qapi: Simplify visiting of alternate types

Previously, working with alternates required two lookup arrays
and some indirection: for type Foo, we created Foo_qtypes[]
which maps each qtype to a value of the generated FooKind enum,
then look up that value in FooKind_lookup[] like we do for other
union types.

This has a couple of subtle bugs.  First, the generator was
creating a call with a parameter '(int *) &(*obj)->type' where
type is an enum type; this is unsafe if the compiler chooses
to store the enum type in a different size than int, where
assigning through the wrong size pointer can corrupt data or
cause a SIGBUS.

Related bug, not not fixed in this patch: qapi-visit.py's
gen_visit_enum() generates a cast of its enum * argument to
int *. Marked FIXME.

Second, since the values of the FooKind enum start at zero, all
entries of the Foo_qtypes[] array that were not explicitly
initialized will map to the same branch of the union as the
first member of the alternate, rather than triggering a desired
failure in visit_get_next_type().  Fortunately, the bug seldom
bites; the very next thing the input visitor does is try to
parse the incoming JSON with the wrong parser, which normally
fails; the output visitor is not used with a C struct in that
state, and the dealloc visitor has nothing to clean up (so
there is no leak).

However, the second bug IS observable in one case: parsing an
integer causes unusual behavior in an alternate that contains
at least a 'number' member but no 'int' member, because the
'number' parser accepts QTYPE_QINT in addition to the expected
QTYPE_QFLOAT (that is, since 'int' is not a member, the type
QTYPE_QINT accidentally maps to FooKind 0; if this enum value
is the 'number' branch the integer parses successfully, but if
the 'number' branch is not first, some other branch tries to
parse the integer and rejects it).  A later patch will worry
about fixing alternates to always parse all inputs that a
non-alternate 'number' would accept, for now this is still
marked FIXME in the updated test-qmp-input-visitor.c, to
merely point out that new undesired behavior of 'ans' matches
the existing undesired behavior of 'asn'.

This patch fixes the default-initialization bug by deleting the
indirection, and modifying get_next_type() to directly assign a
QTypeCode parameter.  This in turn fixes the type-casting bug,
as we are no longer casting a pointer to enum to a questionable
size. There is no longer a need to generate an implicit FooKind
enum associated with the alternate type (since the QMP wire
format never uses the stringized counterparts of the C union
member names).  Since the updated visit_get_next_type() does not
know which qtypes are expected, the generated visitor is
modified to generate an error statement if an unexpected type is
encountered.

Callers now have to know the QTYPE_* mapping when looking at the
discriminator; but so far, only the testsuite was even using the
C struct of an alternate types.  I considered the possibility of
keeping the internal enum FooKind, but initialized differently
than most generated arrays, as in:
  typedef enum FooKind {
      FOO_KIND_A = QTYPE_QDICT,
      FOO_KIND_B = QTYPE_QINT,
  } FooKind;
to create nicer aliases for knowing when to use foo->a or foo->b
when inspecting foo->type; but it turned out to add too much
complexity, especially without a client.

There is a user-visible side effect to this change, but I
consider it to be an improvement. Previously,
the invalid QMP command:
  {"execute":"blockdev-add", "arguments":{"options":
    {"driver":"raw", "id":"a", "file":true}}}
failed with:
  {"error": {"class": "GenericError",
    "desc": "Invalid parameter type for 'file', expected: QDict"}}
(visit_get_next_type() succeeded, and the error comes from the
visit_type_BlockdevOptions() expecting {}; there is no mention of
the fact that a string would also work).  Now it fails with:
  {"error": {"class": "GenericError",
    "desc": "Invalid parameter type for 'file', expected: BlockdevRef"}}
(the error when the next type doesn't match any expected types for
the overall alternate).

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1449033659-25497-5-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

