From 301072dd35ea54145b25ba0c99c79af04df087bc Mon Sep 17 00:00:00 2001
From: Marc Mueller <30130371+cdce8p@users.noreply.github.com>
Date: Fri, 25 Jun 2021 23:52:17 +0200
Subject: [PATCH] Bugfix

---
 mypy/fastparse.py                     |  7 ++++--
 test-data/unit/check-overloading.test | 31 +++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/mypy/fastparse.py b/mypy/fastparse.py
index 56723ee295f04..efdbb29cd787c 100644
--- a/mypy/fastparse.py
+++ b/mypy/fastparse.py
@@ -509,11 +509,12 @@ def fix_function_overloads(self, stmts: List[Statement]) -> List[Statement]:
                     and len(stmt.body[0].body) == 1
                     and isinstance(
                         stmt.body[0].body[0], (Decorator, OverloadedFuncDef))
-                    and infer_reachability_of_if_statement(
+                    and infer_reachability_of_if_statement(  # type: ignore[func-returns-value]
                         stmt, self.options
-                    ) is None  # type: ignore[func-returns-value]
+                    ) is None
                     and stmt.body[0].is_unreachable is False
                 ):
+                    current_overload = []
                     current_overload_name = stmt.body[0].body[0].name
                     last_if_stmt = stmt
                     last_if_overload = stmt.body[0].body[0]
@@ -526,6 +527,8 @@ def fix_function_overloads(self, stmts: List[Statement]) -> List[Statement]:
             ret.append(current_overload[0])
         elif len(current_overload) > 1:
             ret.append(OverloadedFuncDef(current_overload))
+        elif last_if_stmt is not None:
+            ret.append(last_if_stmt)
         return ret
 
     def in_method_scope(self) -> bool:
diff --git a/test-data/unit/check-overloading.test b/test-data/unit/check-overloading.test
index d6831c03a69a0..8cf7833056ced 100644
--- a/test-data/unit/check-overloading.test
+++ b/test-data/unit/check-overloading.test
@@ -5496,3 +5496,34 @@ def f2(g: Any) -> Any: ...
 reveal_type(f2(42))  # N: Revealed type is "__main__.A"
 reveal_type(f2("Hello"))  # N: Revealed type is "__main__.A" \
                           # E: Argument 1 to "f2" has incompatible type "str"; expected "int"
+
+[case testOverloadIfOldStyle]
+# flags: --always-false var_false --always-true var_true
+from typing import overload, Any
+
+class A: ...
+class B: ...
+
+var_true = True
+var_false = False
+
+if var_false:
+    @overload
+    def f1(g: int) -> A: ...
+    @overload
+    def f1(g: str) -> B: ...
+    def f1(g: Any) -> Any: ...
+elif var_true:
+    @overload
+    def f1(g: int) -> A: ...
+    @overload
+    def f1(g: str) -> B: ...
+    def f1(g: Any) -> Any: ...
+else:
+    @overload
+    def f1(g: int) -> A: ...
+    @overload
+    def f1(g: str) -> B: ...
+    def f1(g: Any) -> Any: ...
+reveal_type(f1(42))  # N: Revealed type is "__main__.A"
+reveal_type(f1("Hello"))  # N: Revealed type is "__main__.B"