[ExplicitModule] Support direct cc1 flag for all explicit module build jobs

Update swift-driver to support directly instantiate clang importer in
all jobs with cc1 flags. In the new mode, swift dependency scanner will
return all the cc1 flags to the actual compilation doesn't need to run
clang driver again. In this mode, swift-driver should avoid forwarding
Xcc command-line options since those are expected to be clang driver
args, not cc1 args.

Author: cachemeifyoucan

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -101,6 +101,17 @@ extension Driver {
       jobNeedPathRemap = false
     }
 
+    // Check if dependency scanner has put the job into direct clang cc1 mode.
+    // If dependency scanner put us into direct cc1 mode, avoid adding `-Xcc` options, since
+    // dependency scanner already adds needed flags and -Xcc options known by swift-driver are
+    // clang driver flags but not it requires cc1 flags.
+    let directModuleCC1Mode = commandLine.contains(Job.ArgTemplate.flag("-direct-clang-cc1-module-build"))
+    func appendXccFlag(_ flag: String) {
+      guard !directModuleCC1Mode else { return }
+      commandLine.appendFlag(.Xcc)
+      commandLine.appendFlag(flag)
+    }
+
     if let variant = parsedOptions.getLastArgument(.targetVariant)?.asSingle {
       commandLine.appendFlag(.targetVariant)
       commandLine.appendFlag(Triple(variant, normalizing: true).triple)
@@ -125,8 +136,7 @@ extension Driver {
     try commandLine.appendLast(.enableExperimentalCxxInterop, from: &parsedOptions)
     try commandLine.appendLast(.cxxInteroperabilityMode, from: &parsedOptions)
     if let stdlibVariant = parsedOptions.getLastArgument(.experimentalCxxStdlib)?.asSingle {
-      commandLine.appendFlag("-Xcc")
-      commandLine.appendFlag("-stdlib=\(stdlibVariant)")
+      appendXccFlag("-stdlib=\(stdlibVariant)")
     }
 
     if isEmbeddedEnabled && parsedOptions.hasArgument(.enableLibraryEvolution) {
@@ -173,8 +183,7 @@ extension Driver {
     try commandLine.appendAll(.vfsoverlay, from: &parsedOptions)
 
     if let gccToolchain = parsedOptions.getLastArgument(.gccToolchain) {
-        commandLine.appendFlag(.Xcc)
-        commandLine.appendFlag("--gcc-toolchain=\(gccToolchain.asSingle)")
+        appendXccFlag("--gcc-toolchain=\(gccToolchain.asSingle)")
     }
 
     try commandLine.appendLast(.AssertConfig, from: &parsedOptions)
@@ -272,6 +281,11 @@ extension Driver {
     if isFrontendArgSupported(.strictConcurrency) {
       try commandLine.appendLast(.strictConcurrency, from: &parsedOptions)
     }
+    if kind == .scanDependencies,
+        isFrontendArgSupported(.experimentalClangImporterDirectCc1Scan) {
+      try commandLine.appendAll(
+        .experimentalClangImporterDirectCc1Scan, from: &parsedOptions)
+    }
 
     // Expand the -experimental-hermetic-seal-at-link flag
     if parsedOptions.hasArgument(.experimentalHermeticSealAtLink) {
@@ -332,7 +346,7 @@ extension Driver {
       try commandLine.appendLast(.disableSandbox, from: &parsedOptions)
     }
 
-    if !(isCachingEnabled && useClangIncludeTree), let workingDirectory = workingDirectory {
+    if !directModuleCC1Mode, let workingDirectory = workingDirectory {
       // Add -Xcc -working-directory before any other -Xcc options to ensure it is
       // overridden by an explicit -Xcc -working-directory, although having a
       // different working directory is probably incorrect.
@@ -394,8 +408,8 @@ extension Driver {
     // Pass through any subsystem flags.
     try commandLine.appendAll(.Xllvm, from: &parsedOptions)
 
-    // If using clang-include-tree, `-Xcc` should only be passed to scanDependencies job.
-    if (kind == .scanDependencies) || !(isCachingEnabled && useClangIncludeTree) {
+    // Pass through all -Xcc flags if not under directModuleCC1Mode.
+    if !directModuleCC1Mode {
       try commandLine.appendAll(.Xcc, from: &parsedOptions)
     }