echo doesn't fail with no streams (#2555)

CHANGES.rst

@@ -30,6 +30,8 @@ Unreleased
     bytes with the replacement character (``�``). :issue:`2395`
 -   Remove unnecessary attempt to detect MSYS2 environment. :issue:`2355`
 -   Remove outdated and unnecessary detection of App Engine environment. :pr:`2554`
+-   ``echo()`` does not fail when no streams are attached, such as with ``pythonw`` on
+    Windows. :issue:`2415`
 
 
 Version 8.1.3

src/click/_compat.py

@@ -576,12 +576,17 @@ def isatty(stream: t.IO[t.Any]) -> bool:
 
 
 def _make_cached_stream_func(
-    src_func: t.Callable[[], t.TextIO], wrapper_func: t.Callable[[], t.TextIO]
-) -> t.Callable[[], t.TextIO]:
+    src_func: t.Callable[[], t.Optional[t.TextIO]],
+    wrapper_func: t.Callable[[], t.TextIO],
+) -> t.Callable[[], t.Optional[t.TextIO]]:
     cache: t.MutableMapping[t.TextIO, t.TextIO] = WeakKeyDictionary()
 
-    def func() -> t.TextIO:
+    def func() -> t.Optional[t.TextIO]:
         stream = src_func()
+
+        if stream is None:
+            return None
+
         try:
             rv = cache.get(stream)
         except Exception:

src/click/_termui_impl.py

@@ -10,6 +10,7 @@
 import time
 import typing as t
 from gettext import gettext as _
+from io import StringIO
 from types import TracebackType
 
 from ._compat import _default_text_stdout
@@ -61,8 +62,15 @@ def __init__(
         self.show_pos = show_pos
         self.item_show_func = item_show_func
         self.label: str = label or ""
+
         if file is None:
             file = _default_text_stdout()
+
+            # There are no standard streams attached to write to. For example,
+            # pythonw on Windows.
+            if file is None:
+                file = StringIO()
+
         self.file = file
         self.color = color
         self.update_min_steps = update_min_steps
@@ -352,6 +360,12 @@ def generator(self) -> t.Iterator[V]:
 def pager(generator: t.Iterable[str], color: t.Optional[bool] = None) -> None:
     """Decide what method to use for paging through text."""
     stdout = _default_text_stdout()
+
+    # There are no standard streams attached to write to. For example,
+    # pythonw on Windows.
+    if stdout is None:
+        stdout = StringIO()
+
     if not isatty(sys.stdin) or not isatty(stdout):
         return _nullpager(stdout, generator, color)
     pager_cmd = (os.environ.get("PAGER", None) or "").strip()

src/click/utils.py

@@ -267,6 +267,11 @@ def echo(
         else:
             file = _default_text_stdout()
 
+        # There are no standard streams attached to write to. For example,
+        # pythonw on Windows.
+        if file is None:
+            return
+
     # Convert non bytes/text into the native string type.
     if message is not None and not isinstance(message, (str, bytes, bytearray)):
         out: t.Optional[t.Union[str, bytes]] = str(message)

tests/test_utils.py

@@ -43,6 +43,15 @@ def test_echo_custom_file():
     assert f.getvalue() == "hello\n"
 
 
+def test_echo_no_streams(monkeypatch, runner):
+    """echo should not fail when stdout and stderr are None with pythonw on Windows."""
+    with runner.isolation():
+        sys.stdout = None
+        sys.stderr = None
+        click.echo("test")
+        click.echo("test", err=True)
+
+
 @pytest.mark.parametrize(
     ("styles", "ref"),
     [