ASCII color chars leaking into xml report file when using verbose flag

Problem description

A bug was noticed when displaying failing tests on CI with the -vv flag: the ASCII color characters are being printed inside the detailed diff.

The displayed output comes directly from xml file (generated with the --junitxml flag), which in fact carries the undesired characters as shown in the minimal example below. This happens only when pygments is also installed, with both -v and -vv flags.

This undesired behavior was noticed in all 8.* versions but not in 7.4, so it probably was introduced in 8.0 together with the improved verbose diffs change (changelog).

Output of pip list

Package        Version
-------------- -------
exceptiongroup 1.2.1
iniconfig      2.0.0
packaging      24.0
pip            21.2.4
pluggy         1.5.0
Pygments       2.18.0
pytest         8.2.1
setuptools     58.1.0
tomli          2.0.1

pytest and operating system versions

• SO (uname -a): Linux FLDEVWSV032 6.5.0-35-generic #35~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Tue May 7 09:00:52 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
• Python: 3.10.2
• pytest: 8.0.0, 8.1.0, 8.2.1

Minimal example

test_foo.py:

def test_foo() -> None:
    assert [1,2,3] == [3,2,1]

Running it:

foo.xml:

<?xml version="1.0" encoding="utf-8"?>
<testsuites>
	<testsuite name="pytest" errors="0" failures="1" skipped="0" tests="1" time="0.082" timestamp="2024-05-24T14:19:42.491202" hostname="FLDEVWSV032">
		<testcase classname="test_foo" name="test_foo" time="0.055">
			<failure message="assert [1, 2, 3] == [3, 2, 1]&#10;  &#10;  At index 0 diff: #x1B[0m#x1B[94m1#x1B[39;49;00m#x1B[90m#x1B[39;49;00m != #x1B[0m#x1B[94m3#x1B[39;49;00m#x1B[90m#x1B[39;49;00m&#10;  &#10;  Full diff:&#10;  #x1B[0m#x1B[90m #x1B[39;49;00m [#x1B[90m#x1B[39;49;00m&#10;  #x1B[92m+     1,#x1B[39;49;00m#x1B[90m#x1B[39;49;00m&#10;  #x1B[92m+     2,#x1B[39;49;00m#x1B[90m#x1B[39;49;00m&#10;  #x1B[90m #x1B[39;49;00m     3,#x1B[90m#x1B[39;49;00m&#10;  #x1B[91m-     2,#x1B[39;49;00m#x1B[90m#x1B[39;49;00m&#10;  #x1B[91m-     1,#x1B[39;49;00m#x1B[90m#x1B[39;49;00m&#10;  #x1B[90m #x1B[39;49;00m ]#x1B[90m#x1B[39;49;00m">def test_foo() -&gt; None:
&gt;       assert [1,2,3] == [3,2,1]
E       assert [1, 2, 3] == [3, 2, 1]
E         
E         At index 0 diff: #x1B[0m#x1B[94m1#x1B[39;49;00m#x1B[90m#x1B[39;49;00m != #x1B[0m#x1B[94m3#x1B[39;49;00m#x1B[90m#x1B[39;49;00m
E         
E         Full diff:
E         #x1B[0m#x1B[90m #x1B[39;49;00m [#x1B[90m#x1B[39;49;00m
E         #x1B[92m+     1,#x1B[39;49;00m#x1B[90m#x1B[39;49;00m
E         #x1B[92m+     2,#x1B[39;49;00m#x1B[90m#x1B[39;49;00m
E         #x1B[90m #x1B[39;49;00m     3,#x1B[90m#x1B[39;49;00m
E         #x1B[91m-     2,#x1B[39;49;00m#x1B[90m#x1B[39;49;00m
E         #x1B[91m-     1,#x1B[39;49;00m#x1B[90m#x1B[39;49;00m
E         #x1B[90m #x1B[39;49;00m ]#x1B[90m#x1B[39;49;00m

test_foo.py:2: AssertionError</failure>
		</testcase>
	</testsuite>
</testsuites

For comparison, without having pygments installed the xml looks like this:

<?xml version="1.0" encoding="utf-8"?>
<testsuites>
	<testsuite name="pytest" errors="0" failures="1" skipped="0" tests="1" time="0.028" timestamp="2024-05-24T14:22:36.093080" hostname="FLDEVWSV032">
		<testcase classname="test_foo" name="test_foo" time="0.001">
			<failure message="assert [1, 2, 3] == [3, 2, 1]&#10;  &#10;  At index 0 diff: 1 != 3&#10;  &#10;  Full diff:&#10;    [&#10;  +     1,&#10;  +     2,&#10;        3,&#10;  -     2,&#10;  -     1,&#10;    ]">def test_foo() -&gt; None:
&gt;       assert [1,2,3] == [3,2,1]
E       assert [1, 2, 3] == [3, 2, 1]
E         
E         At index 0 diff: 1 != 3
E         
E         Full diff:
E           [
E         +     1,
E         +     2,
E               3,
E         -     2,
E         -     1,
E           ]

test_foo.py:2: AssertionError</failure>
		</testcase>
	</testsuite>
</testsuites>

If confirmed, I'd be happy to submit a PR fixing this.