[PATCH v3 12/17] qapi/gen: write _genc/_genh access shims

[John Snow <jsnow@redhat.com>]

Many places assume they can access these fields without checking them
first to ensure they are defined. Eliminating the _genc and _genh fields
and replacing them with functional properties that check for correct
state can ease the typing overhead by eliminating the Optional[T] return
type.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 scripts/qapi/gen.py | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/scripts/qapi/gen.py b/scripts/qapi/gen.py
index b5505685e6e..4b5d3ea3a5b 100644
--- a/scripts/qapi/gen.py
+++ b/scripts/qapi/gen.py
@@ -244,11 +244,20 @@ def __init__(self,
         self._user_blurb = user_blurb
         self._builtin_blurb = builtin_blurb
         self._pydoc = pydoc
-        self._genc: Optional[QAPIGenC] = None
-        self._genh: Optional[QAPIGenH] = None
+        self._current_module: Optional[str] = None
         self._module: Dict[str, Tuple[QAPIGenC, QAPIGenH]] = {}
         self._main_module: Optional[str] = None
 
+    @property
+    def _genc(self) -> QAPIGenC:
+        assert self._current_module is not None
+        return self._module[self._current_module][0]
+
+    @property
+    def _genh(self) -> QAPIGenH:
+        assert self._current_module is not None
+        return self._module[self._current_module][1]
+
     @staticmethod
     def _module_dirname(name: str) -> str:
         if QAPISchemaModule.is_user_module(name):
@@ -279,7 +288,7 @@ def _add_module(self, name: str, blurb: str) -> None:
         genc = QAPIGenC(basename + '.c', blurb, self._pydoc)
         genh = QAPIGenH(basename + '.h', blurb, self._pydoc)
         self._module[name] = (genc, genh)
-        self._genc, self._genh = self._module[name]
+        self._current_module = name
 
     def write(self, output_dir: str, opt_builtins: bool = False) -> None:
         for name in self._module:
@@ -303,8 +312,7 @@ def visit_module(self, module: QAPISchemaModule) -> None:
             else:
                 # The built-in module has not been created.  No code may
                 # be generated.
-                self._genc = None
-                self._genh = None
+                self._current_module = None
         else:
             assert module.user_module, "Unexpected system module"
             self._add_module(module.name, self._user_blurb)
-- 
2.26.2