Support creating PS class instance that is not bound to any runspace (#3871)

src/System.Management.Automation/engine/runtime/Operations/ClassOps.cs

@@ -70,12 +70,17 @@ namespace System.Management.Automation.Internal
         /// It's not intended to be a public API, but because we generate type in a different assembly it has to be public.
         /// Return type should be SessionStateInternal, but it violates accessibility consistency, so we use object.
         /// </summary>
+        /// <remarks>
+        /// By default, PowerShell class instantiation usually happens in the same Runspace where the class is defined. In
+        /// that case, the created instance will be bound to the session state used to define that class in the Runspace.
+        /// However, if the instantiation happens in a different Runspace where the class is not defined, then the created
+        /// instance won't be bound to any session state.
+        /// </remarks>
         /// <returns>SessionStateInternal</returns>
         public object GetSessionState()
         {
             SessionStateInternal ss = null;
-            bool found = _stateMap.TryGetValue(Runspace.DefaultRunspace, out ss);
-            Diagnostics.Assert(found, "We always should be able to find corresponding SessionState");
+            _stateMap.TryGetValue(Runspace.DefaultRunspace, out ss);
             return ss;
         }
     }

test/powershell/Language/Classes/Scripting.Classes.MiscOps.Tests.ps1

@@ -43,4 +43,75 @@ Describe 'Misc Test' -Tags "CI" {
                 [C1]::new().Bar() | should be "1;2;3;"
         }
     }
+
+    Context 'Class instantiation' {
+        Class C1 {
+            [string] Foo() {
+                return (Get-TestText)
+            }
+        }
+
+        BeforeAll {
+            $ExpectedTextFromBoundInstance   = "Class C1 was defined in this Runspace"
+            $ExpectedTextFromUnboundInstance = "New Runspace without class C1 defined"
+
+            ## Define 'Get-TestText' in the current Runspace
+            function Get-TestText { return $ExpectedTextFromBoundInstance }
+
+            $NewRunspaceFunctionDefinitions = @"
+    ## Define 'Get-TestText' in the new Runspace
+    function Get-TestText { return '$ExpectedTextFromUnboundInstance' }
+    
+    ## Define the function to create an instance of the given type using the default constructor
+    function New-UnboundInstance([Type]`$type) { `$type::new() }
+    
+    ## Define the function to call 'Foo()' on the given C1 instance, and return the result
+    function Run-Foo(`$C1Instance) { `$C1Instance.Foo() }
+"@
+            ## Create a new Runspace and define helper functions in it
+            $powershell = [powershell]::Create()
+            $powershell.AddScript($NewRunspaceFunctionDefinitions).Invoke() > $null
+            $powershell.Commands.Clear()
+
+            function InstantiateInNewRunspace([Type]$type) {
+                try {
+                    $result = $powershell.AddCommand("New-UnboundInstance").AddParameter("type", $type).Invoke()
+                    $result.Count | Should Be 1 > $null
+                    return $result[0]
+                } finally {
+                    $powershell.Commands.Clear()
+                }
+            }
+
+            function RunFooInNewRunspace($instance) {
+                try {
+                    $result = $powershell.AddCommand("Run-Foo").AddParameter("C1Instance", $instance).Invoke()
+                    $result.Count | Should Be 1 > $null
+                    return $result[0]
+                } finally {
+                    $powershell.Commands.Clear()
+                }
+            }
+        }
+
+        AfterAll {
+            $powershell.Dispose()
+        }
+
+        It "Create instance that is bound to a SessionState" {
+            $instance = [C1]::new()
+            ## For a bound class instance, the execution of an instance method is
+            ## done in the Runspace/SessionState the instance is bound to.
+            $instance.Foo() | Should Be $ExpectedTextFromBoundInstance
+            RunFooInNewRunspace $instance | Should Be $ExpectedTextFromBoundInstance
+        }
+
+        It "Create instance that is NOT bound to a SessionState" {
+            $instance = InstantiateInNewRunspace ([C1])
+            ## For an unbound class instance, the execution of an instance method is done in
+            ## the Runspace/SessionState where the call to the instance method is made.
+            $instance.Foo() | Should Be $ExpectedTextFromBoundInstance
+            RunFooInNewRunspace $instance | Should Be $ExpectedTextFromUnboundInstance
+        }
+    }
 }