[TEST-ONLY] Try renable compilation caching tests

Sources/SWBTestSupport/SkippedTestSupport.swift

@@ -175,6 +175,10 @@ extension Trait where Self == Testing.ConditionTrait {
         return .skipIfEnvironmentVariableSet(key: "GITHUB_ACTIONS")
     }
 
+    package static func skipInXcodeCloud(_ comment: Comment? = nil) -> Self {
+        return .skipIfEnvironmentVariableSet(key: "CI_XCODE_CLOUD")
+    }
+
     package static func requireClangFeatures(_ requiredFeatures: DiscoveredClangToolSpecInfo.FeatureFlag...) -> Self {
         enabled("Clang compiler does not support features: \(requiredFeatures)") {
             let features = try await ConditionTraitContext.shared.clangFeatures
@@ -295,7 +299,10 @@ extension Trait where Self == Testing.ConditionTrait {
     /// Constructs a condition trait that causes a test to be disabled if not running against a version of Xcode within the given range.
     package static func requireXcodeBuildVersions<R: RangeExpression>(in range: @Sendable @autoclosure @escaping () throws -> R, sourceLocation: SourceLocation = #_sourceLocation) -> Self where R.Bound == ProductBuildVersion {
         enabled("Xcode version is not suitable", sourceLocation: sourceLocation, {
-            return try await range().contains(InstalledXcode.currentlySelected().productBuildVersion())
+            guard let installedVersion =  try? await InstalledXcode.currentlySelected().productBuildVersion() else {
+                return true
+            }
+            return try range().contains(installedVersion)
         })
     }
 

Tests/SWBBuildSystemTests/ClangCompilationCachingTests.swift

@@ -19,8 +19,7 @@ import SWBTestSupport
 import SWBUtil
 
 @Suite(.skipHostOS(.windows, "Windows platform has no CAS support yet"),
-       .requireDependencyScannerPlusCaching,
-       .flaky("A handful of Swift Build CAS tests fail when running the entire test suite"), .bug("rdar://146781403"))
+       .requireDependencyScannerPlusCaching, .skipInXcodeCloud("flaky tests"), .requireXcode26())
 fileprivate struct ClangCompilationCachingTests: CoreBasedTests {
     let canUseCASPlugin: Bool
     let canUseCASPruning: Bool
@@ -1580,7 +1579,7 @@ fileprivate struct ClangCompilationCachingTests: CoreBasedTests {
             func checkModuleCommandLine(task: Task, results: BuildOperationTester.BuildResults, name: String) {
                 // The final command-line is only known to the dynamic task, but it's printed to output so we can check that.
                 results.checkTaskOutput(task) { output in
-                    XCTAssertMatch(output.stringValue, .contains(#"\#(name)\=/\^mod"#))
+                    XCTAssertMatch(output.stringValue, .or(.contains(#"\#(name)\=/\^mod"#), .contains(#"\#(name) /\^mod"#)))
                     checkCommandLineCommon(output: output)
                 }
             }
@@ -1843,6 +1842,7 @@ fileprivate struct ClangCompilationCachingTests: CoreBasedTests {
                 "CLANG_ENABLE_COMPILE_CACHE": enableCaching ? "YES" : "NO",
                 "CLANG_ENABLE_MODULES": "NO",
                 "COMPILATION_CACHE_CAS_PATH": casPath.str,
+                "DSTROOT": tmpDirPath.join("dstroot").str,
             ]
             if usePlugin {
                 buildSettings["COMPILATION_CACHE_ENABLE_PLUGIN"] = "YES"
@@ -1967,7 +1967,11 @@ fileprivate struct ClangCompilationCachingTests: CoreBasedTests {
             // Ignore output for plugin CAS since it may not yet support validation.
             try await checkBuild("validated successfully\n")
             // Create an error and trigger revalidation by messing with the validation data.
-            try tester.fs.move(casPath.join("builtin/v1.1/v8.data"), to: casPath.join("builtin/v1.1/v8.data.moved"))
+            let dataDir = casPath.join("builtin").join("v1.1")
+            let dataFile = try #require(tester.fs.listdir(dataDir).first {
+                $0.hasSuffix(".data") && $0.hasPrefix("v")
+            })
+            try tester.fs.move(dataDir.join(dataFile), to: dataDir.join("moved"))
             try await tester.fs.writeFileContents(casPath.join("builtin/v1.validation")) { stream in
                 stream <<< "0"
             }

Tests/SWBBuildSystemTests/ClangModuleVerifierTests.swift

@@ -192,7 +192,7 @@ fileprivate struct ClangModuleVerifierTests: CoreBasedTests {
     }
 
     @Test(.requireSDKs(.macOS), .requireClangFeatures(.wSystemHeadersInModule), .requireDependencyScannerPlusCaching,
-          .flaky("A handful of Swift Build CAS tests fail when running the entire test suite"), .bug("rdar://146781403"))
+          .skipInXcodeCloud("flaky tests"), .requireXcode26())
     func cachedBuild() async throws {
         try await withTemporaryDirectory { (tmpDirPath: Path) in
             let archs = ["arm64", "x86_64"]

Tests/SWBBuildSystemTests/SwiftCompilationCachingTests.swift

@@ -20,7 +20,7 @@ import SWBTaskExecution
 import SWBProtocol
 
 @Suite(.requireSwiftFeatures(.compilationCaching),
-       .flaky("A handful of Swift Build CAS tests fail when running the entire test suite"), .bug("rdar://146781403"))
+       .skipInXcodeCloud("flaky tests"), .requireXcode26())
 fileprivate struct SwiftCompilationCachingTests: CoreBasedTests {
     @Test(.requireSDKs(.iOS))
     func swiftCachingSimple() async throws {