
>      def check(self, schema):
> -        assert len(set(self.values)) == len(self.values)
> +        # Check for collisions on the generated C enum values
> +        seen = {c_enum_const(self.name, 'MAX'): '(automatic MAX)'}
> +        for value in self.values:
> +            c_value = c_enum_const(self.name, value)
> +            if c_value in seen:
> +                raise QAPIExprError(self.info,
> +                                    "%s '%s' clashes with '%s'"
> +                                    % (self._describe(schema), value,
> +                                       seen[c_value]))
> +            seen[c_value] = value

Loop body is very similar to QAPISchemaObjectTypeMember.check_clash().
Differences:

* c_enum_const(enum_name, member_name) vs. c_name(member_name).upper()

  This isn't really a difference, because the former returns the latter
  prefixed by a string that doesn't vary in the loop.

  One could argue that using c_enum_const() lets us abstract from what
  it does, but that's an illusion.  We rely on it when we generate union
  members called c_name(member_name) without checking for collisions
  again.

  By the way, c_enum_const(self.name, value, self.prefix) would be more
  correct.  Doesn't matter here, of course.

  Therefore, I'd be very much tempted to use c_name(member_name).upper()
  here as well.

* The error message.  But I suspect the same "Member '%s' clashes with
  '%s'" could do for both.

If I'm right and we can drop the differences, the common code could
become a helper function.

>
>      def is_implicit(self):
>          # See QAPISchema._make_implicit_enum_type()
> diff --git a/tests/Makefile b/tests/Makefile
> index d1c6817..cdff7a4 100644
> --- a/tests/Makefile
> +++ b/tests/Makefile
> @@ -336,7 +336,6 @@ qapi-schema += unclosed-list.json
>  qapi-schema += unclosed-object.json
>  qapi-schema += unclosed-string.json
>  qapi-schema += unicode-str.json
> -qapi-schema += union-bad-branch.json
>  qapi-schema += union-base-no-discriminator.json
>  qapi-schema += union-clash-branches.json
>  qapi-schema += union-clash-data.json
> diff --git a/tests/qapi-schema/enum-clash-member.err 
> b/tests/qapi-schema/enum-clash-member.err
> index 48bd136..84030c5 100644
> --- a/tests/qapi-schema/enum-clash-member.err
> +++ b/tests/qapi-schema/enum-clash-member.err
> @@ -1 +1 @@
> -tests/qapi-schema/enum-clash-member.json:2: Enum 'MyEnum' member 'ONE' 
> clashes with 'one'
> +tests/qapi-schema/enum-clash-member.json:2: Enum 'MyEnum' value 'ONE' 
> clashes with 'one'

Would become

   tests/qapi-schema/enum-clash-member.json:2: Member 'ONE' clashes with 'one'

Good enough for me.

> diff --git a/tests/qapi-schema/enum-max-member.err 
> b/tests/qapi-schema/enum-max-member.err
> index f77837f..6b9ef9b 100644
> --- a/tests/qapi-schema/enum-max-member.err
> +++ b/tests/qapi-schema/enum-max-member.err
> @@ -1 +1 @@
> -tests/qapi-schema/enum-max-member.json:3: Enum 'MyEnum' member 'max' clashes 
> with '(automatic)'
> +tests/qapi-schema/enum-max-member.json:3: Enum 'MyEnum' value 'max' clashes 
> with '(automatic MAX)'

   tests/qapi-schema/enum-max-member.json:3: Member 'max' clashes with 
'(automatic MAX)'

Good enough for me.

> diff --git a/tests/qapi-schema/union-bad-branch.err 
> b/tests/qapi-schema/union-bad-branch.err
> deleted file mode 100644
> index 8822735..0000000
> --- a/tests/qapi-schema/union-bad-branch.err
> +++ /dev/null
> @@ -1 +0,0 @@
> -tests/qapi-schema/union-bad-branch.json:6: Union 'MyUnion' member 'ONE' 
> clashes with 'one'
> diff --git a/tests/qapi-schema/union-bad-branch.exit 
> b/tests/qapi-schema/union-bad-branch.exit
> deleted file mode 100644
> index d00491f..0000000
> --- a/tests/qapi-schema/union-bad-branch.exit
> +++ /dev/null
> @@ -1 +0,0 @@
> -1
> diff --git a/tests/qapi-schema/union-bad-branch.json 
> b/tests/qapi-schema/union-bad-branch.json
> deleted file mode 100644
> index 913aa38..0000000
> --- a/tests/qapi-schema/union-bad-branch.json
> +++ /dev/null
> @@ -1,8 +0,0 @@
> -# we reject normal unions where branches would collide in C
> -{ 'struct': 'One',
> -  'data': { 'string': 'str' } }
> -{ 'struct': 'Two',
> -  'data': { 'number': 'int' } }
> -{ 'union': 'MyUnion',
> -  'data': { 'one': 'One',
> -            'ONE': 'Two' } }
> diff --git a/tests/qapi-schema/union-bad-branch.out 
> b/tests/qapi-schema/union-bad-branch.out
> deleted file mode 100644
> index e69de29..0000000
> diff --git a/tests/qapi-schema/union-clash-branches.err 
> b/tests/qapi-schema/union-clash-branches.err
> index 005c48d..d8f1265 100644
> --- a/tests/qapi-schema/union-clash-branches.err
> +++ b/tests/qapi-schema/union-clash-branches.err
> @@ -1 +1 @@
> -tests/qapi-schema/union-clash-branches.json:4: Union 'TestUnion' member 
> 'a_b' clashes with 'a-b'
> +tests/qapi-schema/union-clash-branches.json:4: Union 'TestUnion' branch 
> 'a_b' clashes with 'a-b'

   tests/qapi-schema/union-clash-branches.json:4: Member 'a_b' clashes with 
'a-b'

Good enough for me.

> diff --git a/tests/qapi-schema/union-clash-branches.json 
> b/tests/qapi-schema/union-clash-branches.json
> index 31d135f..3bece8c 100644
> --- a/tests/qapi-schema/union-clash-branches.json
> +++ b/tests/qapi-schema/union-clash-branches.json
> @@ -1,5 +1,5 @@
>  # Union branch name collision
>  # Reject a union that would result in a collision in generated C names (this
> -# would try to generate two enum values 'TEST_UNION_KIND_A_B').
> +# would try to generate two members 'a_b').
>  { 'union': 'TestUnion',
>    'data': { 'a-b': 'int', 'a_b': 'str' } }
> diff --git a/tests/qapi-schema/union-max.err b/tests/qapi-schema/union-max.err
> index 55ce439..b93beae 100644
> --- a/tests/qapi-schema/union-max.err
> +++ b/tests/qapi-schema/union-max.err
> @@ -1 +1 @@
> -tests/qapi-schema/union-max.json:2: Union 'Union' member 'max' clashes with 
> '(automatic)'
> +tests/qapi-schema/union-max.json:2: Union 'Union' branch 'max' clashes with 
> '(automatic MAX)'

   tests/qapi-schema/union-max.json:2: Member 'max' clashes with '(automatic 
MAX)'

Good enough for me.