False Positive AssignmentNotUsed inspection

[daFreeMan]

Rubberduck version information

Version 2.5.0.5410
OS: Microsoft Windows NT 10.0.17134.0, x64
Host Product: Microsoft Office 2016 x64
Host Version: 16.0.4966.1000
Host Executable: EXCEL.EXE

Description
A variable assignment in an error handler is flagged as Not Used, even though that's the Function's "return" variable and it is used in cleaning up the return.

To Reproduce

Public Function Foo() as Long
  Dim Sum as Long
  On Error Goto ErrorHandler
  Sum = 1/0
CleanExit:
  Foo = Sum
  Exit Function
ErrorHandler:
  Sum = -1 
  Resume CleanExit
End Function

Expected behavior
The Sum = -1 assignment in the ErrorHandler should not be flagged as unused.

Screenshots
N/A

Logfile
RubberduckLog.txt

Additional context
This will probably require full CPA to fix.

[MDoerner]

The problem here seems to be that the code path analysis does not account for jump statements like GoTo and Resume.

[BZngr]

There can be a reduction in false positives due to jump statements by evaluating the referenced 'jump-to' labels. If there is a potential of usage in the code below the jump-to label, the unused-assignment-candidate can be removed from the inspection results.

In the same way that ProcedureNotUsedInspection filters all Public Standard Module procedures from inspection results to avoid false positives - the above approach may avoid some false positives at the potential cost of missing some actual unused assignments. (Granted: the filter applied to ProcedureNotUsedInspection is a more significant 'win')

I have a local branch that accomplishes this. It evaluates Resume and GoTo statements that reference labels or linenumbers. Not included in the evaluation are On...GoTo statements.

I'm commenting here to get some feedback as to whether there is interest in reducing the false positives using this approach before creating a PR.

[daFreeMan]

(Just noticed your comment.)

I'm all for it.