4 files changed, 18 insertions, 26 deletions

diff --git a/tests/qapi-schema/alternate-empty.out b/tests/qapi-schema/alternate-empty.out
index 02b9876..f78f174 100644
--- a/tests/qapi-schema/alternate-empty.out
+++ b/tests/qapi-schema/alternate-empty.out
@@ -1,6 +1,5 @@
 object :empty
 alternate Alt
     case i: int
-enum AltKind ['i']
 enum QType ['none', 'qnull', 'qint', 'qstring', 'qdict', 'qlist', 'qfloat', 'qbool']
     prefix QTYPE
diff --git a/tests/qapi-schema/qapi-schema-test.out b/tests/qapi-schema/qapi-schema-test.out
index b87cfba..2c546b7 100644
--- a/tests/qapi-schema/qapi-schema-test.out
+++ b/tests/qapi-schema/qapi-schema-test.out
@@ -56,27 +56,21 @@ object :obj-user_def_cmd2-arg
 alternate AltIntNum
     case i: int
     case n: number
-enum AltIntNumKind ['i', 'n']
 alternate AltNumInt
     case n: number
     case i: int
-enum AltNumIntKind ['n', 'i']
 alternate AltNumStr
     case n: number
     case s: str
-enum AltNumStrKind ['n', 's']
 alternate AltStrBool
     case s: str
     case b: bool
-enum AltStrBoolKind ['s', 'b']
 alternate AltStrInt
     case s: str
     case i: int
-enum AltStrIntKind ['s', 'i']
 alternate AltStrNum
     case s: str
     case n: number
-enum AltStrNumKind ['s', 'n']
 event EVENT_A None
 event EVENT_B None
 event EVENT_C :obj-EVENT_C-arg
@@ -114,7 +108,6 @@ alternate UserDefAlternate
     case uda: UserDefA
     case s: str
     case i: int
-enum UserDefAlternateKind ['uda', 's', 'i']
 object UserDefB
     member intb: int optional=False
     member a-b: bool optional=True
@@ -180,7 +173,6 @@ event __ORG.QEMU_X-EVENT __org.qemu_x-Struct
 alternate __org.qemu_x-Alt
     case __org.qemu_x-branch: str
     case b: __org.qemu_x-Base
-enum __org.qemu_x-AltKind ['__org.qemu_x-branch', 'b']
 object __org.qemu_x-Base
     member __org.qemu_x-member1: __org.qemu_x-Enum optional=False
 enum __org.qemu_x-Enum ['__org.qemu_x-value']
diff --git a/tests/test-qmp-input-visitor.c b/tests/test-qmp-input-visitor.c
index d48ebdd..43b9e18 100644
--- a/tests/test-qmp-input-visitor.c
+++ b/tests/test-qmp-input-visitor.c
@@ -312,13 +312,13 @@ static void test_visitor_in_alternate(TestInputVisitorData *data,
 
     v = visitor_input_test_init(data, "42");
     visit_type_UserDefAlternate(v, &tmp, NULL, &error_abort);
-    g_assert_cmpint(tmp->type, ==, USER_DEF_ALTERNATE_KIND_I);
+    g_assert_cmpint(tmp->type, ==, QTYPE_QINT);
     g_assert_cmpint(tmp->u.i, ==, 42);
     qapi_free_UserDefAlternate(tmp);
 
     v = visitor_input_test_init(data, "'string'");
     visit_type_UserDefAlternate(v, &tmp, NULL, &error_abort);
-    g_assert_cmpint(tmp->type, ==, USER_DEF_ALTERNATE_KIND_S);
+    g_assert_cmpint(tmp->type, ==, QTYPE_QSTRING);
     g_assert_cmpstr(tmp->u.s, ==, "string");
     qapi_free_UserDefAlternate(tmp);
 
@@ -347,36 +347,37 @@ static void test_visitor_in_alternate_number(TestInputVisitorData *data,
     error_free_or_abort(&err);
     qapi_free_AltStrBool(asb);
 
-    /* FIXME: Order of alternate should not affect semantics; asn should
-     * parse the same as ans */
+    /* FIXME: integer should parse as number */
     v = visitor_input_test_init(data, "42");
     visit_type_AltStrNum(v, &asn, NULL, &err);
-    /* FIXME g_assert_cmpint(asn->type, == ALT_STR_NUM_KIND_N); */
+    /* FIXME g_assert_cmpint(asn->type, ==, QTYPE_QFLOAT); */
     /* FIXME g_assert_cmpfloat(asn->u.n, ==, 42); */
     error_free_or_abort(&err);
     qapi_free_AltStrNum(asn);
 
