[mypyc] Don't crash on non-inlinable final local reads (#15719)

Fixes mypyc/mypyc#852.
Fixes mypyc/mypyc#990.

Author: ichard26

mypyc/irbuild/builder.py

@@ -60,7 +60,7 @@
     UnionType,
     get_proper_type,
 )
-from mypy.util import split_target
+from mypy.util import module_prefix, split_target
 from mypy.visitor import ExpressionVisitor, StatementVisitor
 from mypyc.common import BITMAP_BITS, SELF_NAME, TEMP_ATTR_NAME
 from mypyc.crash import catch_errors
@@ -1023,7 +1023,7 @@ def emit_load_final(
         """
         if final_var.final_value is not None:  # this is safe even for non-native names
             return self.load_literal_value(final_var.final_value)
-        elif native:
+        elif native and module_prefix(self.graph, fullname):
             return self.load_final_static(fullname, self.mapper.type_to_rtype(typ), line, name)
         else:
             return None

mypyc/test-data/irbuild-basic.test

@@ -3337,6 +3337,32 @@ def foo(z):
 L0:
     return 1
 
+[case testFinalLocals]
+from typing import Final
+
+def inlined() -> str:
+    # XXX: the final type must be declared explicitly for Var.final_value to be set.
+    const: Final[str] = "Oppenheimer"
+    return const
+
+def local() -> str:
+    const: Final[str] = inlined()
+    return const
+[out]
+def inlined():
+    r0, const, r1 :: str
+L0:
+    r0 = 'Oppenheimer'
+    const = r0
+    r1 = 'Oppenheimer'
+    return r1
+def local():
+    r0, const :: str
+L0:
+    r0 = inlined()
+    const = r0
+    return const
+
 [case testDirectlyCall__bool__]
 class A:
     def __bool__(self) -> bool: