SC2154 triggers only once, even among unrelated functions

[mpol]

For bugs

• Rule Id: SC2154
• My shellcheck version (shellcheck --version or 'online'): online
• [x] I tried on shellcheck.net and verified that this is still a problem on the latest commit
• [ ] It's not reproducible on shellcheck.net, but I think that's because it's an OS, configuration or encoding issue

For new checks and feature suggestions

• [x] shellcheck.net (i.e. the latest commit) currently gives no useful warnings about this
• [x] I searched through https://github.com/koalaman/shellcheck/issues and didn't find anything related

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

#!/bin/bash

function something {
        echo "${a?}"
}

function unrelated {
        echo "$a"
}

unrelated

Here's what shellcheck currently says:

Here's what I wanted or expected to see:

[Line 8:](javascript:setPosition(8, 15))
        echo "$a"
              ^-- [SC2154](https://www.shellcheck.net/wiki/SC2154) (warning): a is referenced but not assigned.

Using the ? expansion in one place means that the variable being used without assignment will not be caught in the other unrelated function.