+    /* FIXME: integer should parse as number */
     v = visitor_input_test_init(data, "42");
-    visit_type_AltNumStr(v, &ans, NULL, &error_abort);
-    g_assert_cmpint(ans->type, ==, ALT_NUM_STR_KIND_N);
-    g_assert_cmpfloat(ans->u.n, ==, 42);
+    visit_type_AltNumStr(v, &ans, NULL, &err);
+    /* FIXME g_assert_cmpint(ans->type, ==, QTYPE_QFLOAT); */
+    /* FIXME g_assert_cmpfloat(ans->u.n, ==, 42); */
+    error_free_or_abort(&err);
     qapi_free_AltNumStr(ans);
 
     v = visitor_input_test_init(data, "42");
     visit_type_AltStrInt(v, &asi, NULL, &error_abort);
-    g_assert_cmpint(asi->type, ==, ALT_STR_INT_KIND_I);
+    g_assert_cmpint(asi->type, ==, QTYPE_QINT);
     g_assert_cmpint(asi->u.i, ==, 42);
     qapi_free_AltStrInt(asi);
 
     v = visitor_input_test_init(data, "42");
     visit_type_AltIntNum(v, &ain, NULL, &error_abort);
-    g_assert_cmpint(ain->type, ==, ALT_INT_NUM_KIND_I);
+    g_assert_cmpint(ain->type, ==, QTYPE_QINT);
     g_assert_cmpint(ain->u.i, ==, 42);
     qapi_free_AltIntNum(ain);
 
     v = visitor_input_test_init(data, "42");
     visit_type_AltNumInt(v, &ani, NULL, &error_abort);
-    g_assert_cmpint(ani->type, ==, ALT_NUM_INT_KIND_I);
+    g_assert_cmpint(ani->type, ==, QTYPE_QINT);
     g_assert_cmpint(ani->u.i, ==, 42);
     qapi_free_AltNumInt(ani);
 
@@ -389,13 +390,13 @@ static void test_visitor_in_alternate_number(TestInputVisitorData *data,
 
     v = visitor_input_test_init(data, "42.5");
     visit_type_AltStrNum(v, &asn, NULL, &error_abort);
-    g_assert_cmpint(asn->type, ==, ALT_STR_NUM_KIND_N);
+    g_assert_cmpint(asn->type, ==, QTYPE_QFLOAT);
     g_assert_cmpfloat(asn->u.n, ==, 42.5);
     qapi_free_AltStrNum(asn);
 
     v = visitor_input_test_init(data, "42.5");
     visit_type_AltNumStr(v, &ans, NULL, &error_abort);
-    g_assert_cmpint(ans->type, ==, ALT_NUM_STR_KIND_N);
+    g_assert_cmpint(ans->type, ==, QTYPE_QFLOAT);
     g_assert_cmpfloat(ans->u.n, ==, 42.5);
     qapi_free_AltNumStr(ans);
 
@@ -406,13 +407,13 @@ static void test_visitor_in_alternate_number(TestInputVisitorData *data,
 
     v = visitor_input_test_init(data, "42.5");
     visit_type_AltIntNum(v, &ain, NULL, &error_abort);
-    g_assert_cmpint(ain->type, ==, ALT_INT_NUM_KIND_N);
+    g_assert_cmpint(ain->type, ==, QTYPE_QFLOAT);
     g_assert_cmpfloat(ain->u.n, ==, 42.5);
     qapi_free_AltIntNum(ain);
 
     v = visitor_input_test_init(data, "42.5");
     visit_type_AltNumInt(v, &ani, NULL, &error_abort);
-    g_assert_cmpint(ani->type, ==, ALT_NUM_INT_KIND_N);
+    g_assert_cmpint(ani->type, ==, QTYPE_QFLOAT);
     g_assert_cmpfloat(ani->u.n, ==, 42.5);
     qapi_free_AltNumInt(ani);
 }
diff --git a/tests/test-qmp-output-visitor.c b/tests/test-qmp-output-visitor.c
index 4196e66..3078442 100644
--- a/tests/test-qmp-output-visitor.c
+++ b/tests/test-qmp-output-visitor.c
@@ -428,7 +428,7 @@ static void test_visitor_out_alternate(TestOutputVisitorData *data,
     UserDefAlternate *tmp;
 
     tmp = g_new0(UserDefAlternate, 1);
-    tmp->type = USER_DEF_ALTERNATE_KIND_I;
+    tmp->type = QTYPE_QINT;
     tmp->u.i = 42;
 
     visit_type_UserDefAlternate(data->ov, &tmp, NULL, &error_abort);
@@ -441,7 +441,7 @@ static void test_visitor_out_alternate(TestOutputVisitorData *data,
     qobject_decref(arg);
 
     tmp = g_new0(UserDefAlternate, 1);
-    tmp->type = USER_DEF_ALTERNATE_KIND_S;
+    tmp->type = QTYPE_QSTRING;
     tmp->u.s = g_strdup("hello");
 
     visit_type_UserDefAlternate(data->ov, &tmp, NULL, &error_abort);