[Preview] Fix preview support for swift caching build (#562)

cachemeifyoucan · web-flow · commit 6c6309e4b37a · 2025-06-12T07:53:51.000-07:00
Add support for swift caching build when swift compiler supports the new
option that allows swift compiler performs an uncached build but loading
module dependencies from CAS.

It also does few adjustment to make sure preview build shares the same
dependencies with regular build as caching build has a stricter rule for
invalidation:

* The VFS overlay used by preview is applied after swift driver
  invocation and onto the frontend invocation directly. This makes sure
  the VFS overlay doesn't invalidate all the module dependencies.
* BridgingHeader PCH was disabled as a workaround when swift driver
  doesn't produce deterministic output path when planning for PCH jobs.
  Properly fix this issue by requesting the same path when planning both
  build and don't use this workaround in certain configurations.

This should allow preview to build thunk correctly when swift caching is
enabled for the regular build.

rdar://152107465
diff --git a/Sources/SWBCore/SpecImplementations/Tools/SwiftCompiler.swift b/Sources/SWBCore/SpecImplementations/Tools/SwiftCompiler.swift
@@ -337,6 +337,7 @@ public struct SwiftDriverPayload: Serializable, TaskPayload, Encodable {
     public let uniqueID: String
     public let compilerLocation: LibSwiftDriver.CompilerLocation
     public let moduleName: String
+    public let outputPrefix: String
     public let tempDirPath: Path
     public let explicitModulesTempDirPath: Path
     public let variant: String
@@ -352,10 +353,11 @@ public struct SwiftDriverPayload: Serializable, TaskPayload, Encodable {
     public let dependencyFilteringRootPath: Path?
     public let verifyScannerDependencies: Bool
 
-    internal init(uniqueID: String, compilerLocation: LibSwiftDriver.CompilerLocation, moduleName: String, tempDirPath: Path, explicitModulesTempDirPath: Path, variant: String, architecture: String, eagerCompilationEnabled: Bool, explicitModulesEnabled: Bool, commandLine: [String], ruleInfo: [String], isUsingWholeModuleOptimization: Bool, casOptions: CASOptions?, reportRequiredTargetDependencies: BooleanWarningLevel, linkerResponseFilePath: Path?, dependencyFilteringRootPath: Path?, verifyScannerDependencies: Bool) {
+    internal init(uniqueID: String, compilerLocation: LibSwiftDriver.CompilerLocation, moduleName: String, outputPrefix: String, tempDirPath: Path, explicitModulesTempDirPath: Path, variant: String, architecture: String, eagerCompilationEnabled: Bool, explicitModulesEnabled: Bool, commandLine: [String], ruleInfo: [String], isUsingWholeModuleOptimization: Bool, casOptions: CASOptions?, reportRequiredTargetDependencies: BooleanWarningLevel, linkerResponseFilePath: Path?, dependencyFilteringRootPath: Path?, verifyScannerDependencies: Bool) {
         self.uniqueID = uniqueID
         self.compilerLocation = compilerLocation
         self.moduleName = moduleName
+        self.outputPrefix = outputPrefix
         self.tempDirPath = tempDirPath
         self.explicitModulesTempDirPath = explicitModulesTempDirPath
         self.variant = variant
@@ -373,10 +375,11 @@ public struct SwiftDriverPayload: Serializable, TaskPayload, Encodable {
     }
 
     public init(from deserializer: any Deserializer) throws {
-        try deserializer.beginAggregate(17)
+        try deserializer.beginAggregate(18)
         self.uniqueID = try deserializer.deserialize()
         self.compilerLocation = try deserializer.deserialize()
         self.moduleName = try deserializer.deserialize()
+        self.outputPrefix = try deserializer.deserialize()
         self.tempDirPath = try deserializer.deserialize()
         self.explicitModulesTempDirPath = try deserializer.deserialize()
         self.variant = try deserializer.deserialize()
@@ -394,10 +397,11 @@ public struct SwiftDriverPayload: Serializable, TaskPayload, Encodable {
     }
 
     public func serialize<T>(to serializer: T) where T : Serializer {
-        serializer.serializeAggregate(17) {
+        serializer.serializeAggregate(18) {
             serializer.serialize(self.uniqueID)
             serializer.serialize(self.compilerLocation)
             serializer.serialize(self.moduleName)
+            serializer.serialize(self.outputPrefix)
             serializer.serialize(self.tempDirPath)
             serializer.serialize(self.explicitModulesTempDirPath)
             serializer.serialize(self.variant)
@@ -2502,7 +2506,7 @@ public final class SwiftCompilerSpec : CompilerSpec, SpecIdentifierType, SwiftDi
             let explicitModuleBuildEnabled = await swiftExplicitModuleBuildEnabled(cbc.producer, cbc.scope, delegate)
             let verifyScannerDependencies = explicitModuleBuildEnabled && cbc.scope.evaluate(BuiltinMacros.SWIFT_DEPENDENCY_REGISTRATION_MODE) == .verifySwiftDependencyScanner
 
