Expose some weaknesses in the generator: we don't always forbid
the generation of structs that contain multiple members that map
to the same C or QMP name.  This has already been marked FIXME in
qapi.py in commit d90675fa, but having more tests will make sure
future patches produce desired behavior; and updating existing
patches to better document things doesn't hurt, either.  Some of
these collisions are already caught in the old-style parser
checks, but ultimately we want all collisions to be caught in the
new-style QAPISchema*.check() methods.

This patch focuses on C struct members, and does not consider
collisions between commands and events (affecting C function
names), or even collisions between generated C type names with
user type names (for things like automatic FOOList struct
representing array types or FOOKind for an implicit enum).

There are two types of struct collisions we want to catch:
 1) Collision between two keys in a JSON object. qapi.py prevents
    that within a single struct (see test duplicate-key), but it is
    possible to have collisions between a type's members and its
    base type's members (existing tests struct-base-clash,
    struct-base-clash-deep), and its flat union variant members
    (renamed test flat-union-clash-member).
 2) Collision between two members of the C struct that is generated
    for a given QAPI type:
    a) Multiple QAPI names map to the same C name (new test
       args-name-clash)
    b) A QAPI name maps to a C name that is used for another purpose
       (new tests flat-union-clash-branch, struct-base-clash-base,
       union-clash-data). We already fixed some such cases in commit
       0f61af3e and 1e6c1616, but more remain.
    c) Two C names generated for other purposes clash
       (updated test alternate-clash, new test union-clash-branches,
       union-clash-type, flat-union-clash-type)

Ultimately, if we need to have a flat union where a tag value
clashes with a base member name, we could change the generator to
name the union (using 'foo.u.value' rather than 'foo.value') or
otherwise munge the C name corresponding to tag values.  But
unless such a need arises, it will probably be easier to just
forbid these collisions.

Some of these negative tests will be deleted later, and positive
tests added to qapi-schema-test.json in their place, when the
generator code is reworked to avoid particular code generation
collisions in class 2).

[Note that viewing this patch with git rename detection enabled
may see some confusion due to renaming some tests while adding
others, but where the content is similar enough that git picks
the wrong pre- and post-patch files to associate]
Signed-off-by: NEric Blake <eblake@redhat.com>
Message-Id: <1443565276-4535-6-git-send-email-eblake@redhat.com>
[Improve commit message and comments a bit, drop an unrelated test]
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

Previous patches have led up to the point where I create the
new meta-type "'alternate':'Foo'".  See the previous patches
for documentation; I intentionally split as much work into
earlier patches to minimize the size of this patch, but a lot
of it is churn due to testsuite fallout after updating to the
new type.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

Previous commits demonstrated that the generator had several
flaws with less-than-perfect unions:
- a simple union that listed the same branch twice (or two variant
names that map to the same C enumerator, including the implicit
MAX sentinel) ended up generating invalid C code
- an anonymous union that listed two branches with the same qtype
ended up generating invalid C code
- the generator crashed on anonymous union attempts to use an
array type
- the generator was silently ignoring a base type for anonymous
unions
- the generator allowed unknown types or nested anonymous unions
as a branch in an anonymous union
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

Demonstrate that the qapi generator doesn't deal well with unions
that aren't up to par. Later patches will update the expected
reseults as the generator is made stricter.  A few tests work
as planned, but most show poor or missing error messages.

Of particular note, qapi-code-gen.txt documents 'base' only for
flat unions, but the tests here demonstrate that we currently allow
a 'base' to a simple union, although it is exercised only in the
testsuite.  Later patches will remove this undocumented feature, to
give us more flexibility in adding other future extensions to union
types.  For example, one possible extension is the idea of a
type-safe simple enum, where added fields tie the discriminator to
a user-defined enum type rather than creating an implicit enum from
the names in 'data'.  But adding such safety on top of a simple
enum with a base type could look ambiguous with a flat enum;
besides, the documentation also mentions how any simple union can
be represented by an equivalent flat union.  So it will be simpler
to just outlaw support for something we aren't using.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>