Suffix temporary directory with unique path

Fixes #529

Reusing the temporary directory can cause issues with concurrent
instances of Danger. By appending a unique identifier we can prevent
race conditions when running Danger from concurrent processes.

Author: squarefrog

CHANGELOG.md

@@ -14,6 +14,7 @@
 ## Master
 
 - Drop Swift 5.3 support [@417-72KI][] - [#524](https://github.com/danger/swift/pull/524)
+- Refine runner temporary path to better support concurrent pipelines [@squarefrog][] - [#530](https://github.com/danger/swift/pull/530)
 
 ## 3.13.0
 

Sources/Runner/Commands/Runner.swift

@@ -9,9 +9,14 @@ func runDanger(logger: Logger) throws {
     // Pull in the JSON from Danger JS
     let standardInput = FileHandle.standardInput
     let fileManager = FileManager.default
-    let tmpPath = NSTemporaryDirectory()
+    let tmpPath = NSTemporaryDirectory() + "danger/\(UUID().uuidString)/"
     let dangerResponsePath = tmpPath + "danger-response.json"
 
+    try fileManager.createDirectory(
+        at: URL(fileURLWithPath: tmpPath),
+        withIntermediateDirectories: true
+    )
+
     // Pull in the JSON from Danger JS
     guard let dangerDSLURL = String(data: standardInput.readDataToEndOfFile(), encoding: .utf8) else {
         logger.logError("Could get the Dangerfile DSL URL from STDing")