With those settings, a "line that doesn't adhere to current tabs settings" is basically "a line with spaces as indentation".
You can highlight such lines by searching:
/\v^\t* +\t*[^\s]
Broken down:
\v
− "very magic" mode so we don't have to use too many \
later (see :help /\v
)
^
− anchor to the start of the line.
\t*
− match zero or more tab characters.
+
− match one or more space characters.
\t*
− match zero or more tab characters again.
[^\s]
− match anything except a space character.
Or if you want to highlight the entire line, add .*
to the end to also match the rest of the line:
/\v^\t* +\t*[^\s].*
If you don't want to clobber your search history with this, you can use :match
:
:match Error /\v^\t* +\t*[^\s].*/
See :help :match
.