PSUseDeclaredVarsMoreThanAssignment in read(only) scope

[iRon7]

Steps to reproduce

I am not sure whether this is a duplicate of #636 and/or the implication is completely understood:

Function Get-A {$a}
Function Get-B {
	$a = 1
	Get-A
}
Get-B

Expected behavior

No reported issue

Actual behavior

RuleName                            Severity     ScriptName Line  Message
--------                            --------     ---------- ----  -------
PSUseDeclaredVarsMoreThanAssignment Warning      Analyzer.p 3     The variable 'a' is assigned but never used.
s                                                s1

If an unexpected error was thrown then please report the full error details using e.g. $error[0] | Select-Object *

Used case:
https://github.com/iRon7/ConvertTo-Expression/blob/master/ConvertTo-Expression.ps1

RuleName                            Severity     ScriptName Line  Message
--------                            --------     ---------- ----  -------
PSUseDeclaredVarsMoreThanAssignment Warning      ConvertTo- 208   The variable 'Space' is assigned but never used.
s                                                Expression
                                                 .ps1
PSUseDeclaredVarsMoreThanAssignment Warning      ConvertTo- 208   The variable 'LineUp' is assigned but never used.
s                                                Expression
                                                 .ps1

Environment data

> $PSVersionTable
Name                           Value
----                           -----
PSVersion                      5.1.17134.407
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.17134.407
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

> (Get-Module -ListAvailable PSScriptAnalyzer).Version | ForEach-Object { $_.ToString() }
1.17.1

[bergmeister]

@iRon7 The rule implementation is limited in its analysis to a scriptblock, which is a function here, therefore it cannot see the 'usage'. Because PowerShell propagates all variables to lower scopes (i.e. when you call a function), one technically does not need to pass variables explicitly but it is highly discouraged from a code readability/maintainability perspective. Therefore I strongly suggest to add a parameter to your Get-A function so that you can see the flow of dependencies/arguments and this will also 'fix' the PSScriptAnalyzer warning.

[iRon7]

Thank you for the answer,
I think that I have oversimplified my mvce.
In my case, the concerned Get-A function has already a lot of parameters and the concerned variable $a merely is a public setting/mode (which less meaning) for every (recursive) function called down the line.

Anyways, I basically agree with your statement, but question whether there are any justified exceptions to this rule.
I have been thinking about this for quite some time and I do not know the answer...