Private/Get-ConfigurationDataDictionaryValue.ps1

@@ -0,0 +1,22 @@
+function Get-ConfigurationDataDictionaryValue {
+    [CmdletBinding()]
+    Param(
+        [Parameter(Mandatory=$true)]
+        [System.Collections.IDictionary]
+        $Dictionary,
+
+        [Parameter(Mandatory=$true)]
+        [string]
+        $Key,
+
+        [Parameter(Mandatory=$false)]
+        [AllowNull()]
+        $DefaultValue = $null
+    )
+
+    if(Test-ConfigurationDataDictionaryKey -Dictionary $Dictionary -Key $Key){
+        return $Dictionary[$Key]
+    }
+
+    return $DefaultValue
+}

Private/Get-ConfigurationDataTemplateExtends.ps1

@@ -0,0 +1,31 @@
+function Get-ConfigurationDataTemplateExtends {
+    [CmdletBinding()]
+    Param(
+        [Parameter(Mandatory=$true)]
+        [System.Collections.IDictionary]
+        $ConfigurationData
+    )
+
+    $Extends = $null
+
+    if(Test-ConfigurationDataDictionaryKey -Dictionary $ConfigurationData -Key "Metadata"){
+        $Metadata = Get-ConfigurationDataDictionaryValue -Dictionary $ConfigurationData -Key "Metadata"
+        if($Metadata -is [System.Collections.IDictionary] -and (Test-ConfigurationDataDictionaryKey -Dictionary $Metadata -Key "Extends")){
+            $Extends = Get-ConfigurationDataDictionaryValue -Dictionary $Metadata -Key "Extends"
+        }
+    }
+
+    if($null -eq $Extends -and (Test-ConfigurationDataDictionaryKey -Dictionary $ConfigurationData -Key "Extends")){
+        $Extends = Get-ConfigurationDataDictionaryValue -Dictionary $ConfigurationData -Key "Extends"
+    }
+
+    if($null -eq $Extends){
+        return @()
+    }
+
+    if($Extends -is [System.Array] -and $Extends -isnot [string]){
+        return @($Extends)
+    }
+
+    return @($Extends)
+}

Private/Get-ConfigurationDataTemplateMergeFile.ps1

@@ -0,0 +1,42 @@
+function Get-ConfigurationDataTemplateMergeFile {
+    [CmdletBinding()]
+    Param(
+        [Parameter(Mandatory=$true)]
+        [string]
+        $Path,
+
+        [Parameter(Mandatory=$false)]
+        [hashtable]
+        $Visited = @{}
+    )
+
+    $ResolvedPath = Resolve-ConfigurationDataTemplatePath -Path $Path
+
+    if($Visited.ContainsKey($ResolvedPath)){
+        $Chain = @($Visited.Keys + $ResolvedPath) -join " -> "
+        throw "Circular configuration data template inheritance detected: $Chain"
+    }
+
+    $Visited[$ResolvedPath] = $true
+
+    $ConfigurationData = Import-PowerShellDataFile -Path $ResolvedPath
+    if($ConfigurationData -isnot [System.Collections.IDictionary]){
+        throw "Configuration data template [$ResolvedPath] must contain a hashtable."
+    }
+
+    $Files = @()
+    $BasePath = Split-Path -Path $ResolvedPath -Parent
+    foreach($ParentPath in @(Get-ConfigurationDataTemplateExtends -ConfigurationData $ConfigurationData)){
+        if([string]::IsNullOrWhiteSpace([string]$ParentPath)){
+            continue
+        }
+
+        $ResolvedParentPath = Resolve-ConfigurationDataTemplatePath -Path ([string]$ParentPath) -BasePath $BasePath
+        $Files += @(Get-ConfigurationDataTemplateMergeFile -Path $ResolvedParentPath -Visited $Visited)
+    }
+
+    $Files += $ResolvedPath
+    $Visited.Remove($ResolvedPath)
+
+    return @($Files)
+}

