[PATCH 07/16] qapi/expr.py: Add casts in a few select cases

[John Snow]

Casts are instructions to the type checker only, they aren't "safe" and
should probably be avoided in general. In this case, when we perform
type checking on a nested structure, the type of each field does not
"stick".

We don't need to assert that something is a str if we've already checked
that it is -- use a cast instead for these cases.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 scripts/qapi/expr.py | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/scripts/qapi/expr.py b/scripts/qapi/expr.py
index 633f9b9172..4a3352a2bd 100644
--- a/scripts/qapi/expr.py
+++ b/scripts/qapi/expr.py
@@ -15,7 +15,11 @@
 # See the COPYING file in the top-level directory.
 
 import re
-from typing import MutableMapping, Optional
+from typing import (
+    MutableMapping,
+    Optional,
+    cast,
+)
 
 from .common import c_name
 from .error import QAPISemError
@@ -225,7 +229,7 @@ def check_enum(expr, info):
 
 
 def check_struct(expr, info):
-    name = expr['struct']
+    name = cast(str, expr['struct'])  # Asserted in check_exprs
     members = expr['data']
 
     check_type(members, info, "'data'", allow_dict=name)
@@ -233,7 +237,7 @@ def check_struct(expr, info):
 
 
 def check_union(expr, info):
-    name = expr['union']
+    name = cast(str, expr['union'])  # Asserted in check_exprs
     base = expr.get('base')
     discriminator = expr.get('discriminator')
     members = expr['data']
@@ -330,7 +334,7 @@ def check_exprs(exprs):
         else:
             raise QAPISemError(info, "expression is missing metatype")
 
-        name = expr[meta]
+        name = cast(str, expr[meta])  # asserted right below:
         check_name_is_str(name, info, "'%s'" % meta)
         info.set_defn(meta, name)
         check_defn_name_str(name, info, meta)
-- 
2.26.2