Fix printing of emoji on Windows when stdout is redirected

This is most apparent when black is run via pre-commit which does
`subprocess.Popen(stdout=PIPE)`.

One option around this would be to instruct users to set `PYTHONUTF8=1`,
but that is not a very good approach, as basically everything supports
UTF-8 these days.

This fix was inspired by pycln and hadialqattan/pycln#54

CHANGES.md

@@ -42,6 +42,9 @@
 
 <!-- Changes to Black's terminal output and error messages -->
 
+- Force output messages to always be UTF-8 on Windows (so we can see the emoji), even if
+  terminal is redirected or captured (#3374)
+
 ### _Blackd_
 
 <!-- Changes to blackd -->

src/black/__init__.py

@@ -1393,6 +1393,16 @@ def patch_click() -> None:
 
 
 def patched_main() -> None:
+    #: Fixes errors with emoji in  Windows terminals when output is redirected
+    # (i.e. pre-commit): https://github.com/psf/black/issues/3156
+    if "pytest" not in sys.modules and sys.platform == "win32":
+        sys.stdout = io.TextIOWrapper(
+            sys.stdout.buffer, encoding="utf-8"
+        )  # pragma: nocover
+        sys.stderr = io.TextIOWrapper(
+            sys.stderr.buffer, encoding="utf-8"
+        )  # pragma: nocover
+
     # PyInstaller patches multiprocessing to need freeze_support() even in non-Windows
     # environments so just assume we always need to call it if frozen.
     if getattr(sys, "frozen", False):