[Frontend] Add -swift-compiler-version option to frontend, module interfaces

This option is going to be used to indicate what compiler was used
to build swift interface/module which is required for SE-0438.

Author: xedin

include/swift/Basic/Version.h

@@ -187,6 +187,10 @@ StringRef getCurrentCompilerChannel();
 /// users.
 unsigned getUpcomingCxxInteropCompatVersion();
 
+/// Retrieves the version of the running compiler. It could be a tag or
+/// a "development" version that only has major/minor.
+std::string getCompilerVersion();
+
 } // end namespace version
 } // end namespace swift
 

include/swift/Frontend/FrontendOptions.h

@@ -110,6 +110,10 @@ class FrontendOptions {
   /// User-defined module version number.
   llvm::VersionTuple UserModuleVersion;
 
+  /// The Swift compiler version number that would be used to synthesize
+  /// swiftinterface files and subsequently swiftmodules.
+  llvm::VersionTuple SwiftCompilerVersion;
+
   /// A set of modules allowed to import this module.
   std::set<std::string> AllowableClients;
 

include/swift/Option/Options.td

@@ -303,6 +303,11 @@ def package_description_version: Separate<["-"], "package-description-version">,
   HelpText<"The version number to be applied on the input for the PackageDescription availability kind">,
   MetaVarName<"<vers>">;
 
+def swift_compiler_version : Separate<["-"], "swift-compiler-version">,
+  Flags<[FrontendOption, HelpHidden, ModuleInterfaceOptionIgnorable]>,
+  HelpText<"The version of the Swift compiler used to emit swift interface and module">,
+  MetaVarName<"<compvers>">;
+
 def tools_directory : Separate<["-"], "tools-directory">,
   Flags<[FrontendOption, NoInteractiveOption, DoesNotAffectIncrementalBuild,
          ArgumentIsPath]>,

lib/Basic/Version.cpp

@@ -339,5 +339,18 @@ unsigned getUpcomingCxxInteropCompatVersion() {
   return SWIFT_VERSION_MAJOR + 1;
 }
 
+std::string getCompilerVersion() {
+  std::string buf;
+  llvm::raw_string_ostream OS(buf);
+
+#if defined(SWIFT_COMPILER_VERSION)
+  OS << SWIFT_COMPILER_VERSION;
+#else
+  OS << SWIFT_VERSION_STRING;
+#endif
+
+  return OS.str();
+}
+
 } // end namespace version
 } // end namespace swift

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -299,6 +299,15 @@ bool ArgsToFrontendOptionsConverter::convert(
   if (const Arg *A = Args.getLastArg(OPT_public_module_name))
     Opts.PublicModuleName = A->getValue();
 
+  if (auto A = Args.getLastArg(OPT_swift_compiler_version)) {
+    if (Opts.SwiftCompilerVersion.tryParse(A->getValue())) {
+      Diags.diagnose(SourceLoc(), diag::error_invalid_arg_value,
+                     A->getAsString(Args), A->getValue());
+    }
+  } else {
+    Opts.SwiftCompilerVersion.tryParse(version::getCompilerVersion());
+  }
+
   // This must be called after computing module name, module abi name,
   // and module link name. If computing module aliases is unsuccessful,
   // return early.