Fix strict equality with enum type with custom __eq__ (python#14518)

Fixes regression introduced in python#14513.

mypy/checkexpr.py

@@ -2970,7 +2970,7 @@ def visit_comparison_expr(self, e: ComparisonExpr) -> Type:
                     not local_errors.has_new_errors()
                     and cont_type
                     and self.dangerous_comparison(
-                        left_type, cont_type, original_container=right_type
+                        left_type, cont_type, original_container=right_type, prefer_literal=False
                     )
                 ):
                     self.msg.dangerous_comparison(left_type, cont_type, "container", e)
@@ -2988,21 +2988,19 @@ def visit_comparison_expr(self, e: ComparisonExpr) -> Type:
                 # testCustomEqCheckStrictEquality for an example.
                 if not w.has_new_errors() and operator in ("==", "!="):
                     right_type = self.accept(right)
-                    # Also flag non-overlapping literals in situations like:
-                    #    x: Literal['a', 'b']
-                    #    if x == 'c':
-                    #        ...
-                    left_type = try_getting_literal(left_type)
-                    right_type = try_getting_literal(right_type)
                     if self.dangerous_comparison(left_type, right_type):
+                        # Show the most specific literal types possible
+                        left_type = try_getting_literal(left_type)
+                        right_type = try_getting_literal(right_type)
                         self.msg.dangerous_comparison(left_type, right_type, "equality", e)
 
             elif operator == "is" or operator == "is not":
                 right_type = self.accept(right)  # validate the right operand
                 sub_result = self.bool_type()
-                left_type = try_getting_literal(left_type)
-                right_type = try_getting_literal(right_type)
                 if self.dangerous_comparison(left_type, right_type):
+                    # Show the most specific literal types possible
+                    left_type = try_getting_literal(left_type)
+                    right_type = try_getting_literal(right_type)
                     self.msg.dangerous_comparison(left_type, right_type, "identity", e)
                 method_type = None
             else:
@@ -3036,7 +3034,12 @@ def find_partial_type_ref_fast_path(self, expr: Expression) -> Type | None:
         return None
 
     def dangerous_comparison(
-        self, left: Type, right: Type, original_container: Type | None = None
+        self,
+        left: Type,
+        right: Type,
+        original_container: Type | None = None,
+        *,
+        prefer_literal: bool = True,
     ) -> bool:
         """Check for dangerous non-overlapping comparisons like 42 == 'no'.
 
@@ -3064,6 +3067,14 @@ def dangerous_comparison(
         if custom_special_method(left, "__eq__") or custom_special_method(right, "__eq__"):
             return False
 
+        if prefer_literal:
+            # Also flag non-overlapping literals in situations like:
+            #    x: Literal['a', 'b']
+            #    if x == 'c':
+            #        ...
+            left = try_getting_literal(left)
+            right = try_getting_literal(right)
+
         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

test-data/unit/check-expressions.test

@@ -2221,6 +2221,32 @@ int == y
 y == int
 [builtins fixtures/bool.pyi]
 
+[case testStrictEqualityAndEnumWithCustomEq]
+# flags: --strict-equality
+from enum import Enum
+
+class E1(Enum):
+    X = 0
+    Y = 1
+
+class E2(Enum):
+    X = 0
+    Y = 1
+
+    def __eq__(self, other: object) -> bool:
+        return bool()
+
+E1.X == E1.Y  # E: Non-overlapping equality check (left operand type: "Literal[E1.X]", right operand type: "Literal[E1.Y]")
+E2.X == E2.Y
+[builtins fixtures/bool.pyi]
+
+[case testStrictEqualityWithBytesContains]
+# flags: --strict-equality
+data = b"xy"
+b"x" in data
+[builtins fixtures/primitives.pyi]
+[typing fixtures/typing-full.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")