qapi/types qapi/visit: Generate built-in stuff into separate files

Linking code from multiple separate QAPI schemata into the same
program is possible, but involves some weirdness around built-in
types:

* We generate code for built-in types into .c only with option
  --builtins.  The user is responsible for generating code for exactly
  one QAPI schema per program with --builtins.

* We generate code for built-in types into .h regardless of
  --builtins, but guarded by #ifndef QAPI_VISIT_BUILTIN.  Because all
  copies of this code are exactly the same, including any combination
  of these headers works.

Replace this contraption by something more conventional: generate code
for built-in types into their very own files: qapi-builtin-types.c,
qapi-builtin-visit.c, qapi-builtin-types.h, qapi-builtin-visit.h, but
only with --builtins.  Obey --output-dir, but ignore --prefix for
them.

Make qapi-types.h include qapi-builtin-types.h.  With multiple
schemata you now have multiple qapi-types.[ch], but only one
qapi-builtin-types.[ch].  Same for qapi-visit.[ch] and
qapi-builtin-visit.[ch].

Bonus: if all you need is built-in stuff, you can include a much
smaller header.  To be exploited shortly.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20180211093607.27351-21-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
[eblake: fix octal constant for python 3]
Signed-off-by: Eric Blake <eblake@redhat.com>

scripts/qapi/visit.py

@@ -263,13 +263,27 @@ out:
                  c_name=c_name(name))
 
 
-class QAPISchemaGenVisitVisitor(QAPISchemaMonolithicCVisitor):
+class QAPISchemaGenVisitVisitor(QAPISchemaModularCVisitor):
 
-    def __init__(self, prefix, opt_builtins):
-        QAPISchemaMonolithicCVisitor.__init__(
+    def __init__(self, prefix):
+        QAPISchemaModularCVisitor.__init__(
             self, prefix, 'qapi-visit', ' * Schema-defined QAPI visitors',
             __doc__)
-        self._opt_builtins = opt_builtins
+        self._add_module(None, ' * Built-in QAPI visitors')
+        self._genc.preamble_add(mcgen('''
+#include "qemu/osdep.h"
+#include "qemu-common.h"
+#include "qapi/error.h"
+#include "qapi-builtin-visit.h"
+'''))
+        self._genh.preamble_add(mcgen('''
+#include "qapi/visitor.h"
+#include "qapi-builtin-types.h"
+
+''',
+                                      prefix=prefix))
+
+    def _begin_module(self, name):
         self._genc.preamble_add(mcgen('''
 #include "qemu/osdep.h"
 #include "qemu-common.h"
@@ -277,45 +291,21 @@ class QAPISchemaGenVisitVisitor(QAPISchemaMonolithicCVisitor):
 #include "qapi/qmp/qerror.h"
 #include "%(prefix)sqapi-visit.h"
 ''',
-                                      prefix=prefix))
+                                      prefix=self._prefix))
         self._genh.preamble_add(mcgen('''
-#include "qapi/visitor.h"
+#include "qapi-builtin-visit.h"
 #include "%(prefix)sqapi-types.h"
 
 ''',
-                                      prefix=prefix))
-        self._btin = guardstart('QAPI_VISIT_BUILTIN')
-
-    def visit_end(self):
-        # To avoid header dependency hell, we always generate
-        # declarations for built-in types in our header files and
-        # simply guard them.  See also opt_builtins (command line
-        # option -b).
-        self._btin += guardend('QAPI_VISIT_BUILTIN')
-        self._genh.preamble_add(self._btin)
-        self._btin = None
+                                      prefix=self._prefix))
 
     def visit_enum_type(self, name, info, values, prefix):
-        # Special case for our lone builtin enum type
-        # TODO use something cleaner than existence of info
-        if not info:
-            self._btin += gen_visit_decl(name, scalar=True)
-            if self._opt_builtins:
-                self._genc.add(gen_visit_enum(name))
-        else:
-            self._genh.add(gen_visit_decl(name, scalar=True))
-            self._genc.add(gen_visit_enum(name))
+        self._genh.add(gen_visit_decl(name, scalar=True))
+        self._genc.add(gen_visit_enum(name))
 
     def visit_array_type(self, name, info, element_type):
-        decl = gen_visit_decl(name)
-        defn = gen_visit_list(name, element_type)
-        if isinstance(element_type, QAPISchemaBuiltinType):
-            self._btin += decl
-            if self._opt_builtins:
-                self._genc.add(defn)
-        else:
-            self._genh.add(decl)
-            self._genc.add(defn)
+        self._genh.add(gen_visit_decl(name))
+        self._genc.add(gen_visit_list(name, element_type))
 
     def visit_object_type(self, name, info, base, members, variants):
         # Nothing to do for the special empty builtin
@@ -336,6 +326,6 @@ class QAPISchemaGenVisitVisitor(QAPISchemaMonolithicCVisitor):
 
 
 def gen_visit(schema, output_dir, prefix, opt_builtins):
-    vis = QAPISchemaGenVisitVisitor(prefix, opt_builtins)
+    vis = QAPISchemaGenVisitVisitor(prefix)
     schema.visit(vis)
-    vis.write(output_dir)
+    vis.write(output_dir, opt_builtins)