Function for adding new package source mappings to nuget.config files. (#411)

* Function for adding new package source mappings to nuget.config files.

* Defaulting to `$PWD` for relative paths

* Array of patterns, so we save once.
Package source mapping section presence check.

Author: agr

build/common.ps1

@@ -955,4 +955,34 @@ Function Remove-EditorconfigFile() {
     # See https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/configuration-files#severity-options
     Remove-Item $editorconfigFilePath
     Trace-Log "Removed $editorconfigFilePath"
+}
+
+Function Add-PackageSourceMapping(
+    [Parameter(Mandatory=$True)][string]$NuGetConfigPath,
+    [Parameter(Mandatory=$True)][string]$SourceKey,
+    [Parameter(Mandatory=$True)][string[]]$Patterns) {
+    if (-not [System.IO.Path]::IsPathRooted($NuGetConfigPath)) {
+        $NuGetConfigPath = Join-Path $PWD $NuGetConfigPath
+    }
+
+    $config = [xml](Get-Content -Raw $NuGetConfigPath)
+    if (-not $config.configuration.packageSourceMapping) {
+        Write-Host "No package source mapping section. Not doing anything."
+        return
+    }
+
+    $packageSourceNode = $config.configuration.packageSourceMapping.packageSource | Where-Object { $_.key -eq $SourceKey }
+    if (-not $packageSourceNode) {
+        $packageSourceNode = $config.CreateElement("packageSource")
+        $packageSourceNode.SetAttribute("key", $SourceKey)
+        $config.configuration.packageSourceMapping.AppendChild($packageSourceNode) | Out-Null
+    }
+
+    foreach ($pattern in $Patterns)
+    {
+        $package = $config.CreateElement("package")
+        $package.SetAttribute("pattern", $pattern)
+        $packageSourceNode.AppendChild($package) | Out-Null
+    }
+    $config.Save($NuGetConfigPath)
 }