qapi: Whitelist commands that don't return dictionary

...or an array of dictionaries.  Although we have to cater to
existing commands, returning a non-dictionary means the command
is not extensible (no new name/value pairs can be added if more
information must be returned in parallel).  By making the
whitelist explicit, any new command that falls foul of this
practice will have to be self-documenting, which will encourage
developers to either justify the action or rework the design to
use a dictionary after all.

It's a little bit sloppy that we share a single whitelist among
three clients (it's too permissive for each).  If this is a
problem, a future patch could tighten things by having the
generator take the whitelist as an argument (as in
scripts/qapi-commands.py --legacy-returns=...), or by having
the generator output C code that requires explicit use of the
whitelist (as in:
 #ifndef FROBNICATE_LEGACY_RETURN_OK
 # error Command 'frobnicate' should return a dictionary
 #endif
then having the callers define appropriate macros).  But until
we need such fine-grained separation (if ever), this patch does
the job just fine.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

11 files changed, 37 insertions, 20 deletions

diff --git a/scripts/qapi.py b/scripts/qapi.py
index 5bc32e311d..2402d053e4 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -32,6 +32,30 @@ builtin_types = {
     'size':     'QTYPE_QINT',
 }
 
+# Whitelist of commands allowed to return a non-dictionary
+returns_whitelist = [
+    # From QMP:
+    'human-monitor-command',
+    'query-migrate-cache-size',
+    'query-tpm-models',
+    'query-tpm-types',
+    'ringbuf-read',
+
+    # From QGA:
+    'guest-file-open',
+    'guest-fsfreeze-freeze',
+    'guest-fsfreeze-freeze-list',
+    'guest-fsfreeze-status',
+    'guest-fsfreeze-thaw',
+    'guest-get-time',
+    'guest-set-vcpus',
+    'guest-sync',
+    'guest-sync-delimited',
+
+    # From qapi-schema-test:
+    'user_def_cmd3',
+]
+
 enum_types = []
 struct_types = []
 union_types = []
@@ -354,11 +378,12 @@ def check_command(expr, expr_info):
     check_type(expr_info, "'data' for command '%s'" % name,
                expr.get('data'), allow_dict=True, allow_optional=True,
                allow_metas=['union', 'struct'])
+    returns_meta = ['union', 'struct']
+    if name in returns_whitelist:
+        returns_meta += ['built-in', 'alternate', 'enum']
     check_type(expr_info, "'returns' for command '%s'" % name,
                expr.get('returns'), allow_array=True, allow_dict=True,
-               allow_optional=True,
-               allow_metas=['built-in', 'union', 'alternate', 'struct',
-                            'enum'])
+               allow_optional=True, allow_metas=returns_meta)
 