Private/Merge-ConfigurationDataTemplateFile.ps1

@@ -0,0 +1,49 @@
+function Merge-ConfigurationDataTemplateFile {
+    [CmdletBinding()]
+    Param(
+        [Parameter(Mandatory=$true)]
+        [string[]]
+        $Path,
+
+        [Parameter(Mandatory=$false)]
+        [switch]
+        $PassThru
+    )
+
+    $MergeFiles = @()
+    $AddedFiles = @{}
+
+    foreach($Item in $Path){
+        foreach($File in @(Get-ConfigurationDataTemplateMergeFile -Path $Item)){
+            if(-not $AddedFiles.ContainsKey($File)){
+                $MergeFiles += $File
+                $AddedFiles[$File] = $true
+            }
+        }
+    }
+
+    $MergedConfigurationData = $null
+    foreach($File in $MergeFiles){
+        $TemplateData = Import-PowerShellDataFile -Path $File
+        if($null -eq $MergedConfigurationData){
+            $MergedConfigurationData = Copy-ConfigurationDataValue -Value $TemplateData
+            if($MergedConfigurationData -is [System.Collections.IDictionary] -and (Test-ConfigurationDataDictionaryKey -Dictionary $MergedConfigurationData -Key "Metadata")){
+                $MergedConfigurationData.Remove("Metadata")
+            }
+        }else{
+            $MergedConfigurationData = Merge-DSCConfigurationData -Template $MergedConfigurationData -Deployment $TemplateData
+            if($MergedConfigurationData -is [System.Collections.IDictionary] -and (Test-ConfigurationDataDictionaryKey -Dictionary $MergedConfigurationData -Key "Metadata")){
+                $MergedConfigurationData.Remove("Metadata")
+            }
+        }
+    }
+
+    if($PassThru){
+        return [PSCustomObject]@{
+            Files = $MergeFiles
+            ConfigurationData = $MergedConfigurationData
+        }
+    }
+
+    return $MergedConfigurationData
+}

Private/Resolve-ConfigurationDataTemplatePath.ps1

@@ -0,0 +1,24 @@
+function Resolve-ConfigurationDataTemplatePath {
+    [CmdletBinding()]
+    Param(
+        [Parameter(Mandatory=$true)]
+        [string]
+        $Path,
+
+        [Parameter(Mandatory=$false)]
+        [string]
+        $BasePath = (Get-Location).Path
+    )
+
+    $CandidatePath = $Path
+    if(-not [System.IO.Path]::IsPathRooted($CandidatePath)){
+        $CandidatePath = Join-Path -Path $BasePath -ChildPath $CandidatePath
+    }
+
+    $ResolvedPath = Resolve-Path -Path $CandidatePath -ErrorAction SilentlyContinue
+    if($null -eq $ResolvedPath){
+        throw "Configuration data template [$Path] was not found. Base path [$BasePath]."
+    }
+
+    return $ResolvedPath.ProviderPath
+}

Private/Test-ConfigurationDataDictionaryKey.ps1

@@ -0,0 +1,18 @@
+function Test-ConfigurationDataDictionaryKey {
+    [CmdletBinding()]
+    Param(
+        [Parameter(Mandatory=$true)]
+        [System.Collections.IDictionary]
+        $Dictionary,
+
+        [Parameter(Mandatory=$true)]
+        [string]
+        $Key
+    )
+
+    if($Dictionary -is [System.Collections.Specialized.OrderedDictionary]){
+        return $Dictionary.Contains($Key)
+    }
+
+    return $Dictionary.ContainsKey($Key)
+}

Public/Merge-DSCConfigurationData.ps1

@@ -1,47 +1,65 @@
 function Merge-DSCConfigurationData {
-    [CmdletBinding()]
+    [CmdletBinding(DefaultParameterSetName="Data")]
     Param(
-        [Parameter(Mandatory=$true)]
-        [System.Collections.Hashtable]
+        [Parameter(Mandatory=$true, ParameterSetName="Data")]
+        [System.Collections.IDictionary]
         $Template,
-        [Parameter(Mandatory=$false)]
-        [System.Collections.Hashtable]
+
+        [Parameter(Mandatory=$false, ParameterSetName="Data")]
+        [System.Collections.IDictionary]
         $Deployment = @{},
-        [Parameter(Mandatory=$false)]
-        [System.Collections.Hashtable]
-        $Output
+
+        [Parameter(Mandatory=$false, ParameterSetName="Data")]
+        [System.Collections.IDictionary]
+        $Output,
+
+        [Parameter(Mandatory=$true, ParameterSetName="Path", ValueFromPipeline=$true, ValueFromPipelineByPropertyName=$true)]
+        [Alias("FullName")]
+        [string[]]
+        $Path,
+
+        [Parameter(Mandatory=$false, ParameterSetName="Path")]
+        [switch]
+        $PassThru
     )
 