-            return SwiftDriverPayload(uniqueID: uniqueID, compilerLocation: compilerLocation, moduleName: scope.evaluate(BuiltinMacros.SWIFT_MODULE_NAME), tempDirPath: tempDirPath, explicitModulesTempDirPath: explicitModulesTempDirPath, variant: variant, architecture: arch, eagerCompilationEnabled: eagerCompilationEnabled(args: args, scope: scope, compilationMode: compilationMode, isUsingWholeModuleOptimization: isUsingWholeModuleOptimization), explicitModulesEnabled: explicitModuleBuildEnabled, commandLine: commandLine, ruleInfo: ruleInfo, isUsingWholeModuleOptimization: isUsingWholeModuleOptimization, casOptions: casOptions, reportRequiredTargetDependencies: scope.evaluate(BuiltinMacros.DIAGNOSE_MISSING_TARGET_DEPENDENCIES), linkerResponseFilePath: linkerResponseFilePath, dependencyFilteringRootPath: cbc.producer.sdk?.path, verifyScannerDependencies: verifyScannerDependencies)
+            return SwiftDriverPayload(uniqueID: uniqueID, compilerLocation: compilerLocation, moduleName: scope.evaluate(BuiltinMacros.SWIFT_MODULE_NAME), outputPrefix: scope.evaluate(BuiltinMacros.TARGET_NAME) + compilationMode.moduleBaseNameSuffix, tempDirPath: tempDirPath, explicitModulesTempDirPath: explicitModulesTempDirPath, variant: variant, architecture: arch, eagerCompilationEnabled: eagerCompilationEnabled(args: args, scope: scope, compilationMode: compilationMode, isUsingWholeModuleOptimization: isUsingWholeModuleOptimization), explicitModulesEnabled: explicitModuleBuildEnabled, commandLine: commandLine, ruleInfo: ruleInfo, isUsingWholeModuleOptimization: isUsingWholeModuleOptimization, casOptions: casOptions, reportRequiredTargetDependencies: scope.evaluate(BuiltinMacros.DIAGNOSE_MISSING_TARGET_DEPENDENCIES), linkerResponseFilePath: linkerResponseFilePath, dependencyFilteringRootPath: cbc.producer.sdk?.path, verifyScannerDependencies: verifyScannerDependencies)
         }
 
         func constructSwiftResponseFileTask(path: Path) {
@@ -3397,10 +3401,12 @@ public final class SwiftCompilerSpec : CompilerSpec, SpecIdentifierType, SwiftDi
             removeWithParameter(arg)
         }
 
-        // We need to ignore precompiled headers due to:
+        // For some old version of swift driver, the output path for bridging header pch is not stable,
+        // we need to disable bridging header pch when caching or bridging header chaining is not enabled as a workaround:
         // rdar://126212044 ([JIT] iOS test Failures: Thunk build failure, unable to read PCH file)
-        removeWithPrefix("-cache-compile-job")
-        commandLine.append("-disable-bridging-pch")
+        if !commandLine.contains("-cache-compile-job") || !commandLine.contains("-auto-bridging-header-chaining") {
+            commandLine.append("-disable-bridging-pch")
+        }
 
         if payload.previewStyle == .dynamicReplacement {
             for (arg, newValue) in [
@@ -3440,6 +3446,7 @@ public final class SwiftCompilerSpec : CompilerSpec, SpecIdentifierType, SwiftDi
         }
 
