Disable --strict-equality inside functions that have type variables with value restrictions

mypy/checkexpr.py

@@ -2028,6 +2028,19 @@ def dangerous_comparison(self, left: Type, right: Type,
         """
         if not self.chk.options.strict_equality:
             return False
+        if self.chk.binder.is_unreachable_warning_suppressed():
+            # We are inside a function that contains type variables with value restrictions in
+            # its signature. In this case we just suppress all strict-equality checks to avoid
+            # false positives for code like:
+            #
+            #     T = TypeVar('T', str, int)
+            #     def f(x: T) -> T:
+            #         if x == 0:
+            #             ...
+            #         return x
+            #
+            # TODO: find a way of disabling the check only for types resulted from the expansion.
+            return False
         if isinstance(left, NoneType) or isinstance(right, NoneType):
             return False
         if isinstance(left, UnionType) and isinstance(right, UnionType):

test-data/unit/check-expressions.test

@@ -2259,6 +2259,18 @@ class Custom:
 Custom() == int()
 [builtins fixtures/bool.pyi]
 
+[case testStrictEqualityDisabledWithTypeVarRestrictions]
+# flags: --strict-equality
+from typing import TypeVar
+
+T = TypeVar('T', str, int)
+
+def f(x: T) -> T:
+    if x == int():  # OK
+        ...
+    return x
+[builtins fixtures/bool.pyi]
+
 [case testUnimportedHintAny]
 def f(x: Any) -> None:  # E: Name 'Any' is not defined \
                         # N: Did you forget to import it from "typing"? (Suggestion: "from typing import Any")