From b96a4d0143c3a569f0a22b219edb64be2cd90d1f Mon Sep 17 00:00:00 2001
From: ColemanTom <15375218+ColemanTom@users.noreply.github.com>
Date: Fri, 24 Nov 2023 03:23:18 +1100
Subject: [PATCH] lint - S011 no longer warns against 0{{a}} (#5841)

lint - S011 no longer warns against 0{{a}}
---
 changes.d/5841.fix.md           | 1 +
 cylc/flow/scripts/lint.py       | 2 +-
 tests/unit/scripts/test_lint.py | 6 ++++++
 3 files changed, 8 insertions(+), 1 deletion(-)
 create mode 100644 changes.d/5841.fix.md

diff --git a/changes.d/5841.fix.md b/changes.d/5841.fix.md
new file mode 100644
index 00000000000..9e11386b8d0
--- /dev/null
+++ b/changes.d/5841.fix.md
@@ -0,0 +1 @@
+Improve handling of S011 to not warn if the # is '#$' (e.g. shell base arithmetic)
\ No newline at end of file
diff --git a/cylc/flow/scripts/lint.py b/cylc/flow/scripts/lint.py
index e3a08493a57..1246cb08688 100755
--- a/cylc/flow/scripts/lint.py
+++ b/cylc/flow/scripts/lint.py
@@ -437,7 +437,7 @@ def check_indentation(line: str) -> bool:
         'evaluate commented lines': True,
         FUNCTION: functools.partial(
             check_if_jinja2,
-            function=re.compile(r'(?<!{)#.*?{[{%]').findall
+            function=re.compile(r'(?<!{)#[^$].*?{[{%]').findall
         )
     },
     'S012': {
diff --git a/tests/unit/scripts/test_lint.py b/tests/unit/scripts/test_lint.py
index 23fccf3ccb6..57f40469c4b 100644
--- a/tests/unit/scripts/test_lint.py
+++ b/tests/unit/scripts/test_lint.py
@@ -335,6 +335,12 @@ def test_check_cylc_file_jinja2_comments():
     assert not any('S011' in msg for msg in lint.messages)
 
 
+def test_check_cylc_file_jinja2_comments_shell_arithmetic_not_warned():
+    """Jinja2 after a $((10#$variable)) should not warn"""
+    lint = lint_text('#!jinja2\na = b$((10#$foo+5)) {{ BAR }}', ['style'])
+    assert not any('S011' in msg for msg in lint.messages)
+
+
 @pytest.mark.parametrize(
     # 11 won't be tested because there is no jinja2 shebang
     'number', set(range(1, len(MANUAL_DEPRECATIONS) + 1)) - {11}