         let selectedInputPath: Path
+        let newVFSOverlayPath: Path?
         if payload.previewStyle == .xojit {
             // Also pass the auxiliary Swift files.
             commandLine.append(contentsOf: originalInputs.map(\.str))
@@ -3448,7 +3455,8 @@ public final class SwiftCompilerSpec : CompilerSpec, SpecIdentifierType, SwiftDi
             if let driverPayload = payload.driverPayload {
                 do {
                     // Inject the thunk source into the output file map
-                    let map = SwiftOutputFileMap(files: [sourceFile.str: .init(object: outputPath.str)])
+                    let pchPath = driverPayload.tempDirPath.join(driverPayload.outputPrefix + "-primary-Bridging-header.pch")
+                    let map = SwiftOutputFileMap(files: [sourceFile.str: .init(object: outputPath.str), "": .init(pch: pchPath.str)])
                     let newOutputFileMap = driverPayload.tempDirPath.join(UUID().uuidString)
                     try fs.createDirectory(newOutputFileMap.dirname, recursive: true)
                     try fs.write(newOutputFileMap, contents: ByteString(JSONEncoder(outputFormatting: [.prettyPrinted, .sortedKeys, .withoutEscapingSlashes]).encode(map)))
@@ -3457,19 +3465,20 @@ public final class SwiftCompilerSpec : CompilerSpec, SpecIdentifierType, SwiftDi
                     // rdar://127735418 ([JIT] Emit a vfsoverlay for JIT preview thunk compiler arguments so clients can specify the original file path when substituting contents)
                     let vfs = VFS()
                     vfs.addMapping(sourceFile, externalContents: inputPath)
-                    let newVFSOverlayPath = driverPayload.tempDirPath.join("vfsoverlay-\(inputPath.basename).json")
+                    newVFSOverlayPath = driverPayload.tempDirPath.join("vfsoverlay-\(inputPath.basename).json")
                     try fs.createDirectory(newOutputFileMap.dirname, recursive: true)
                     let overlay = try vfs.toVFSOverlay().propertyListItem.asJSONFragment().asString
-                    try fs.write(newVFSOverlayPath, contents: ByteString(encodingAsUTF8: overlay))
-
-                    commandLine.append(contentsOf: ["-vfsoverlay", newVFSOverlayPath.str])
+                    try fs.write(newVFSOverlayPath!, contents: ByteString(encodingAsUTF8: overlay))
                 } catch {
                     return []
                 }
+            } else {
+                newVFSOverlayPath = nil
             }
         }
         else {
             selectedInputPath = inputPath
+            newVFSOverlayPath = nil
             commandLine.append(contentsOf: [inputPath.str])
         }
 
