Add missing container-parameters to Data

src/Pester.Runtime.ps1

@@ -2398,6 +2398,8 @@ function New-BlockContainerObject {
         $Data
     )
 
+    if ($null -eq $Data) { $Data = @{} }
+
     $type, $item = switch ($PSCmdlet.ParameterSetName) {
         "ScriptBlock" { "ScriptBlock", $ScriptBlock }
         "Path" { "File", (& $SafeCommands['Get-Item'] $Path) }
@@ -2624,3 +2626,34 @@ function Invoke-InNewScriptScope ([ScriptBlock] $ScriptBlock, $SessionState) {
 
     . $wrapper $Path $Data
 }
+
+function Add-MissingContainerParameters ($RootBlock, $Container, $CallingFunction) {
+    # Adds default values for container parameters not provided by the user.
+    # Also adds real parameter name as variable in Run-phase when alias was used, just like normal PowerShell will.
+
+    # Using AST to get parameter-names as $PSCmdLet.MyInvocation.MyCommand only works for advanced functions/scripts/cmdlets.
+    # No need to filter on parameter sets OR whether default values are set because Powershell adds all parameters (not aliases) as variables
+    # with default value or $null if not specified (probably to avoid error caused by inheritance).
+    $Ast = switch ($Container.Type) {
+        "ScriptBlock" { $container.Item.Ast }
+        "File" {
+            $externalScriptInfo = $CallingFunction.SessionState.InvokeCommand.GetCommand($Container.Item.PSPath, [System.Management.Automation.CommandTypes]::ExternalScript)
+            $externalScriptInfo.ScriptBlock.Ast
+        }
+        default { throw [System.ArgumentOutOfRangeException]"" }
+    }
+
+    if ($null -ne $Ast -and $null -ne $Ast.ParamBlock -and $Ast.ParamBlock.Parameters.Count -gt 0) {
+        $parametersToCheck = foreach ($param in $Ast.ParamBlock.Parameters) { $param.Name.VariablePath.UserPath }
+
+        foreach ($param in $parametersToCheck) {
+            $v = $CallingFunction.SessionState.PSVariable.Get($param)
+            if ((-not $RootBlock.Data.ContainsKey($param)) -and $v) {
+                if ($PesterPreference.Debug.WriteDebugMessages.Value) {
+                    Write-PesterDebugMessage -Scope Discovery "Container parameter '$param' is undefined, adding to container Data with default value $(Format-Nicely $v.Value)."
+                }
+                $RootBlock.Data.Add($param, $v.Value)
+            }
+        }
+    }
+}

src/functions/Context.ps1

@@ -93,6 +93,11 @@ https://pester.dev/docs/usage/testdrive
     }
 
     if ($ExecutionContext.SessionState.PSVariable.Get('invokedViaInvokePester')) {
+        if ($state.CurrentBlock.IsRoot -and $state.CurrentBlock.Blocks.Count -eq 0) {
+            # For undefined parameters in container, add parameter's default value to Data
+            Add-MissingContainerParameters -RootBlock $state.CurrentBlock -Container $container -CallingFunction $PSCmdlet
+        }
+
         if ($PSBoundParameters.ContainsKey('ForEach')) {
             if ($null -ne $ForEach -and 0 -lt @($ForEach).Count) {
                 New-ParametrizedBlock -Name $Name -ScriptBlock $Fixture -StartLine $MyInvocation.ScriptLineNumber -Tag $Tag -FrameworkData @{ CommandUsed = 'Context'; WrittenToScreen = $false } -Focus:$Focus -Skip:$Skip -Data $ForEach

src/functions/Describe.ps1

@@ -99,8 +99,12 @@ https://pester.dev/docs/usage/testdrive
         }
     }
 
-
     if ($ExecutionContext.SessionState.PSVariable.Get('invokedViaInvokePester')) {
+        if ($state.CurrentBlock.IsRoot -and $state.CurrentBlock.Blocks.Count -eq 0) {
+            # For undefined parameters in container, add parameter's default value to Data
+            Add-MissingContainerParameters -RootBlock $state.CurrentBlock -Container $container -CallingFunction $PSCmdlet
+        }
+
         if ($PSBoundParameters.ContainsKey('ForEach')) {
             if ($null -ne $ForEach -and 0 -lt @($ForEach).Count) {
                 New-ParametrizedBlock -Name $Name -ScriptBlock $Fixture -StartLine $MyInvocation.ScriptLineNumber -Tag $Tag -FrameworkData @{ CommandUsed = 'Describe'; WrittenToScreen = $false } -Focus:$Focus -Skip:$Skip -Data $ForEach

tst/Pester.RSpec.InNewProcess.ts.ps1

@@ -88,7 +88,7 @@ i -PassThru:$PassThru {
             $testpath = Join-Path $temp "$([Guid]::NewGuid().Guid).tests.ps1"
 
             try {
-                $c = 'param([Parameter(Mandatory)]$File) Describe "d - <File>" { It "i" { 1 | Should -Be 1 } }'
+                $c = 'param([Parameter(Mandatory)]$File, $MyValue = 1) Describe "d - <File>" { It "i" { $MyValue | Should -Be 1 } }'
                 Set-Content -Path $testpath -Value $c
 
                 $sb = [scriptblock]::Create("`$global:PesterPreference = [PesterConfiguration]@{Output=@{Verbosity='Detailed'}}; & $testpath -File 'demo.ps1'")
@@ -110,7 +110,7 @@ i -PassThru:$PassThru {
             $testpath = Join-Path $temp "$([Guid]::NewGuid().Guid).tests.ps1"
 
             try {
-                $c = 'param([Parameter(Mandatory)]$File) Context "c - <File>" { It "i" { 1 | Should -Be 1 } }'
+                $c = 'param([Parameter(Mandatory)]$File, $MyValue = 1) Context "c - <File>" { It "i" { $MyValue | Should -Be 1 } }'
                 Set-Content -Path $testpath -Value $c
 
                 $sb = [scriptblock]::Create("`$global:PesterPreference = [PesterConfiguration]@{Output=@{Verbosity='Detailed'}}; & $testpath -File 'demo.ps1'")