 def check_event(expr, expr_info):
     global events
diff --git a/tests/qapi-schema/returns-alternate.err b/tests/qapi-schema/returns-alternate.err
index e69de29bb2..dfbb419cac 100644
--- a/tests/qapi-schema/returns-alternate.err
+++ b/tests/qapi-schema/returns-alternate.err
@@ -0,0 +1 @@
+tests/qapi-schema/returns-alternate.json:3: 'returns' for command 'oops' cannot use alternate type 'Alt'
diff --git a/tests/qapi-schema/returns-alternate.exit b/tests/qapi-schema/returns-alternate.exit
index 573541ac97..d00491fd7e 100644
--- a/tests/qapi-schema/returns-alternate.exit
+++ b/tests/qapi-schema/returns-alternate.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/returns-alternate.json b/tests/qapi-schema/returns-alternate.json
index b3b91fd3d4..972390c06b 100644
--- a/tests/qapi-schema/returns-alternate.json
+++ b/tests/qapi-schema/returns-alternate.json
@@ -1,3 +1,3 @@
-# FIXME: we should reject returns if it is an alternate type
+# we reject returns if it is an alternate type
 { 'alternate': 'Alt', 'data': { 'a': 'int', 'b': 'str' } }
 { 'command': 'oops', 'returns': 'Alt' }
diff --git a/tests/qapi-schema/returns-alternate.out b/tests/qapi-schema/returns-alternate.out
index 8a03ed3adf..e69de29bb2 100644
--- a/tests/qapi-schema/returns-alternate.out
+++ b/tests/qapi-schema/returns-alternate.out
@@ -1,4 +0,0 @@
-[OrderedDict([('alternate', 'Alt'), ('data', OrderedDict([('a', 'int'), ('b', 'str')]))]),
- OrderedDict([('command', 'oops'), ('returns', 'Alt')])]
-[{'enum_name': 'AltKind', 'enum_values': None}]
-[]
diff --git a/tests/qapi-schema/returns-int.json b/tests/qapi-schema/returns-int.json
index 7888fb1b08..870ec6366b 100644
--- a/tests/qapi-schema/returns-int.json
+++ b/tests/qapi-schema/returns-int.json
@@ -1,2 +1,3 @@
 # It is okay (although not extensible) to return a non-dictionary
-{ 'command': 'okay', 'returns': 'int' }
+# But to make it work, the name must be in a whitelist
+{ 'command': 'guest-get-time', 'returns': 'int' }
diff --git a/tests/qapi-schema/returns-int.out b/tests/qapi-schema/returns-int.out
index 36b00a9f3b..70b3ac5e6f 100644
--- a/tests/qapi-schema/returns-int.out
+++ b/tests/qapi-schema/returns-int.out
@@ -1,3 +1,3 @@
-[OrderedDict([('command', 'okay'), ('returns', 'int')])]
+[OrderedDict([('command', 'guest-get-time'), ('returns', 'int')])]
 []
 []
diff --git a/tests/qapi-schema/returns-whitelist.err b/tests/qapi-schema/returns-whitelist.err
index e69de29bb2..a41f019a52 100644
--- a/tests/qapi-schema/returns-whitelist.err
+++ b/tests/qapi-schema/returns-whitelist.err
@@ -0,0 +1 @@
+tests/qapi-schema/returns-whitelist.json:10: 'returns' for command 'no-way-this-will-get-whitelisted' cannot use built-in type 'array of int'
diff --git a/tests/qapi-schema/returns-whitelist.exit b/tests/qapi-schema/returns-whitelist.exit
index 573541ac97..d00491fd7e 100644
--- a/tests/qapi-schema/returns-whitelist.exit
+++ b/tests/qapi-schema/returns-whitelist.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/returns-whitelist.json b/tests/qapi-schema/returns-whitelist.json
index 8328563b4e..e8b3cea396 100644
--- a/tests/qapi-schema/returns-whitelist.json
+++ b/tests/qapi-schema/returns-whitelist.json
@@ -1,4 +1,4 @@
-# FIXME: we should enforce that 'returns' be a dict or array of dict unless whitelisted
+# we enforce that 'returns' be a dict or array of dict unless whitelisted
 { 'command': 'human-monitor-command',
   'data': {'command-line': 'str', '*cpu-index': 'int'},
   'returns': 'str' }
diff --git a/tests/qapi-schema/returns-whitelist.out b/tests/qapi-schema/returns-whitelist.out
index 2adcd8ba10..e69de29bb2 100644
--- a/tests/qapi-schema/returns-whitelist.out
+++ b/tests/qapi-schema/returns-whitelist.out
@@ -1,7 +0,0 @@
-[OrderedDict([('command', 'human-monitor-command'), ('data', OrderedDict([('command-line', 'str'), ('*cpu-index', 'int')])), ('returns', 'str')]),
- OrderedDict([('enum', 'TpmModel'), ('data', ['tpm-tis'])]),
- OrderedDict([('command', 'query-tpm-models'), ('returns', ['TpmModel'])]),
- OrderedDict([('command', 'guest-get-time'), ('returns', 'int')]),
- OrderedDict([('command', 'no-way-this-will-get-whitelisted'), ('returns', ['int'])])]
-[{'enum_name': 'TpmModel', 'enum_values': ['tpm-tis']}]
-[]