SC2198 false positive

[maxpagani]

For bugs

• Rule Id: SC2198
• My shellcheck version: 0.8.0
• The rule's wiki page does not already cover this (e.g. https://shellcheck.net/wiki/SC2086)
• I tried on https://www.shellcheck.net/ and verified that this is still a problem on the latest commit

Here's a snippet or screenshot that shows the problem:

#!/usr/bin/env bash
if [ "${@: -1}" == "foo" ]
then
  echo "last arg is 'foo'"
fi

Here's what shellcheck currently says:

Arrays don't work as operands in [ ]. Use a loop (or concatenate with * instead of @).

Here's what I wanted or expected to see:

No error. The expression in the test is not a concatenation, but the extraction of last parameter.