[PULL,07/25] qapi/schema: declare type for QAPISchemaArrayType.element_type

Commit Message

Markus Armbruster April 24, 2024, 8:16 a.m. UTC

From: John Snow <[e-mail]>

A QAPISchemaArrayType's element type gets resolved only during .check().
We have QAPISchemaArrayType.__init__() initialize self.element_type =
None, and .check() assign the actual type.  Using .element_type before
.check() is wrong, and hopefully crashes due to the value being None.
Works.

However, it makes for awkward typing.  With .element_type:
Optional[QAPISchemaType], mypy is of course unable to see that it's None
before .check(), and a QAPISchemaType after.  To help it over the hump,
we'd have to assert self.element_type is not None before all the (valid)
uses.  The assertion catches invalid uses, but only at run time; mypy
can't flag them.

Instead, declare .element_type in .__init__() as QAPISchemaType
*without* initializing it.  Using .element_type before .check() now
certainly crashes, which is an improvement.  Mypy still can't flag
invalid uses, but that's okay.

Signed-off-by: John Snow <[e-mail]>
Reviewed-by: Markus Armbruster <[e-mail]>
Signed-off-by: Markus Armbruster <[e-mail]>
Message-ID: <[e-mail]>
---
 scripts/qapi/schema.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
index 307f8af01a..48f157fb91 100644
--- a/scripts/qapi/schema.py
+++ b/scripts/qapi/schema.py
@@ -381,7 +381,7 @@  def __init__(self, name, info, element_type):
         super().__init__(name, info, None)
         assert isinstance(element_type, str)
         self._element_type_name = element_type
-        self.element_type = None
+        self.element_type: QAPISchemaType
 
     def need_has_if_optional(self):
         # When FOO is an array, we still need has_FOO to distinguish