qapi-visit: Fix generated code when schema has forward refs

The visit_type_implicit_FOO() are generated on demand, right before
their first use.  Used by visit_type_STRUCT_fields() when STRUCT has
base FOO, and by visit_type_UNION() when flat UNION has member a FOO.

If the schema defines FOO after its first use as struct base or flat
union member, visit_type_implicit_FOO() calls
visit_type_implicit_FOO() before its definition, which doesn't
compile.

Rearrange qapi-schema-test.json to demonstrate the bug.

Fix by generating the necessary forward declaration.

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

scripts/qapi-visit.py

@@ -17,13 +17,23 @@ from qapi import *
 import re
 
 implicit_structs = []
+struct_fields_seen = set()
 
 def generate_visit_implicit_struct(type):
     global implicit_structs
     if type in implicit_structs:
         return ''
     implicit_structs.append(type)
-    return mcgen('''
+    ret = ''
+    if type not in struct_fields_seen:
+        # Need a forward declaration
+        ret += mcgen('''
+
+static void visit_type_%(c_type)s_fields(Visitor *m, %(c_type)s **obj, Error **errp);
+''',
+                     c_type=type_name(type))
+
+    ret += mcgen('''
 
 static void visit_type_implicit_%(c_type)s(Visitor *m, %(c_type)s **obj, Error **errp)
 {
@@ -38,8 +48,11 @@ static void visit_type_implicit_%(c_type)s(Visitor *m, %(c_type)s **obj, Error *
 }
 ''',
                  c_type=type_name(type))
+    return ret
 
 def generate_visit_struct_fields(name, members, base = None):
+    struct_fields_seen.add(name)
+
     ret = ''
 
     if base:

tests/qapi-schema/qapi-schema-test.json

@@ -7,13 +7,13 @@
   'data': { 'enum1': 'EnumOne', '*enum2': 'EnumOne', 'enum3': 'EnumOne', '*enum4': 'EnumOne' } }
 
 # for testing nested structs
+{ 'struct': 'UserDefOne',
+  'base': 'UserDefZero',        # intentional forward reference
+  'data': { 'string': 'str', '*enum1': 'EnumOne' } }
+
 { 'struct': 'UserDefZero',
   'data': { 'integer': 'int' } }
 
-{ 'struct': 'UserDefOne',
-  'base': 'UserDefZero',
-  'data': { 'string': 'str', '*enum1': 'EnumOne' } }
-
 { 'struct': 'UserDefTwoDictDict',
   'data': { 'userdef': 'UserDefOne', 'string': 'str' } }
 
@@ -33,29 +33,33 @@
 { 'struct': 'UserDefB',
   'data': { 'integer': 'int' } }
 
-{ 'struct': 'UserDefC',
-  'data': { 'string1': 'str', 'string2': 'str' } }
+{ 'union': 'UserDefFlatUnion',
+  'base': 'UserDefUnionBase',   # intentional forward reference
+  'discriminator': 'enum1',
+  'data': { 'value1' : 'UserDefA',
+            'value2' : 'UserDefB',
+            'value3' : 'UserDefB' } }
+# FIXME generated struct UserDefFlatUnion has members for direct base
+# UserDefOne, but lacks members for indirect base UserDefZero
 
 { 'struct': 'UserDefUnionBase',
   'data': { 'string': 'str', 'enum1': 'EnumOne' } }
 
-{ 'union': 'UserDefFlatUnion',
-  'base': 'UserDefUnionBase',
-  'discriminator': 'enum1',
-  'data': { 'value1' : 'UserDefA', 'value2' : 'UserDefB', 'value3' : 'UserDefB' } }
-# FIXME generated struct UserDefFlatUnion has members for direct base
-# UserDefOne, but lacks members for indirect base UserDefZero
-
 # this variant of UserDefFlatUnion defaults to a union that uses fields with
 # allocated types to test corner cases in the cleanup/dealloc visitor
 { 'union': 'UserDefFlatUnion2',
   'base': 'UserDefUnionBase',
   'discriminator': 'enum1',
-  'data': { 'value1' : 'UserDefC', 'value2' : 'UserDefB', 'value3' : 'UserDefA' } }
+  'data': { 'value1' : 'UserDefC', # intentional forward reference
+            'value2' : 'UserDefB',
+            'value3' : 'UserDefA' } }
 
 { 'alternate': 'UserDefAlternate',
   'data': { 'uda': 'UserDefA', 's': 'str', 'i': 'int' } }
 
+{ 'struct': 'UserDefC',
+  'data': { 'string1': 'str', 'string2': 'str' } }
+
 # for testing native lists
 { 'union': 'UserDefNativeListUnion',
   'data': { 'integer': ['int'],

