Import XML files using the encoding of the XML declaration (if specified) using XmlReader and XmlDocument

ImportXmlCommand.ps1

function Import-Xml {
	[CmdletBinding(DefaultParameterSetName='Path')]
	param(
		[Parameter(ParameterSetName='Path', Mandatory=$true, Position=0, ValueFromPipeline=$true, ValueFromPipelineByPropertyName=$true)]
		[ValidateNotNullOrEmpty()]
		[string[]]
		$Path,

		[Parameter(ParameterSetName='LiteralPath', Mandatory=$true, ValueFromPipelineByPropertyName=$true)]
		[Alias('PSPath', 'LP')]
		[ValidateNotNullOrEmpty()]
		[string[]]
		$LiteralPath,

		[Parameter()]
		[System.Xml.XmlReaderSettings]
		$Settings,

		[Parameter()]
		[switch]
		$PreserveWhitespace
	)

	begin {
		if (-not $PSBoundParameters.ContainsKey('Settings')) {
			$Settings = [System.Xml.XmlReaderSettings]::new()
		}
	}

	process {
		[string[]]$xmlFilePaths = if ($null -ne $LiteralPath) {
			# ensures proper paths
			Microsoft.PowerShell.Management\Resolve-Path -LiteralPath $LiteralPath
		} else {
			# expand paths with wildcard characters
			Microsoft.PowerShell.Management\Resolve-Path -Path $Path
		}

		#! To check streaming:
		# https://docs.microsoft.com/en-us/dotnet/standard/linq/stream-xml-fragments-xmlreader
		# https://docs.microsoft.com/en-us/dotnet/standard/linq/linq-xml-vs-xml-technologies
		foreach ($xmlFilePath in $xmlFilePaths) {
			try {
				$xmlReader                      = [System.Xml.XmlReader]::Create($xmlFilePath, $Settings)
				$xmlDocument                    = [System.Xml.XmlDocument]::new()
				$xmlDocument.PreserveWhitespace = $PreserveWhitespace
				$xmlDocument.Load($xmlReader)
				$xmlDocument
			} catch {
				# add some details to exception. ErrorDetails take automatically precedence for 'ToString()'
				$errorDetails = '["{0}"] {1}' -f $xmlFilePath, $_.ToString()
				$_.ErrorDetails = [System.Management.Automation.ErrorDetails]::new($errorDetails)

				# re-throw exception
				Write-Error -ErrorRecord $_
			} finally {
				$xmlReader.Close()
				$xmlReader.Dispose()
			}
		}
	}
}