Redirecting to a variable should be possible (#20381)

* add tests

* fix formatting issues

* Make redirection to variable an experimental feature.

Update test to check for experimental feature status.
Set-Variable will still have the -append parameter, but if used when the experimental feature is disabled, a parameter binding error will result.

* Check to be sure provider is not null.

* update to use different FullyQualifiedErrorId

* use Experimental attribute for append parameter rather than runtime check.

* Revert "update to use different FullyQualifiedErrorId"

This reverts commit 8b34af1ac19ecdb821b34534e446ab129830c92f.

* Update src/Microsoft.PowerShell.Commands.Utility/commands/utility/Var.cs

Co-authored-by: Ilya <darpa@yandex.ru>

* Move remediation steps into resource.

Update Set-Variable -Append to be correct when -name and -value are used.
Add tests for the new behavior in Set-Variable.

* Change expected error for contrained language mode and redirection.

* Update src/Microsoft.PowerShell.Commands.Utility/commands/utility/Var.cs

Co-authored-by: Ilya <darpa@yandex.ru>

* Support redirection of native app.

Add tests to validate.

* testexe needs proper case to run on linux.

* Address codefactor issues 01.

* Update src/System.Management.Automation/engine/runtime/Operations/MiscOps.cs

Co-authored-by: Steve Lee <slee@microsoft.com>

* Update src/Microsoft.PowerShell.Commands.Utility/commands/utility/Var.cs

Co-authored-by: Steve Lee <slee@microsoft.com>

* Update src/System.Management.Automation/engine/runtime/Operations/MiscOps.cs

Co-authored-by: Steve Lee <slee@microsoft.com>

---------

Co-authored-by: Ilya <darpa@yandex.ru>
Co-authored-by: Steve Lee <slee@microsoft.com>

test/powershell/Modules/Microsoft.PowerShell.Security/ConstrainedLanguageRestriction.Tests.ps1

@@ -460,7 +460,7 @@ try
             $rs.Open()
             $pl = $rs.CreatePipeline('"Hello" > c:\temp\foo.txt')
 
-            $e = { $pl.Invoke() } | Should -Throw -ErrorId "CmdletInvocationException"
+            $e = { $pl.Invoke() } | Should -Throw -ErrorId "DriveNotFoundException"
 
             $rs.Dispose()
         }

test/powershell/Modules/Microsoft.PowerShell.Utility/Set-Variable.Tests.ps1

@@ -241,4 +241,47 @@ Describe "Set-Variable" -Tags "CI" {
 	    { Set-Variable globalVar -Value 1 -Scope local -Force } | Should -Not -Throw
 	}
     }
+
+    Context "Set-Variable -Append tests" {
+        BeforeAll {
+            if (! (Get-ExperimentalFeature PSRedirectToVariable).Enabled) {
+				$skipTest = $true
+			}
+
+			$testCases = @{ value = 2; Count = 2 },
+				@{ value = @(2,3,4); Count = 2},
+				@{ value = "abc",(Get-Process -Id $PID) ; count = 2}
+        }
+
+		It "Can append values <value> to a variable" -testCases $testCases {
+			param ($value, $count)
+
+			if ($skipTest) {
+				Set-ItResult -skip -because "Experimental Feature PSRedirectToVariable not enabled"
+				return
+			}
+
+			$variableName = "testVar"
+			Set-Variable -Name $variableName -Value 1
+			Set-Variable -Name $variableName -Value $value -Append
+
+			$observedValues = Get-Variable $variableName -Value
+
+			$observedValues.Count | Should -Be $count
+			$observedValues[0] | Should -Be 1
+
+			$observedValues[1] | Should -Be $value
+		}
+
+		It "Can use set-variable via streaming and append values" {
+			if ($skipTest) {
+				Set-ItResult -skip -because "Experimental Feature PSRedirectToVariable not enabled"
+				return
+			}
+
+			$testVar = 1
+			4..6 | Set-Variable -Name testVar -Append
+			$testVar | Should -Be @(1,4,5,6)
+		}
+    }
 }