tests/qapi-schema/qapi-schema-test.out

@@ -1,17 +1,17 @@
 [OrderedDict([('enum', 'EnumOne'), ('data', ['value1', 'value2', 'value3'])]),
  OrderedDict([('struct', 'NestedEnumsOne'), ('data', OrderedDict([('enum1', 'EnumOne'), ('*enum2', 'EnumOne'), ('enum3', 'EnumOne'), ('*enum4', 'EnumOne')]))]),
- OrderedDict([('struct', 'UserDefZero'), ('data', OrderedDict([('integer', 'int')]))]),
  OrderedDict([('struct', 'UserDefOne'), ('base', 'UserDefZero'), ('data', OrderedDict([('string', 'str'), ('*enum1', 'EnumOne')]))]),
+ OrderedDict([('struct', 'UserDefZero'), ('data', OrderedDict([('integer', 'int')]))]),
  OrderedDict([('struct', 'UserDefTwoDictDict'), ('data', OrderedDict([('userdef', 'UserDefOne'), ('string', 'str')]))]),
  OrderedDict([('struct', 'UserDefTwoDict'), ('data', OrderedDict([('string1', 'str'), ('dict2', 'UserDefTwoDictDict'), ('*dict3', 'UserDefTwoDictDict')]))]),
  OrderedDict([('struct', 'UserDefTwo'), ('data', OrderedDict([('string0', 'str'), ('dict1', 'UserDefTwoDict')]))]),
  OrderedDict([('struct', 'UserDefA'), ('data', OrderedDict([('boolean', 'bool')]))]),
  OrderedDict([('struct', 'UserDefB'), ('data', OrderedDict([('integer', 'int')]))]),
- OrderedDict([('struct', 'UserDefC'), ('data', OrderedDict([('string1', 'str'), ('string2', 'str')]))]),
- OrderedDict([('struct', 'UserDefUnionBase'), ('data', OrderedDict([('string', 'str'), ('enum1', 'EnumOne')]))]),
  OrderedDict([('union', 'UserDefFlatUnion'), ('base', 'UserDefUnionBase'), ('discriminator', 'enum1'), ('data', OrderedDict([('value1', 'UserDefA'), ('value2', 'UserDefB'), ('value3', 'UserDefB')]))]),
+ OrderedDict([('struct', 'UserDefUnionBase'), ('data', OrderedDict([('string', 'str'), ('enum1', 'EnumOne')]))]),
  OrderedDict([('union', 'UserDefFlatUnion2'), ('base', 'UserDefUnionBase'), ('discriminator', 'enum1'), ('data', OrderedDict([('value1', 'UserDefC'), ('value2', 'UserDefB'), ('value3', 'UserDefA')]))]),
  OrderedDict([('alternate', 'UserDefAlternate'), ('data', OrderedDict([('uda', 'UserDefA'), ('s', 'str'), ('i', 'int')]))]),
+ OrderedDict([('struct', 'UserDefC'), ('data', OrderedDict([('string1', 'str'), ('string2', 'str')]))]),
  OrderedDict([('union', 'UserDefNativeListUnion'), ('data', OrderedDict([('integer', ['int']), ('s8', ['int8']), ('s16', ['int16']), ('s32', ['int32']), ('s64', ['int64']), ('u8', ['uint8']), ('u16', ['uint16']), ('u32', ['uint32']), ('u64', ['uint64']), ('number', ['number']), ('boolean', ['bool']), ('string', ['str']), ('sizes', ['size'])]))]),
  OrderedDict([('command', 'user_def_cmd'), ('data', OrderedDict())]),
  OrderedDict([('command', 'user_def_cmd1'), ('data', OrderedDict([('ud1a', 'UserDefOne')]))]),
@@ -39,15 +39,15 @@
  {'enum_name': '__org.qemu_x-Union1Kind', 'enum_values': None},
  {'enum_name': '__org.qemu_x-AltKind', 'enum_values': None}]
 [OrderedDict([('struct', 'NestedEnumsOne'), ('data', OrderedDict([('enum1', 'EnumOne'), ('*enum2', 'EnumOne'), ('enum3', 'EnumOne'), ('*enum4', 'EnumOne')]))]),
- OrderedDict([('struct', 'UserDefZero'), ('data', OrderedDict([('integer', 'int')]))]),
  OrderedDict([('struct', 'UserDefOne'), ('base', 'UserDefZero'), ('data', OrderedDict([('string', 'str'), ('*enum1', 'EnumOne')]))]),
+ OrderedDict([('struct', 'UserDefZero'), ('data', OrderedDict([('integer', 'int')]))]),
  OrderedDict([('struct', 'UserDefTwoDictDict'), ('data', OrderedDict([('userdef', 'UserDefOne'), ('string', 'str')]))]),
  OrderedDict([('struct', 'UserDefTwoDict'), ('data', OrderedDict([('string1', 'str'), ('dict2', 'UserDefTwoDictDict'), ('*dict3', 'UserDefTwoDictDict')]))]),
  OrderedDict([('struct', 'UserDefTwo'), ('data', OrderedDict([('string0', 'str'), ('dict1', 'UserDefTwoDict')]))]),
  OrderedDict([('struct', 'UserDefA'), ('data', OrderedDict([('boolean', 'bool')]))]),
  OrderedDict([('struct', 'UserDefB'), ('data', OrderedDict([('integer', 'int')]))]),
- OrderedDict([('struct', 'UserDefC'), ('data', OrderedDict([('string1', 'str'), ('string2', 'str')]))]),
  OrderedDict([('struct', 'UserDefUnionBase'), ('data', OrderedDict([('string', 'str'), ('enum1', 'EnumOne')]))]),
+ OrderedDict([('struct', 'UserDefC'), ('data', OrderedDict([('string1', 'str'), ('string2', 'str')]))]),
  OrderedDict([('struct', 'UserDefOptions'), ('data', OrderedDict([('*i64', ['int']), ('*u64', ['uint64']), ('*u16', ['uint16']), ('*i64x', 'int'), ('*u64x', 'uint64')]))]),
  OrderedDict([('struct', 'EventStructOne'), ('data', OrderedDict([('struct1', 'UserDefOne'), ('string', 'str'), ('*enum2', 'EnumOne')]))]),
  OrderedDict([('struct', '__org.qemu_x-Base'), ('data', OrderedDict([('__org.qemu_x-member1', '__org.qemu_x-Enum')]))]),