lint - S011 no longer warns against 0{{a}} (#5841)

lint - S011 no longer warns against 0{{a}}

changes.d/5841.fix.md

@@ -0,0 +1 @@
+Improve handling of S011 to not warn if the # is '#$' (e.g. shell base arithmetic)

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': {

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}