From 4a18fc3757efa666f9769e7521524bc57cbb2e7f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C5=82=20G=C3=B3rny?= <mgorny@gentoo.org>
Date: Sat, 16 Dec 2023 19:15:22 +0100
Subject: [PATCH] Fix handling empty values of NO_COLOR and FORCE_COLOR

Fix handling NO_COLOR and FORCE_COLOR environment variables to correctly
be ignored when they are set to an empty value, as defined
in the specification:

> Command-line software which adds ANSI color to its output by default
> should check for a NO_COLOR environment variable that, when present
> *and not an empty string* (regardless of its value), prevents
> the addition of ANSI color.

(emphasis mine, https://no-color.org/)

The same is true of FORCE_COLOR, https://force-color.org/.
---
 AUTHORS                           | 1 +
 changelog/11712.bugfix.rst        | 1 +
 doc/en/reference/reference.rst    | 4 ++--
 src/_pytest/_io/terminalwriter.py | 4 ++--
 testing/io/test_terminalwriter.py | 6 ++++++
 5 files changed, 12 insertions(+), 4 deletions(-)
 create mode 100644 changelog/11712.bugfix.rst

diff --git a/AUTHORS b/AUTHORS
index bb273edcc..42cfd0be2 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -266,6 +266,7 @@ Michael Goerz
 Michael Krebs
 Michael Seifert
 Michal Wajszczuk
+Michał Górny
 Michał Zięba
 Mickey Pashov
 Mihai Capotă
diff --git a/changelog/11712.bugfix.rst b/changelog/11712.bugfix.rst
new file mode 100644
index 000000000..416d76149
--- /dev/null
+++ b/changelog/11712.bugfix.rst
@@ -0,0 +1 @@
+Fixed handling ``NO_COLOR`` and ``FORCE_COLOR`` to ignore an empty value.
diff --git a/doc/en/reference/reference.rst b/doc/en/reference/reference.rst
index 3054109ba..b2b63a89e 100644
--- a/doc/en/reference/reference.rst
+++ b/doc/en/reference/reference.rst
@@ -1146,13 +1146,13 @@ When set to ``0``, pytest will not use color.
 
 .. envvar:: NO_COLOR
 
-When set (regardless of value), pytest will not use color in terminal output.
+When set to a non-empty string (regardless of value), pytest will not use color in terminal output.
 ``PY_COLORS`` takes precedence over ``NO_COLOR``, which takes precedence over ``FORCE_COLOR``.
 See `no-color.org <https://no-color.org/>`__ for other libraries supporting this community standard.
 
 .. envvar:: FORCE_COLOR
 
-When set (regardless of value), pytest will use color in terminal output.
+When set to a non-empty string (regardless of value), pytest will use color in terminal output.
 ``PY_COLORS`` and ``NO_COLOR`` take precedence over ``FORCE_COLOR``.
 
 Exceptions
diff --git a/src/_pytest/_io/terminalwriter.py b/src/_pytest/_io/terminalwriter.py
index 934278b93..b6eceb75a 100644
--- a/src/_pytest/_io/terminalwriter.py
+++ b/src/_pytest/_io/terminalwriter.py
@@ -29,9 +29,9 @@ def should_do_markup(file: TextIO) -> bool:
         return True
     if os.environ.get("PY_COLORS") == "0":
         return False
-    if "NO_COLOR" in os.environ:
+    if os.environ.get("NO_COLOR"):
         return False
-    if "FORCE_COLOR" in os.environ:
+    if os.environ.get("FORCE_COLOR"):
         return True
     return (
         hasattr(file, "isatty") and file.isatty() and os.environ.get("TERM") != "dumb"
diff --git a/testing/io/test_terminalwriter.py b/testing/io/test_terminalwriter.py
index b5a04a99f..cf1c7fa90 100644
--- a/testing/io/test_terminalwriter.py
+++ b/testing/io/test_terminalwriter.py
@@ -213,6 +213,12 @@ def test_should_not_do_markup_NO_COLOR_and_FORCE_COLOR(
     assert_color_not_set()
 
 
+def test_empty_NO_COLOR_ignored(monkeypatch: MonkeyPatch) -> None:
+    monkeypatch.setitem(os.environ, "NO_COLOR", "")
+    monkeypatch.setitem(os.environ, "FORCE_COLOR", "1")
+    assert_color_set()
+
+
 class TestTerminalWriterLineWidth:
     def test_init(self) -> None:
         tw = terminalwriter.TerminalWriter()