+    begin {
+        $TemplatePath = @()
+    }
+
+    process {
+        if($PSCmdlet.ParameterSetName -eq "Path"){
+            $TemplatePath += @($Path)
+            return
+        }
+
         if($Output -eq $null){
             $Output = $Deployment
         }
 
         foreach($Property in $Template.GetEnumerator()){
-        if($Property.Value -is [System.Collections.Hashtable]){
-            Write-Verbose "Key [$($Property.Name)] is a Hashtable"
-            if($null -ne $Deployment.$($Property.Name)){
-                Write-Verbose "Key [$($Property.Name)] is present in Deployment Data"
-                $Output.($Property.Name) = Merge-DSCConfigurationData -Template $Template.$($Property.Name) -Deployment $Deployment.$($Property.Name) -Output $Output.$($Property.Name)
-            }else{
-                Write-Verbose "Key [$($Property.Name)] is not present in Deployment Data"
-                $Output.Add($($Property.Name),(Copy-ConfigurationDataValue -Value $Template.$($Property.Name)))
+            if($Property.Name -eq "Metadata"){
+                Write-Verbose "Skipping metadata block during configuration data merge"
+                continue
             }
-        }elseif($Property.Value -is [System.Collections.Specialized.OrderedDictionary]){
-            Write-Verbose "Key [$($Property.Name)] is a Ordered Dictionary"
-            if($null -ne $Deployment.$($Property.Name)){
+
+            if($Property.Value -is [System.Collections.IDictionary]){
+                Write-Verbose "Key [$($Property.Name)] is a Dictionary"
+                if(Test-ConfigurationDataDictionaryKey -Dictionary $Deployment -Key $Property.Name){
                     Write-Verbose "Key [$($Property.Name)] is present in Deployment Data"
-                $Output.($Property.Name) = Merge-DSCConfigurationData -Template $Template.$($Property.Name) -Deployment $Deployment.$($Property.Name) -Output $Output.$($Property.Name)
+                    $Output[$Property.Name] = Merge-DSCConfigurationData -Template $Template[$Property.Name] -Deployment $Deployment[$Property.Name] -Output $Output[$Property.Name]
                 }else{
                     Write-Verbose "Key [$($Property.Name)] is not present in Deployment Data"
-                $Output.Add($($Property.Name),(Copy-ConfigurationDataValue -Value $Template.$($Property.Name)))
+                    $Output.Add($Property.Name,(Copy-ConfigurationDataValue -Value $Template[$Property.Name]))
                 }
             }elseif($Property.Value -is [System.Array]){
                 Write-Verbose "$($Property.Name) is ein Array"
                 Write-Verbose "Total Items in Template Array [$($Property.Value.Count)]"
-            Write-Verbose "Total Items in Deployment Array [$($Deployment.$($Property.Name).Count)]"
-            if($null -ne $Deployment.$($Property.Name)){
+                Write-Verbose "Total Items in Deployment Array [$(@(Get-ConfigurationDataDictionaryValue -Dictionary $Deployment -Key $Property.Name -DefaultValue @()).Count)]"
+                if(Test-ConfigurationDataDictionaryKey -Dictionary $Deployment -Key $Property.Name){
                     Write-Verbose "Array is defined in Deployment"
 
+                    $DeploymentArray = Get-ConfigurationDataDictionaryValue -Dictionary $Deployment -Key $Property.Name
                     $TemplateItems = for($i=0;$i -lt $Property.Value.Count; $i++){
                         $SearchKeyNames = @(Get-ConfigurationDataArrayMergeKeyNames -ArrayName $Property.Name -Item $Property.Value[$i])
                         [PSCustomObject]@{
@@ -58,19 +76,19 @@ function Merge-DSCConfigurationData {
 
