Remove flag completely

Author: cdce8p

CHANGELOG.md

@@ -11,10 +11,9 @@ Support for this will be dropped in the first half of 2026!
 
 Contributed by Marc Mueller (PR [20156](https://github.com/python/mypy/pull/20156)).
 
-### Deprecated Flag: `--force-union-syntax`
+### Removed Flag: `--force-union-syntax`
 
-Mypy only supports Python 3.10+. The `--force-union-syntax` flag is now
-deprecated, and a no-op. It will be removed in a future version.
+Mypy only supports Python 3.10+. Removed the `--force-union-syntax` flag as it's no longer necessary.
 
 Contributed by Marc Mueller (PR [20405](https://github.com/python/mypy/pull/20405))
 

mypy/main.py

@@ -820,11 +820,6 @@ def add_invertible_flag(
         "--force-uppercase-builtins", default=False, help=argparse.SUPPRESS, group=none_group
     )
 
-    # This flag is deprecated, Mypy only supports Python 3.10+
-    add_invertible_flag(
-        "--force-union-syntax", default=False, help=argparse.SUPPRESS, group=none_group
-    )
-
     lint_group = parser.add_argument_group(
         title="Configuring warnings",
         description="Detect code that is sound but redundant or problematic.",
@@ -1545,9 +1540,6 @@ def set_strict_flags() -> None:
     if options.force_uppercase_builtins:
         print("Warning: --force-uppercase-builtins is deprecated; mypy only supports Python 3.9+")
 
-    if options.force_union_syntax:
-        print("Warning: --force-union-syntax is deprecated; mypy only supports Python 3.10+")
-
     # Set target.
     if special_opts.modules + special_opts.packages:
         options.build_type = BuildType.MODULE

mypy/options.py

@@ -412,7 +412,6 @@ def __init__(self) -> None:
         self.disable_memoryview_promotion = False
         # Deprecated, Mypy only supports Python 3.9+
         self.force_uppercase_builtins = False
-        self.force_union_syntax = False
 
         # Sets custom output format
         self.output: str | None = None
@@ -431,14 +430,6 @@ def use_lowercase_names(self) -> bool:
         )
         return True
 
-    def use_or_syntax(self) -> bool:
-        warnings.warn(
-            "options.use_or_syntax() is deprecated and will be removed in a future version",
-            DeprecationWarning,
-            stacklevel=2,
-        )
-        return True
-
     def use_star_unpack(self) -> bool:
         return self.python_version >= (3, 11)