Stage in frontend flags for experimental cross-module incremental builds

Author: CodaFi

include/swift/Frontend/FrontendOptions.h

@@ -276,6 +276,14 @@ class FrontendOptions {
   /// of the main Swift module's source files.
   bool ImportPrescan = false;
 
+  /// When performing an incremental build, ensure that cross-module incremental
+  /// build metadata is available in any swift modules emitted by this frontend
+  /// job.
+  ///
+  /// This flag is currently only propagated from the driver to
+  /// any merge-modules jobs.
+  bool EnableExperimentalCrossModuleIncrementalBuild = false;
+
   /// The different modes for validating TBD against the LLVM IR.
   enum class TBDValidationMode {
     Default,        ///< Do the default validation for the current platform.

include/swift/Serialization/SerializationOptions.h

@@ -131,6 +131,7 @@ namespace swift {
     bool SerializeAllSIL = false;
     bool SerializeOptionsForDebugging = false;
     bool IsSIB = false;
+    bool ExperimentalCrossModuleIncrementalInfo = false;
   };
 
 } // end namespace swift

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -92,6 +92,9 @@ bool ArgsToFrontendOptionsConverter::convert(
 
   Opts.ImportPrescan |= Args.hasArg(OPT_import_prescan);
 
+  Opts.EnableExperimentalCrossModuleIncrementalBuild |=
+      Args.hasArg(OPT_enable_experimental_cross_module_incremental_build);
+
   // Always track system dependencies when scanning dependencies.
   if (const Arg *ModeArg = Args.getLastArg(OPT_modes_Group)) {
     if (ModeArg->getOption().matches(OPT_scan_dependencies)) {

lib/Frontend/Frontend.cpp

@@ -175,6 +175,9 @@ SerializationOptions CompilerInvocation::computeSerializationOptions(
       opts.SerializeOptionsForDebugging.getValueOr(
           !isModuleExternallyConsumed(module));
 
+  serializationOpts.ExperimentalCrossModuleIncrementalInfo =
+      opts.EnableExperimentalCrossModuleIncrementalBuild;
+
   return serializationOpts;
 }
 

test/Driver/cross_module.swift

@@ -0,0 +1,6 @@
+// RUN: %empty-directory(%t/sub)
+// RUN: echo "{\"\": {\"swift-dependencies\": \"cross_module.swiftdeps\"}}" > %t/ofm.json
+// RUN: %swiftc_driver -incremental -emit-module -module-name cross_module -output-file-map=%/t/ofm.json -driver-print-jobs -target x86_64-apple-macosx10.9 %s -enable-experimental-cross-module-incremental-build 2>^1 | %FileCheck -check-prefix ENABLE %s
+
+// ENABLE: {{bin(/|\\\\)swift(-frontend|c)?(\.exe)?"?}} -frontend -merge-modules
+// ENABLE-SAME: -enable-experimental-cross-module-incremental-build