specialize progressbar(length=...) as ProgressBar[int]

CHANGES.rst

@@ -31,6 +31,8 @@ Unreleased
 -   When generating a command's name from a decorated function's name, the
     suffixes ``_command``, ``_cmd``, ``_group``, and ``_grp`` are removed.
     :issue:`2322`
+-   Specialized typing of ``progressbar(length=...)`` as ``ProgressBar[int]``.
+    :pr:`2630`
 
 
 Version 8.1.7

src/click/termui.py

@@ -284,6 +284,46 @@ def echo_via_pager(
     return pager(itertools.chain(text_generator, "\n"), color)
 
 
+@t.overload
+def progressbar(
+    *,
+    length: int,
+    label: str | None = None,
+    show_eta: bool = True,
+    show_percent: bool | None = None,
+    show_pos: bool = False,
+    fill_char: str = "#",
+    empty_char: str = "-",
+    bar_template: str = "%(label)s  [%(bar)s]  %(info)s",
+    info_sep: str = "  ",
+    width: int = 36,
+    color: bool | None = None,
+    update_min_steps: int = 1,
+) -> ProgressBar[int]:
+    ...
+
+
+@t.overload
+def progressbar(
+    iterable: cabc.Iterable[V] | None = None,
+    length: int | None = None,
+    label: str | None = None,
+    show_eta: bool = True,
+    show_percent: bool | None = None,
+    show_pos: bool = False,
+    item_show_func: t.Callable[[V | None], str | None] | None = None,
+    fill_char: str = "#",
+    empty_char: str = "-",
+    bar_template: str = "%(label)s  [%(bar)s]  %(info)s",
+    info_sep: str = "  ",
+    width: int = 36,
+    file: t.TextIO | None = None,
+    color: bool | None = None,
+    update_min_steps: int = 1,
+) -> ProgressBar[V]:
+    ...
+
+
 def progressbar(
     iterable: cabc.Iterable[V] | None = None,
     length: int | None = None,

tests/typing/typing_progressbar.py

@@ -0,0 +1,18 @@
+from typing_extensions import assert_type
+
+from click import progressbar
+from click._termui_impl import ProgressBar
+
+
+def test_length_is_int() -> None:
+    with progressbar(length=5) as bar:
+        assert_type(bar, ProgressBar[int])
+        for i in bar:
+            assert_type(i, int)
+
+
+def test_generic_on_iterable() -> None:
+    with progressbar(("hello", "world")) as bar:
+        assert_type(bar, ProgressBar[str])
+        for s in bar:
+            assert_type(s, str)