From 236e301b8ad9b78ee880baf12e98a826113dc59b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Filipe=20La=C3=ADns?= <lains@riseup.net>
Date: Tue, 19 Oct 2021 19:42:13 +0100
Subject: [PATCH] bpo-42174: fallback to sane values if the columns or lines
 are 0 in get_terminal_size (GH-29046)
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I considered only falling back when both were 0, but that still seems
wrong, and the highly popular rich[1] library does it this way, so I
thought we should probably inherit that behavior.

[1] https://github.com/willmcgugan/rich

Signed-off-by: Filipe Laíns <lains@riseup.net>

Co-authored-by: Łukasz Langa <lukasz@langa.pl>
---
 Doc/library/shutil.rst                                        | 4 ++++
 Lib/shutil.py                                                 | 4 ++--
 .../next/Library/2021-10-19-01-30-57.bpo-42174.O2w9bi.rst     | 2 ++
 3 files changed, 8 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2021-10-19-01-30-57.bpo-42174.O2w9bi.rst

diff --git a/Doc/library/shutil.rst b/Doc/library/shutil.rst
index 11c67074921..22d6dba9e1a 100644
--- a/Doc/library/shutil.rst
+++ b/Doc/library/shutil.rst
@@ -804,6 +804,10 @@ Querying the size of the output terminal
 
    .. versionadded:: 3.3
 
+   .. versionchanged:: 3.11
+      The ``fallback`` values are also used if :func:`os.get_terminal_size`
+      returns zeroes.
+
 .. _`fcopyfile`:
    http://www.manpagez.com/man/3/copyfile/
 
diff --git a/Lib/shutil.py b/Lib/shutil.py
index e544498fca7..949e024853c 100644
--- a/Lib/shutil.py
+++ b/Lib/shutil.py
@@ -1372,9 +1372,9 @@ def get_terminal_size(fallback=(80, 24)):
             # os.get_terminal_size() is unsupported
             size = os.terminal_size(fallback)
         if columns <= 0:
-            columns = size.columns
+            columns = size.columns or fallback[0]
         if lines <= 0:
-            lines = size.lines
+            lines = size.lines or fallback[1]
 
     return os.terminal_size((columns, lines))
 
diff --git a/Misc/NEWS.d/next/Library/2021-10-19-01-30-57.bpo-42174.O2w9bi.rst b/Misc/NEWS.d/next/Library/2021-10-19-01-30-57.bpo-42174.O2w9bi.rst
new file mode 100644
index 00000000000..412582ded3e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-10-19-01-30-57.bpo-42174.O2w9bi.rst
@@ -0,0 +1,2 @@
+:meth:`shutil.get_terminal_size` now falls back to sane values if the column
+or line count are 0.