[CAS] For compilation tasks, add an unintrusive cache hit/miss indicator

This goes in the task's output, so in the Xcode build log the user would have to expand the task output to see such detail.

Author: akyrtzi

Sources/SWBTaskExecution/TaskActions/ClangCompileTaskAction.swift

@@ -373,6 +373,7 @@ public final class ClangCompileTaskAction: TaskAction, BuildValueValidatingTaskA
             }
             outputDelegate.incrementClangCacheMiss()
             outputDelegate.incrementTaskCounter(.cacheMisses)
+            outputDelegate.emitOutput("Cache miss\n")
             return false
         }
 
@@ -385,6 +386,7 @@ public final class ClangCompileTaskAction: TaskAction, BuildValueValidatingTaskA
                 }
                 outputDelegate.incrementClangCacheMiss()
                 outputDelegate.incrementTaskCounter(.cacheMisses)
+                outputDelegate.emitOutput("Cache miss\n")
                 return false
             }
         }
@@ -397,6 +399,7 @@ public final class ClangCompileTaskAction: TaskAction, BuildValueValidatingTaskA
         }
         outputDelegate.incrementClangCacheHit()
         outputDelegate.incrementTaskCounter(.cacheHits)
+        outputDelegate.emitOutput("Cache hit\n")
         outputDelegate.emitOutput(ByteString(encodingAsUTF8: diagnosticText))
         return true
     }

Sources/SWBTaskExecution/TaskActions/SwiftDriverJobTaskAction.swift

@@ -647,9 +647,11 @@ public final class SwiftDriverJobTaskAction: TaskAction, BuildValueValidatingTas
         if result {
             outputDelegate.incrementSwiftCacheHit()
             outputDelegate.incrementTaskCounter(.cacheHits)
+            outputDelegate.emitOutput("Cache hit\n")
         } else {
             outputDelegate.incrementSwiftCacheMiss()
             outputDelegate.incrementTaskCounter(.cacheMisses)
+            outputDelegate.emitOutput("Cache miss\n")
         }
         return result
     }

Tests/SWBBuildSystemTests/ClangCompilationCachingTests.swift

@@ -1842,6 +1842,7 @@ extension BuildOperationTester.BuildResults {
             Issue.record("Unable to find cache miss diagnostic for task \(task)", sourceLocation: sourceLocation)
             return
         }
+        check(contains: .taskHadEvent(task, event: .hadOutput(contents: "Cache miss\n")), sourceLocation: sourceLocation)
     }
 
     fileprivate func checkCompileCacheHit(_ task: Task, sourceLocation: SourceLocation = #_sourceLocation) {
@@ -1851,5 +1852,6 @@ extension BuildOperationTester.BuildResults {
             return
         }
         while getDiagnosticMessageForTask(.contains("using CAS output"), kind: .note, task: task) != nil {}
+        check(contains: .taskHadEvent(task, event: .hadOutput(contents: "Cache hit\n")), sourceLocation: sourceLocation)
     }
 }

Tests/SWBBuildSystemTests/SwiftCompilationCachingTests.swift

@@ -96,6 +96,7 @@ fileprivate struct SwiftCompilationCachingTests: CoreBasedTests {
                 results.checkTask(.matchTargetName("Application"), .matchRule(["SwiftCompile", "normal", "arm64", "Compiling App.swift", "\(tmpDirPath.str)/Test/aProject/App.swift"])) { task in
                     task.checkCommandLineMatches([.suffix("swift-frontend"), .anySequence, "-cache-compile-job", .anySequence])
                     numCompile += 1
+                    results.checkKeyQueryCacheMiss(task)
                 }
                 results.checkTask(.matchTargetName("Application"), .matchRule(["SwiftEmitModule", "normal", "arm64", "Emitting module for Application"])) { _ in }
 
@@ -121,6 +122,10 @@ fileprivate struct SwiftCompilationCachingTests: CoreBasedTests {
 
             tester.userInfo = rawUserInfo.withAdditionalEnvironment(environment: metricsEnv("two"))
             try await tester.checkBuild(runDestination: .anyiOSDevice, persistent: true) { results in
+                results.checkTask(.matchRule(["SwiftCompile", "normal", "arm64", "Compiling App.swift", "\(tmpDirPath.str)/Test/aProject/App.swift"])) { task in
+                    results.checkKeyQueryCacheHit(task)
+                }
+
                 results.checkNote("4 hits (100%), 0 misses")
             }
             #expect(try readMetrics("two").contains("\"swiftCacheHits\":\(numCompile),\"swiftCacheMisses\":0"))
@@ -206,6 +211,7 @@ extension BuildOperationTester.BuildResults {
             Issue.record("Unable to find cache miss diagnostic for task \(task)", sourceLocation: sourceLocation)
             return
         }
+        check(contains: .taskHadEvent(task, event: .hadOutput(contents: "Cache miss\n")), sourceLocation: sourceLocation)
     }
 
     fileprivate func checkKeyQueryCacheHit(_ task: Task, sourceLocation: SourceLocation = #_sourceLocation) {
@@ -214,5 +220,6 @@ extension BuildOperationTester.BuildResults {
             Issue.record("Unable to find cache hit diagnostic for task \(task)", sourceLocation: sourceLocation)
             return
         }
+        check(contains: .taskHadEvent(task, event: .hadOutput(contents: "Cache hit\n")), sourceLocation: sourceLocation)
     }
 }