SC2154 fails to trigger when assigning function `local globalvar="$globalvar"` (SC2269 also not triggered)

#### For bugs with existing features - Rule Id (if any, e.g. SC1000): SC2154 - My shellcheck version (`shellcheck --version` or "online"): online - [x] The rule's wiki page does not already cover this (e.g. https://shellcheck.net/wiki/SC2086) - [x] 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: ```bash #!/bin/bash f(){ ## protect globalvar from mutation in f() local globalvar="$globalvar" echo "$globalvar" } echo "$globalvar" ``` #### Here's what shellcheck currently says: ``` $ shellcheck myscript No issues detected! $ ``` #### Here's what I wanted or expected to see: ``` $ shellcheck myscript [Line 4:] local globalvar="$globalvar" ^-- [SC2154](https://www.shellcheck.net/wiki/SC2154) (warning): globalvar is referenced but not assigned. $ ``` or at least something like: ``` $ shellcheck myscript [Line 4:] local globalvar="$globalvar" ^-- [SC2269](https://www.shellcheck.net/wiki/SC2269) (info): This variable is assigned to itself, so the assignment does nothing. $ ``` or another rule like ``` (warning): This variable is assigned to itself, so the assignment does nothing as there is no global variable assigned. ``` or ``` (warning): This variable is assigned to itself, so the assignment does nothing if there is no globally-available variable, check to ensure. ```