qapi: add 'if' to top-level expressions

Accept 'if' key in top-level elements, accepted as string or list of
string type. The following patches will modify the test visitor to
check the value is correctly saved, and generate #if/#endif code (as a
single #if/endif line or a series for a list).

Example of 'if' key:
{ 'struct': 'TestIfStruct', 'data': { 'foo': 'int' },
  'if': 'defined(TEST_IF_STRUCT)' }

The generated code is for now *unconditional*. Later patches generate
the conditionals.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180703155648.11933-2-marcandre.lureau@redhat.com>
[Commit message and Documentation improved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

docs/devel/qapi-code-gen.txt

@@ -744,6 +744,35 @@ Example: Red Hat, Inc. controls redhat.com, and may therefore add a
 downstream command __com.redhat_drive-mirror.
 
 
+=== Configuring the schema ===
+
+The 'struct', 'enum', 'union', 'alternate', 'command' and 'event'
+top-level expressions can take an 'if' key.  Its value must be a string
+or a list of strings.  A string is shorthand for a list containing just
+that string.  The code generated for the top-level expression will then
+be guarded by #if COND for each COND in the list.
+
+Example: a conditional struct
+
+ { 'struct': 'IfStruct', 'data': { 'foo': 'int' },
+   'if': ['defined(CONFIG_FOO)', 'defined(HAVE_BAR)'] }
+
+gets its generated code guarded like this:
+
+ #if defined(CONFIG_FOO)
+ #if defined(HAVE_BAR)
+ ... generated code ...
+ #endif /* defined(HAVE_BAR) */
+ #endif /* defined(CONFIG_FOO) */
+
+Please note that you are responsible to ensure that the C code will
+compile with an arbitrary combination of conditions, since the
+generators are unable to check it at this point.
+
+The presence of 'if' keys in the schema is reflected through to the
+introspection output depending on the build configuration.
+
+
 == Client JSON Protocol introspection ==
 
 Clients of a Client JSON Protocol commonly need to figure out what

scripts/qapi/common.py

@@ -638,6 +638,27 @@ def add_name(name, info, meta, implicit=False):
     all_names[name] = meta
 
 
+def check_if(expr, info):
+
+    def check_if_str(ifcond, info):
+        if not isinstance(ifcond, str):
+            raise QAPISemError(
+                info, "'if' condition must be a string or a list of strings")
+        if ifcond == '':
+            raise QAPISemError(info, "'if' condition '' makes no sense")
+
+    ifcond = expr.get('if')
+    if ifcond is None:
+        return
+    if isinstance(ifcond, list):
+        if ifcond == []:
+            raise QAPISemError(info, "'if' condition [] is useless")
+        for elt in ifcond:
+            check_if_str(elt, info)
+    else:
+        check_if_str(ifcond, info)
+
+
 def check_type(info, source, value, allow_array=False,
                allow_dict=False, allow_optional=False,
                allow_metas=[]):
@@ -871,6 +892,8 @@ def check_keys(expr_elem, meta, required, optional=[]):
             raise QAPISemError(info,
                                "'%s' of %s '%s' should only use true value"
                                % (key, meta, name))
+        if key == 'if':
+            check_if(expr, info)
     for key in required:
         if key not in expr:
             raise QAPISemError(info, "Key '%s' is missing from %s '%s'"
@@ -899,28 +922,28 @@ def check_exprs(exprs):
 
         if 'enum' in expr:
             meta = 'enum'
-            check_keys(expr_elem, 'enum', ['data'], ['prefix'])
+            check_keys(expr_elem, 'enum', ['data'], ['if', 'prefix'])
             enum_types[expr[meta]] = expr
         elif 'union' in expr:
             meta = 'union'
             check_keys(expr_elem, 'union', ['data'],
-                       ['base', 'discriminator'])
+                       ['base', 'discriminator', 'if'])
             union_types[expr[meta]] = expr
         elif 'alternate' in expr:
             meta = 'alternate'
-            check_keys(expr_elem, 'alternate', ['data'])
+            check_keys(expr_elem, 'alternate', ['data'], ['if'])
         elif 'struct' in expr:
             meta = 'struct'
-            check_keys(expr_elem, 'struct', ['data'], ['base'])
+            check_keys(expr_elem, 'struct', ['data'], ['base', 'if'])
             struct_types[expr[meta]] = expr
         elif 'command' in expr:
             meta = 'command'
             check_keys(expr_elem, 'command', [],
                        ['data', 'returns', 'gen', 'success-response',
-                        'boxed', 'allow-oob', 'allow-preconfig'])
+                        'boxed', 'allow-oob', 'allow-preconfig', 'if'])
         elif 'event' in expr:
             meta = 'event'
-            check_keys(expr_elem, 'event', [], ['data', 'boxed'])
+            check_keys(expr_elem, 'event', [], ['data', 'boxed', 'if'])
         else:
             raise QAPISemError(expr_elem['info'],
                                "Expression is missing metatype")

