Add subsetDescriptor to completion message

If we build just a specific product or target, add a `subsetDescriptor` to the complete message. This improves the confusing output when plugins are using executables, because we end up with multiple 'Build complete' messages.

Author: neonichu

Sources/Build/BuildOperation.swift

@@ -286,7 +286,21 @@ public final class BuildOperation: PackageStructureDelegate, SPMBuildCore.BuildS
 
         let duration = buildStartTime.distance(to: .now())
 
-        self.buildSystemDelegate?.buildComplete(success: success, duration: duration)
+        let subsetDescriptor: String?
+        switch subset {
+        case .product(let productName):
+            subsetDescriptor = "product '\(productName)'"
+        case .target(let targetName):
+            subsetDescriptor = "target: '\(targetName)'"
+        case .allExcludingTests, .allIncludingTests:
+            subsetDescriptor = nil
+        }
+
+        self.buildSystemDelegate?.buildComplete(
+            success: success,
+            duration: duration,
+            subsetDescriptor: subsetDescriptor
+        )
         self.delegate?.buildSystem(self, didFinishWithResult: success)
         guard success else { throw Diagnostics.fatalError }
 

Sources/Build/BuildOperationBuildSystemDelegateHandler.swift

@@ -956,11 +956,18 @@ final class BuildOperationBuildSystemDelegateHandler: LLBuildBuildSystemDelegate
         }
     }
 
-    func buildComplete(success: Bool, duration: DispatchTimeInterval) {
+    func buildComplete(success: Bool, duration: DispatchTimeInterval, subsetDescriptor: String? = nil) {
+        let subsetString: String
+        if let subsetDescriptor {
+            subsetString = "of \(subsetDescriptor) "
+        } else {
+            subsetString = ""
+        }
+
         queue.sync {
             self.progressAnimation.complete(success: success)
             if success {
-                let message = cancelled ? "Build cancelled!" : "Build complete!"
+                let message = cancelled ? "Build \(subsetString)cancelled!" : "Build \(subsetString)complete!"
                 self.progressAnimation.clear()
                 self.outputStream.send("\(message) (\(duration.descriptionInSeconds))\n")
                 self.outputStream.flush()