                         if($SearchKeyNames.Count -eq 0){
                             Write-Verbose "No matching name key found for item in [$($Property.Name)]"
-                        $Output.$($Property.Name) += ,(Copy-ConfigurationDataValue -Value $TemplateItem.Value)
+                            $Output[$Property.Name] += ,(Copy-ConfigurationDataValue -Value $TemplateItem.Value)
                             continue
                         }
 
                         if($TemplateItem.IsWildcard){
-                        $MatchingDeploymentItems = @($Deployment.$($Property.Name) | Where-Object { Test-ConfigurationDataItemHasKeys -Item $_ -KeyNames $SearchKeyNames })
+                            $MatchingDeploymentItems = @($DeploymentArray | Where-Object { Test-ConfigurationDataItemHasKeys -Item $_ -KeyNames $SearchKeyNames })
                         }else{
-                        $MatchingDeploymentItems = @($Deployment.$($Property.Name) | Where-Object { Test-ConfigurationDataItemKeyMatch -Left $_ -Right $TemplateItem.Value -KeyNames $SearchKeyNames })
+                            $MatchingDeploymentItems = @($DeploymentArray | Where-Object { Test-ConfigurationDataItemKeyMatch -Left $_ -Right $TemplateItem.Value -KeyNames $SearchKeyNames })
                         }
 
                         if($MatchingDeploymentItems.Count -gt 0){
                             foreach($DeploymentItem in $MatchingDeploymentItems){
-                            $OutputItem = @($Output.$($Property.Name) | Where-Object { Test-ConfigurationDataItemKeyMatch -Left $_ -Right $DeploymentItem -KeyNames $SearchKeyNames })[0]
+                                $OutputItem = @($Output[$Property.Name] | Where-Object { Test-ConfigurationDataItemKeyMatch -Left $_ -Right $DeploymentItem -KeyNames $SearchKeyNames })[0]
                                 Merge-DSCConfigurationData -Template $TemplateItem.Value -Deployment $DeploymentItem -Output $OutputItem | Out-Null
                             }
                         }else{
@@ -78,21 +96,29 @@ function Merge-DSCConfigurationData {
                                 Write-Verbose "Wildcard item [$(Format-ConfigurationDataMergeKey -Item $TemplateItem.Value -KeyNames $SearchKeyNames)] in [$($Property.Name)] matched no deployment items"
                             }else{
                                 Write-Verbose "Pair [$(Format-ConfigurationDataMergeKey -Item $TemplateItem.Value -KeyNames $SearchKeyNames)] not present"
-                            $Output.$($Property.Name) += ,(Copy-ConfigurationDataValue -Value $TemplateItem.Value)
+                                $Output[$Property.Name] += ,(Copy-ConfigurationDataValue -Value $TemplateItem.Value)
                             }
                         }
                     }
                 }else{
                     Write-Verbose "Array is not defined in Deployment"
-                $Output.$($Property.Name) = Copy-ConfigurationDataValue -Value $Template.$($Property.Name)
+                    $Output[$Property.Name] = Copy-ConfigurationDataValue -Value $Template[$Property.Name]
                 }
             }else{
                 Write-Verbose "$($Property.Name) is a String or Integer Value"
-            if($null -eq $Deployment.$($Property.Name)){
-                $Output.Add($Property.Name,(Copy-ConfigurationDataValue -Value $Template.($Property.Name)))
-            }elseif($Deployment.$($Property.Name) -ne $Property.Value){
+                if(-not (Test-ConfigurationDataDictionaryKey -Dictionary $Deployment -Key $Property.Name)){
+                    $Output.Add($Property.Name,(Copy-ConfigurationDataValue -Value $Template[$Property.Name]))
+                }elseif($Deployment[$Property.Name] -ne $Property.Value){
                 }
             }
         }
+
         return $Output
     }
+
+    end {
+        if($PSCmdlet.ParameterSetName -eq "Path"){
+            return Merge-ConfigurationDataTemplateFile -Path $TemplatePath -PassThru:$PassThru
+        }
+    }
+}