@@ -3516,6 +3525,21 @@ public final class SwiftCompilerSpec : CompilerSpec, SpecIdentifierType, SwiftDi
                 casOptions: driverPayload.casOptions
             ) {
                 commandLine = newCommandLine
+                // For swift caching jobs, add extra flags.
+                if commandLine.contains("-cache-compile-job") {
+                    // Ideally, we should ask if swift-frontend supports the flag but we can only ask driver for an approximation.
+                    if LibSwiftDriver.supportsDriverFlag(spelled: "-module-import-from-cas") {
+                        commandLine.append("-module-import-from-cas")
+                    }
+                    // Then drop the cache build flag to do uncached preview compilation.
+                    commandLine.removeAll {
+                        $0 == "-cache-compile-job"
+                    }
+                }
+                // Add vfsoverlay after the driver invocation as it can affect the module dependencies, causing modules from regular builds not being reused here.
+                if let vfsOverlay = newVFSOverlayPath {
+                    commandLine.append(contentsOf: ["-vfsoverlay", vfsOverlay.str])
+                }
             } else {
                 commandLine = []
             }
diff --git a/Tests/SWBBuildSystemTests/PreviewsBuildOperationTests.swift b/Tests/SWBBuildSystemTests/PreviewsBuildOperationTests.swift
@@ -227,8 +227,6 @@ fileprivate struct PreviewsBuildOperationTests: CoreBasedTests {
                                 "\(srcRoot.str)/build/Debug-iphonesimulator",
                                 "-F",
                                 "\(srcRoot.str)/build/Debug-iphonesimulator",
-                                "-vfsoverlay",
-                                "\(srcRoot.str)/build/ProjectName.build/Debug-iphonesimulator/AppTarget.build/Objects-normal/\(results.runDestinationTargetArchitecture)/vfsoverlay-main.selection.preview-thunk.swift.json",
                                 "-no-color-diagnostics",
                                 "-g",
                                 "-debug-info-format=dwarf",
@@ -278,7 +276,9 @@ fileprivate struct PreviewsBuildOperationTests: CoreBasedTests {
                                 "-target-sdk-name",
                                 "iphonesimulator\(core.loadSDK(.iOSSimulator).defaultDeploymentTarget)",
                                 "-o",
-                                "\(srcRoot.str)/build/ProjectName.build/Debug-iphonesimulator/AppTarget.build/Objects-normal/\(results.runDestinationTargetArchitecture)/main.selection.preview-thunk.o"
+                                "\(srcRoot.str)/build/ProjectName.build/Debug-iphonesimulator/AppTarget.build/Objects-normal/\(results.runDestinationTargetArchitecture)/main.selection.preview-thunk.o",
+                                "-vfsoverlay",
+                                "\(srcRoot.str)/build/ProjectName.build/Debug-iphonesimulator/AppTarget.build/Objects-normal/\(results.runDestinationTargetArchitecture)/vfsoverlay-main.selection.preview-thunk.swift.json",
                             ]
                         )
                         #expect(previewInfo.thunkInfo?.thunkSourceFile == Path("\(srcRoot.str)/build/ProjectName.build/Debug-iphonesimulator/AppTarget.build/Objects-normal/\(results.runDestinationTargetArchitecture)/main.selection.preview-thunk.swift"))
@@ -531,8 +531,6 @@ fileprivate struct PreviewsBuildOperationTests: CoreBasedTests {
                                 "\(srcRoot.str)/build/Debug-iphonesimulator",
                                 "-F",
                                 "\(srcRoot.str)/build/Debug-iphonesimulator",
-                                "-vfsoverlay",
-                                "\(srcRoot.str)/build/ProjectName.build/Debug-iphonesimulator/AppTarget.build/Objects-normal/\(results.runDestinationTargetArchitecture)/vfsoverlay-File1.selection.preview-thunk.swift.json",
                                 "-no-color-diagnostics",
                                 "-g",
                                 "-debug-info-format=dwarf",
@@ -582,7 +580,9 @@ fileprivate struct PreviewsBuildOperationTests: CoreBasedTests {
                                 "-target-sdk-name",
                                 "iphonesimulator\(core.loadSDK(.iOSSimulator).defaultDeploymentTarget)",
                                 "-o",
-                                "\(srcRoot.str)/build/ProjectName.build/Debug-iphonesimulator/AppTarget.build/Objects-normal/\(results.runDestinationTargetArchitecture)/File1.selection.preview-thunk.o"
+                                "\(srcRoot.str)/build/ProjectName.build/Debug-iphonesimulator/AppTarget.build/Objects-normal/\(results.runDestinationTargetArchitecture)/File1.selection.preview-thunk.o",
+                                "-vfsoverlay",
+                                "\(srcRoot.str)/build/ProjectName.build/Debug-iphonesimulator/AppTarget.build/Objects-normal/\(results.runDestinationTargetArchitecture)/vfsoverlay-File1.selection.preview-thunk.swift.json",
                             ]
                         )
                         #expect(previewInfo.thunkInfo?.thunkSourceFile == Path("\(srcRoot.str)/build/ProjectName.build/Debug-iphonesimulator/AppTarget.build/Objects-normal/\(results.runDestinationTargetArchitecture)/File1.selection.preview-thunk.swift"))
diff --git a/Tests/SwiftBuildTests/GeneratePreviewInfoTests.swift b/Tests/SwiftBuildTests/GeneratePreviewInfoTests.swift
@@ -160,14 +160,13 @@ fileprivate struct GeneratePreviewInfoTests: CoreBasedTests {
                         .anySequence,
                         "-sdk", "\(sdkroot)",
                         .anySequence,
-                        "-vfsoverlay", "\(tmpDir.str)/Test/build/Test.build/Debug-iphoneos/App.build/Objects-normal/\(activeRunDestination.targetArchitecture)/vfsoverlay-TestFile4.canary.preview-thunk.swift.json",
-                        .anySequence,
                         "-Onone",
                         .anySequence,
                         "-module-name", "App",
                         "-target-sdk-version", "\(deploymentTarget)",
                         "-target-sdk-name", "iphoneos\(deploymentTarget)",
                         "-o", "\(tmpDir.str)/Test/build/Test.build/Debug-iphoneos/App.build/Objects-normal/\(activeRunDestination.targetArchitecture)/TestFile4.canary.preview-thunk.o",
+                        "-vfsoverlay", "\(tmpDir.str)/Test/build/Test.build/Debug-iphoneos/App.build/Objects-normal/\(activeRunDestination.targetArchitecture)/vfsoverlay-TestFile4.canary.preview-thunk.swift.json",
                         .end
                     ])
                     // Also spot-check that some options which were removed in SwiftCompilerSpec.generatePreviewInfo() for XOJIT are not present.
