qapi: Add tests for empty unions

The documentation claims that alternates are useful for
allowing two or more types, although nothing enforces this.
Meanwhile, it is silent on whether empty unions are allowed.
In practice, the generated code will compile, in part because
we have a 'void *data' branch; but attempting to visit such a
type will cause an abort().  While there's no technical reason
that a degenerate union could not be made to work, it's harder
to justify the time spent in chasing known (the current
abort() during visit) and unknown corner cases, than it would
be to just outlaw them.  A future patch will probably take the
approach of forbidding them; in the meantime, we can at least
add testsuite coverage to make it obvious where things stand.

In addition to adding tests to expose the problems, we also
need to adjust existing tests that are meant to test something
else, but which could fail for the wrong reason if we reject
degenerate alternates/unions.

Note that empty structs are explicitly supported (for example,
right now they are the only way to specify that one branch of a
flat union adds no additional members), and empty enums are
covered by the testsuite as working (even if they do not seem
to have much use).

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1443565276-4535-8-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

15 files changed, 30 insertions, 2 deletions

diff --git a/tests/Makefile b/tests/Makefile
index 49fdbe28aa..209eca9bae 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -229,6 +229,7 @@ qapi-schema += alternate-base.json
 qapi-schema += alternate-clash.json
 qapi-schema += alternate-conflict-dict.json
 qapi-schema += alternate-conflict-string.json
+qapi-schema += alternate-empty.json
 qapi-schema += alternate-good.json
 qapi-schema += alternate-nested.json
 qapi-schema += alternate-unknown.json
@@ -280,6 +281,7 @@ qapi-schema += flat-union-base-union.json
 qapi-schema += flat-union-clash-branch.json
 qapi-schema += flat-union-clash-member.json
 qapi-schema += flat-union-clash-type.json
+qapi-schema += flat-union-empty.json
 qapi-schema += flat-union-inline.json
 qapi-schema += flat-union-int-branch.json
 qapi-schema += flat-union-invalid-branch-key.json
@@ -338,6 +340,7 @@ qapi-schema += union-base-no-discriminator.json
 qapi-schema += union-clash-branches.json
 qapi-schema += union-clash-data.json
 qapi-schema += union-clash-type.json
+qapi-schema += union-empty.json
 qapi-schema += union-invalid-base.json
 qapi-schema += union-max.json
 qapi-schema += union-optional-branch.json
diff --git a/tests/qapi-schema/alternate-empty.err b/tests/qapi-schema/alternate-empty.err
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/qapi-schema/alternate-empty.err
diff --git a/tests/qapi-schema/alternate-empty.exit b/tests/qapi-schema/alternate-empty.exit
new file mode 100644
index 0000000000..573541ac97
--- /dev/null
+++ b/tests/qapi-schema/alternate-empty.exit
@@ -0,0 +1 @@
+0
diff --git a/tests/qapi-schema/alternate-empty.json b/tests/qapi-schema/alternate-empty.json
new file mode 100644
index 0000000000..db3820f841
--- /dev/null
+++ b/tests/qapi-schema/alternate-empty.json
@@ -0,0 +1,2 @@
+# FIXME - alternates should list at least two types to be useful
+{ 'alternate': 'Alt', 'data': { 'i': 'int' } }
diff --git a/tests/qapi-schema/alternate-empty.out b/tests/qapi-schema/alternate-empty.out
new file mode 100644
index 0000000000..0f153b6f60
--- /dev/null
+++ b/tests/qapi-schema/alternate-empty.out
@@ -0,0 +1,4 @@
+object :empty
+alternate Alt
+    case i: int
+enum AltKind ['i']
diff --git a/tests/qapi-schema/alternate-nested.json b/tests/qapi-schema/alternate-nested.json
index c4233b9f33..8e22186491 100644
--- a/tests/qapi-schema/alternate-nested.json
+++ b/tests/qapi-schema/alternate-nested.json
@@ -2,4 +2,4 @@
 { 'alternate': 'Alt1',
   'data': { 'name': 'str', 'value': 'int' } }
 { 'alternate': 'Alt2',
-  'data': { 'nested': 'Alt1' } }
+  'data': { 'nested': 'Alt1', 'b': 'bool' } }
diff --git a/tests/qapi-schema/alternate-unknown.json b/tests/qapi-schema/alternate-unknown.json
index ad5c103028..08c80dced0 100644
--- a/tests/qapi-schema/alternate-unknown.json
+++ b/tests/qapi-schema/alternate-unknown.json
@@ -1,3 +1,3 @@
 # we reject an alternate with unknown type in branch
 { 'alternate': 'Alt',
-  'data': { 'unknown': 'MissingType' } }
+  'data': { 'unknown': 'MissingType', 'i': 'int' } }
diff --git a/tests/qapi-schema/flat-union-empty.err b/tests/qapi-schema/flat-union-empty.err
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/qapi-schema/flat-union-empty.err
diff --git a/tests/qapi-schema/flat-union-empty.exit b/tests/qapi-schema/flat-union-empty.exit
new file mode 100644
index 0000000000..573541ac97
--- /dev/null
+++ b/tests/qapi-schema/flat-union-empty.exit
@@ -0,0 +1 @@
+0
diff --git a/tests/qapi-schema/flat-union-empty.json b/tests/qapi-schema/flat-union-empty.json
new file mode 100644
index 0000000000..67dd2978eb
--- /dev/null
+++ b/tests/qapi-schema/flat-union-empty.json
@@ -0,0 +1,4 @@
+# FIXME - flat unions should not be empty
+{ 'enum': 'Empty', 'data': [ ] }
+{ 'struct': 'Base', 'data': { 'type': 'Empty' } }
+{ 'union': 'Union', 'base': 'Base', 'discriminator': 'type', 'data': { } }
diff --git a/tests/qapi-schema/flat-union-empty.out b/tests/qapi-schema/flat-union-empty.out
new file mode 100644
index 0000000000..0e0665af3b
--- /dev/null
+++ b/tests/qapi-schema/flat-union-empty.out
@@ -0,0 +1,7 @@
+object :empty
+object Base
+    member type: Empty optional=False
+enum Empty []
+object Union
+    base Base
+    tag type
diff --git a/tests/qapi-schema/union-empty.err b/tests/qapi-schema/union-empty.err
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/qapi-schema/union-empty.err
diff --git a/tests/qapi-schema/union-empty.exit b/tests/qapi-schema/union-empty.exit
new file mode 100644
index 0000000000..573541ac97
--- /dev/null
+++ b/tests/qapi-schema/union-empty.exit
@@ -0,0 +1 @@
+0
diff --git a/tests/qapi-schema/union-empty.json b/tests/qapi-schema/union-empty.json
new file mode 100644
index 0000000000..1785007113
--- /dev/null
+++ b/tests/qapi-schema/union-empty.json
@@ -0,0 +1,2 @@
+# FIXME - unions should not be empty
+{ 'union': 'Union', 'data': { } }
diff --git a/tests/qapi-schema/union-empty.out b/tests/qapi-schema/union-empty.out
new file mode 100644
index 0000000000..8b5a7bf585
--- /dev/null
+++ b/tests/qapi-schema/union-empty.out
@@ -0,0 +1,3 @@
+object :empty
+object Union
+enum UnionKind []