PSUseOutputTypeCorrectly/[OutputType()] fires incorrectly, reporting that a fn should return string when the function actually return array of strings

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Steps to reproduce

function Split-KeyValuePairFormatter {
  [OutputType('System.String[]')]
  [CmdletBinding()]
  param (
    [Parameter(Mandatory = $true)]
    [string]
    $Format,

    [string]
    $KeyConstituent,

    [string]
    $ValueConstituent,

    [string]
    $KeyPlaceHolder = "<%KEY%>",

    [string]
    $ValuePlaceHolder = "<%VALUE%>"
  )
  [string[]]$constituents = @();

   # IMPLEMENTATION CODE OMITTED, but you can see that the return statement
   # just returns the array declared as string[]

   return $constituents;
}

Expected behavior

No warning expected

Actual behavior

Error:

RuleName                            Severity     ScriptName Line  Message
--------                            --------     ---------- ----  -------
PSUseOutputTypeCorrectly            Information  split-key- 152   The cmdlet 'Split-KeyValuePairFormatter' returns an  
                                                 value-pair       object of type 'System.String' but this type is not  
                                                 -formatter       declared in the OutputType attribute.
                                                 .ps1

If I change OutputType to: [OutputType('System.String')], which is clearly wrong as it doesn't reflect the behaviour of the actual code, then there is no error. This does not seem right. As a work around, I'm having to declare an incorrect return type, ie System.string in [OutputType()], and put in a comment to indicate as such. Luckily, there is no effect on the functinality, but I can't omit the OutputType without PSScriptAnalyzer reporting a warning.

Environment data

> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      7.0.0
PSEdition                      Core
GitCommitId                    7.0.0
OS                             Microsoft Windows 10.0.18362
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

> (Get-Module -ListAvailable PSScriptAnalyzer).Version | ForEach-Object { $_.ToString() }
1.19.0
1.18.3

首先，使用 Split-KeyValuePairFormatter 示例复现 PSUseOutputTypeCorrectly 警告，并检查该规则对 OutputType('System.String[]') 的处理方式。将其推断出的返回类型与声明的数组类型进行比较。当该规则接受字符串数组返回值，而不要求错误地声明为 System.String 时，即表示完成。