tests/Makefile.include

@@ -442,6 +442,10 @@ qapi-schema += args-unknown.json
 qapi-schema += bad-base.json
 qapi-schema += bad-data.json
 qapi-schema += bad-ident.json
+qapi-schema += bad-if.json
+qapi-schema += bad-if-empty.json
+qapi-schema += bad-if-empty-list.json
+qapi-schema += bad-if-list.json
 qapi-schema += bad-type-bool.json
 qapi-schema += bad-type-dict.json
 qapi-schema += bad-type-int.json

tests/qapi-schema/bad-if-empty-list.err

@@ -0,0 +1 @@
+tests/qapi-schema/bad-if-empty-list.json:2: 'if' condition [] is useless

tests/qapi-schema/bad-if-empty-list.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/bad-if-empty-list.json

@@ -0,0 +1,3 @@
+# check empty 'if' list
+{ 'struct': 'TestIfStruct', 'data': { 'foo': 'int' },
+  'if': [] }

tests/qapi-schema/bad-if-empty.err

@@ -0,0 +1 @@
+tests/qapi-schema/bad-if-empty.json:2: 'if' condition '' makes no sense

tests/qapi-schema/bad-if-empty.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/bad-if-empty.json

@@ -0,0 +1,3 @@
+# check empty 'if'
+{ 'struct': 'TestIfStruct', 'data': { 'foo': 'int' },
+  'if': '' }

tests/qapi-schema/bad-if-list.err

@@ -0,0 +1 @@
+tests/qapi-schema/bad-if-list.json:2: 'if' condition '' makes no sense

tests/qapi-schema/bad-if-list.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/bad-if-list.json

@@ -0,0 +1,3 @@
+# check invalid 'if' content
+{ 'struct': 'TestIfStruct', 'data': { 'foo': 'int' },
+  'if': ['foo', ''] }

tests/qapi-schema/bad-if.err

@@ -0,0 +1 @@
+tests/qapi-schema/bad-if.json:2: 'if' condition must be a string or a list of strings

tests/qapi-schema/bad-if.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/bad-if.json

@@ -0,0 +1,3 @@
+# check invalid 'if' type
+{ 'struct': 'TestIfStruct', 'data': { 'foo': 'int' },
+  'if': { 'value': 'defined(TEST_IF_STRUCT)' } }

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

@@ -56,6 +56,9 @@
   'data': { 'string0': 'str',
             'dict1': 'UserDefTwoDict' } }
 
+{ 'struct': 'UserDefThree',
+  'data': { 'string0': 'str' } }
+
 # dummy struct to force generation of array types not otherwise mentioned
 { 'struct': 'ForceArrays',
   'data': { 'unused1':['UserDefOne'], 'unused2':['UserDefTwo'],
@@ -193,3 +196,26 @@
   'data': { 'a': ['__org.qemu_x-Enum'], 'b': ['__org.qemu_x-Struct'],
             'c': '__org.qemu_x-Union2', 'd': '__org.qemu_x-Alt' },
   'returns': '__org.qemu_x-Union1' }
+
+# test 'if' condition handling
+
+{ 'struct': 'TestIfStruct', 'data': { 'foo': 'int' },
+  'if': 'defined(TEST_IF_STRUCT)' }
+
+{ 'enum': 'TestIfEnum', 'data': [ 'foo', 'bar' ],
+  'if': 'defined(TEST_IF_ENUM)' }
+
+{ 'union': 'TestIfUnion', 'data': { 'foo': 'TestStruct' },
+  'if': 'defined(TEST_IF_UNION) && defined(TEST_IF_STRUCT)' }
+
+{ 'alternate': 'TestIfAlternate', 'data': { 'foo': 'int', 'bar': 'TestStruct' },
+  'if': 'defined(TEST_IF_ALT) && defined(TEST_IF_STRUCT)' }
+
+{ 'command': 'TestIfCmd', 'data': { 'foo': 'TestIfStruct' },
+  'returns': 'UserDefThree',
+  'if': ['defined(TEST_IF_CMD)', 'defined(TEST_IF_STRUCT)'] }
+
+{ 'command': 'TestCmdReturnDefThree', 'returns': 'UserDefThree' }
+
+{ 'event': 'TestIfEvent', 'data': { 'foo': 'TestIfStruct' },
+  'if': 'defined(TEST_IF_EVT) && defined(TEST_IF_STRUCT)' }