Tests/Extends.Tests.ps1

@@ -0,0 +1,120 @@
+$script:ModuleRoot = Split-Path -Parent $PSScriptRoot
+$script:ModuleManifest = Join-Path -Path $script:ModuleRoot -ChildPath 'Merge-DSCConfigurationData.psd1'
+
+Import-Module $script:ModuleManifest -Force
+
+Describe 'Merge-DSCConfigurationData Extends' {
+    It 'keeps the existing hashtable merge behavior' {
+        $Template = @{
+            Parameters = @{
+                DomainFQDN = @{
+                    Type = 'string'
+                    Required = $true
+                    DefaultValue = 'example.local'
+                }
+            }
+        }
+
+        $Deployment = @{
+            Parameters = @{
+                DomainFQDN = @{
+                    Value = 'contoso.local'
+                }
+            }
+        }
+
+        $Result = Merge-DSCConfigurationData -Template $Template -Deployment $Deployment
+
+        $Result.Parameters.DomainFQDN.Type | Should Be 'string'
+        $Result.Parameters.DomainFQDN.Required | Should Be $true
+        $Result.Parameters.DomainFQDN.Value | Should Be 'contoso.local'
+    }
+
+    It 'merges a child template with Metadata.Extends' {
+        $DefaultPath = Join-Path -Path $TestDrive -ChildPath 'Default.psd1'
+        $ChildPath = Join-Path -Path $TestDrive -ChildPath 'Contoso.psd1'
+
+        @'
+@{
+    Metadata = @{
+        TemplateType = 'Environment'
+        Name = 'Default'
+    }
+    Parameters = @{
+        DomainFQDN = @{
+            Type = 'string'
+            Required = $true
+            DefaultValue = 'example.local'
+        }
+        DomainNetBIOS = @{
+            Type = 'string'
+            Required = $true
+        }
+    }
+    Resources = @{
+        NonNodeData = @{
+            RequiredModules = @(
+                @{
+                    Name = 'ActiveDirectoryDsc'
+                    Version = '6.7.1'
+                }
+            )
+        }
+    }
+}
+'@ | Set-Content -Path $DefaultPath -Encoding UTF8
+
+        @'
+@{
+    Metadata = @{
+        TemplateType = 'Environment'
+        Name = 'Contoso'
+        Extends = './Default.psd1'
+    }
+    Parameters = @{
+        DomainFQDN = @{
+            Value = 'contoso.local'
+        }
+        DomainNetBIOS = @{
+            Value = 'CONTOSO'
+        }
+    }
+}
+'@ | Set-Content -Path $ChildPath -Encoding UTF8
+
+        $Result = Merge-DSCConfigurationData -Path $ChildPath -PassThru
+
+        $Result.Files.Count | Should Be 2
+        [System.IO.Path]::GetFileName($Result.Files[0]) | Should Be 'Default.psd1'
+        [System.IO.Path]::GetFileName($Result.Files[1]) | Should Be 'Contoso.psd1'
+        $Result.ConfigurationData.Parameters.DomainFQDN.Type | Should Be 'string'
+        $Result.ConfigurationData.Parameters.DomainFQDN.Value | Should Be 'contoso.local'
+        $Result.ConfigurationData.Parameters.DomainNetBIOS.Required | Should Be $true
+        $Result.ConfigurationData.Parameters.DomainNetBIOS.Value | Should Be 'CONTOSO'
+        $Result.ConfigurationData.Resources.NonNodeData.RequiredModules[0].Name | Should Be 'ActiveDirectoryDsc'
+        $Result.ConfigurationData.ContainsKey('Metadata') | Should Be $false
+    }
+
+    It 'detects circular Metadata.Extends references' {
+        $APath = Join-Path -Path $TestDrive -ChildPath 'A.psd1'
+        $BPath = Join-Path -Path $TestDrive -ChildPath 'B.psd1'
+
+        @'
+@{
+    Metadata = @{
+        Extends = './B.psd1'
+    }
+}
+'@ | Set-Content -Path $APath -Encoding UTF8
+
+        @'
+@{
+    Metadata = @{
+        Extends = './A.psd1'
+    }
+}
+'@ | Set-Content -Path $BPath -Encoding UTF8
+
+        { Merge-DSCConfigurationData -Path $APath } | Should Throw
+    }
+}