Only do the lightweight type inferencing thing outside functions. Roll back changes to check-typevar-values.test.

Author: Guido van Rossum

mypy/semanal.py

@@ -1083,10 +1083,14 @@ def visit_assignment_stmt(self, s: AssignmentStmt) -> None:
 
     def analyze_simple_literal_type(self, rvalue: Node) -> Optional[Type]:
         """Return builtins.int if rvalue is an int literal, etc."""
-        if self.weak_opts or not self.lightweight_type_check:
+        if self.weak_opts or not self.lightweight_type_check or self.function_stack:
             # Skip this if any weak options are set.
             # Also skip if lightweight type check not requested.
             # This is mostly to avoid breaking unit tests.
+            # Also skip inside a function; this is to avoid confusing
+            # the code that handles dead code due to isinstance()
+            # inside type variables with value restrictions (like
+            # AnyStr).
             return None
         if isinstance(rvalue, IntExpr):
             return self.named_type_or_none('builtins.int')

test-data/unit/check-typevar-values.test

@@ -145,9 +145,9 @@ from typing import TypeVar
 T = TypeVar('T', int, str)
 def f(x: T) -> T:
     if isinstance(x, int):
-        y = 1+0
+        y = 1
     else:
-        y = ''+''
+        y = ''
     return y
 [builtins fixtures/isinstance.py]
 
@@ -156,7 +156,7 @@ from typing import TypeVar
 T = TypeVar('T', int, str)
 def f(x: T) -> T:
     if isinstance(x, int):
-        y = 1+0
+        y = 1
     else:
         y = object()
     return y # E: Incompatible return value type (got "object", expected "str")