A PowerShell script that can be used in a VSTS Build to get a filtered list of file changes and have those files copied to the Staging directory.

FileChangesForRelease.ps1

#
# FileChangesForRelease.ps1
#
# Gets the list of .rdl files that were added or modified since the previous commit (based on the PR) and copies them to the staging directory
#

$urlBase = $env:SYSTEM_TEAMFOUNDATIONSERVERURI + $env:SYSTEM_TEAMPROJECT + "/_apis/";
$accessToken = $env:SYSTEM_ACCESSTOKEN;
$auth = "Bearer $accessToken";
$accept = "application/json";
$headers = @{authorization=$auth;accept=$accept};

# Call the API to get the commit changes object of the lastMergeCommit which is the source of this build
$commitChangesUrl = $urlBase + "git/repositories/" + $env:BUILD_REPOSITORY_NAME + "/commits/" + $env:BUILD_SOURCEVERSION + "/changes?api-version=1.0";
$commitChanges = Invoke-RestMethod -Uri $commitChangesUrl -Method Get -Headers $headers -ContentType "application/json";

# Enumerate the $commitChanges.changes array and filter down -> blobs -> only the added/modified .rdl files -> "select/foreach" into an array of paths
[string[]]$rdlFilePaths = $commitChanges.changes `
	| Where-Object {$_.item.gitObjectType -eq "blob" -and $_.item.path.EndsWith(".rdl") -and ($_.changeType -eq "edit" -or $_.changeType -eq "add" -or $_.changeType -eq "edit, rename")} `
	| Select-Object item `
	| ForEach-Object {$_.item.path};
Write-Host "rdlFilePaths are: $rdlFilePaths";

# Enumerate the array of paths and copy each file into the staging directory under a sub-folder called release package
for($i=0; $i -lt $rdlFilePaths.Length; $i++){
	[string]$pathItem = [string]$rdlFilePaths[$i];
	Write-Host "Iteration $i || The pathItem is $pathItem";

	# Get the file name and replace all spaces with dashes to make it more path friendly
	[int]$fileIndex = $pathItem.LastIndexOf('/');
	[string]$fileName = $pathItem.Substring($fileIndex + 1);
	$fileName = $fileName.Replace(' ', '-').Trim();

	# Replace all the forward slashes (/) with back slashes (\) because Windows
	$pathInstance = $env:BUILD_SOURCESDIRECTORY + $pathItem.Replace("/", "\");
	Write-Host "Iteration $i || The Path Instance: $pathInstance";

	# Establish the destination file name and path
	$destination = $env:BUILD_STAGINGDIRECTORY + "\release-package\" + $fileName;
	Write-Host "Iteration $i || The Destination staging directory is: $destination";

	# If the desitnation doesn't exist create it
	if(!(Test-Path -Path $destination)) {New-Item $destination};

	# Makin' Copies!
	Copy-Item "$pathInstance" -Destination "$destination" -Force;
}