Explicitely disable cache for SwiftLintPlugin runs on Xcode Cloud (#5287

)

In Xcode Cloud environment, SwiftLint’s cache cannot be written. When using the SwiftLintPlugin, there is no way to disable the cache. Previously, a solution was made for the SwiftLint CLI itself where it looks at a set of environment variables (#4485). This solution offers a cleaner approach where the plugin itself decides whether it needs to enable or disable the cache based on the `CI_XCODE_CLOUD` environment variable.

In the long run, SwiftLint should get rid of `isLikelyXcodeCloudEnvironment` entirely. The caller should always decide if caching is possible or not, while SwiftLint itself should be platform-agnostic.

Plugins/SwiftLintPlugin/SwiftLintPlugin.swift

@@ -32,10 +32,17 @@ struct SwiftLintPlugin: BuildToolPlugin {
             // We always pass all of the Swift source files in the target to the tool,
             // so we need to ensure that any exclusion rules in the configuration are
             // respected.
-            "--force-exclude",
-            "--cache-path", "\(workingDirectory)"
+            "--force-exclude"
         ]
 
+        // Determine whether we need to enable cache or not (for Xcode Cloud we don't)
+        if ProcessInfo.processInfo.environment["CI_XCODE_CLOUD"] == "TRUE" {
+            arguments.append("--no-cache")
+        } else {
+            arguments.append("--cache-path")
+            arguments.append("\(workingDirectory)")
+        }
+
         // Manually look for configuration files, to avoid issues when the plugin does not execute our tool from the
         // package source directory.
         if let configuration = packageDirectory.firstConfigurationFileInParentDirectories() {