Frontend: Refactor how flags are saved for module interfaces.

There are two axes on which a saved frontend flag can be categorized for
printing in a `.swiftinterface` file:

1. Whether the flag is "ignorable" or not.
2. Which levels of interface the flag should be in (public, package).

This refactor ensures that those two axes are modeled independently and
prepares the infrastructure to allow flags to appear in the private and package
interfaces without being included in the public interface.

Author: tshortli

include/swift/Frontend/ModuleInterfaceSupport.h

@@ -41,19 +41,22 @@ struct ModuleInterfaceOptions {
   /// [TODO: Clang-type-plumbing] This check should go away.
   bool PrintFullConvention = false;
 
-  /// Copy of all the command-line flags passed at .swiftinterface
-  /// generation time, re-applied to CompilerInvocation when reading
-  /// back .swiftinterface and reconstructing .swiftmodule.
-  std::string Flags;
-
-  /// Keep track of flags to be printed in package.swiftinterface only.
-  /// If -disable-print-package-name-for-non-package-interface is passed,
-  /// package-name flag should only be printed in package.swiftinterface.
-  std::string FlagsForPackageOnly;
-
-  /// Flags that should be emitted to the .swiftinterface file but are OK to be
-  /// ignored by the earlier version of the compiler.
-  std::string IgnorableFlags;
+  struct InterfaceFlags {
+    /// Copy of all the command-line flags passed at .swiftinterface
+    /// generation time, re-applied to CompilerInvocation when reading
+    /// back .swiftinterface and reconstructing .swiftmodule.
+    std::string Flags = "";
+
+    /// Flags that should be emitted to the .swiftinterface file but are OK to
+    /// be ignored by the earlier version of the compiler.
+    std::string IgnorableFlags = "";
+  };
+
+  /// Flags which appear in all .swiftinterface files.
+  InterfaceFlags PublicFlags = {};
+
+  /// Flags which appear only in the .package.swiftinterface.
+  InterfaceFlags PackageFlags = {};
 
   /// Print imports with both @_implementationOnly and @_spi, only applies
   /// when PrintSPIs is true.

lib/Frontend/CompilerInvocation.cpp

@@ -435,6 +435,10 @@ static void ParseModuleInterfaceArgs(ModuleInterfaceOptions &Opts,
 /// Checks if an arg is generally allowed to be included
 /// in a module interface
 static bool ShouldIncludeModuleInterfaceArg(const Arg *A) {
+  if (!A->getOption().hasFlag(options::ModuleInterfaceOption) &&
+      !A->getOption().hasFlag(options::ModuleInterfaceOptionIgnorable))
+    return false;
+
   if (!A->getOption().matches(options::OPT_enable_experimental_feature))
     return true;
 
@@ -459,43 +463,47 @@ static void SaveModuleInterfaceArgs(ModuleInterfaceOptions &Opts,
                                     ArgList &Args, DiagnosticEngine &Diags) {
   if (!FOpts.InputsAndOutputs.hasModuleInterfaceOutputPath())
     return;
-  
-  ArgStringList RenderedArgs;
-  ArgStringList RenderedArgsForPackageOnly;
-  ArgStringList RenderedArgsIgnorable;
+
+  struct RenderedInterfaceArgs {
+    ArgStringList Standard = {};
+    ArgStringList Ignorable = {};
+  };
+
+  RenderedInterfaceArgs PublicArgs{};
+  RenderedInterfaceArgs PackageArgs{};
+
+  auto interfaceArgListForArg = [&](Arg *A) -> ArgStringList & {
+    bool ignorable =
+        A->getOption().hasFlag(options::ModuleInterfaceOptionIgnorable);
+    if (ShouldIncludeArgInPackageInterfaceOnly(A, Args))
+      return ignorable ? PackageArgs.Ignorable : PackageArgs.Standard;
+
+    return ignorable ? PublicArgs.Ignorable : PublicArgs.Standard;
+  };
 
   for (auto A : Args) {
     if (!ShouldIncludeModuleInterfaceArg(A))
       continue;
 
-    if (A->getOption().hasFlag(options::ModuleInterfaceOptionIgnorable)) {
-      A->render(Args, RenderedArgsIgnorable);
-    } else if (A->getOption().hasFlag(options::ModuleInterfaceOption)) {
-      if (ShouldIncludeArgInPackageInterfaceOnly(A, Args))
-        A->render(Args, RenderedArgsForPackageOnly);
-      else
-        A->render(Args, RenderedArgs);
-    }
-  }
-  {
-    llvm::raw_string_ostream OS(Opts.Flags);
-    interleave(RenderedArgs,
-               [&](const char *Argument) { PrintArg(OS, Argument, StringRef()); },
-               [&] { OS << " "; });
-  }
-  {
-    llvm::raw_string_ostream OS(Opts.FlagsForPackageOnly);
-    interleave(
-        RenderedArgsForPackageOnly,
-        [&](const char *Argument) { PrintArg(OS, Argument, StringRef()); },
-        [&] { OS << " "; });
-  }
-  {
-    llvm::raw_string_ostream OS(Opts.IgnorableFlags);
-    interleave(RenderedArgsIgnorable,
-               [&](const char *Argument) { PrintArg(OS, Argument, StringRef()); },
-               [&] { OS << " "; });
-  }
+    ArgStringList &ArgList = interfaceArgListForArg(A);
+    A->render(Args, ArgList);
+  }
+
+  auto updateInterfaceOpts = [](ModuleInterfaceOptions::InterfaceFlags &Flags,
+                                RenderedInterfaceArgs &RenderedArgs) {
+    auto printFlags = [](std::string &str, ArgStringList argList) {
+      llvm::raw_string_ostream OS(str);
+      interleave(
+          argList,
+          [&](const char *Argument) { PrintArg(OS, Argument, StringRef()); },
+          [&] { OS << " "; });
+    };
+    printFlags(Flags.Flags, RenderedArgs.Standard);
+    printFlags(Flags.IgnorableFlags, RenderedArgs.Ignorable);
+  };
+
+  updateInterfaceOpts(Opts.PublicFlags, PublicArgs);
+  updateInterfaceOpts(Opts.PackageFlags, PackageArgs);
 }
 
 enum class CxxCompatMode {

lib/Frontend/ModuleInterfaceSupport.cpp

@@ -59,15 +59,12 @@ static void printToolVersionAndFlagsComment(raw_ostream &out,
       << InterfaceFormatVersion << "\n";
   out << "// " SWIFT_COMPILER_VERSION_KEY ": "
       << ToolsVersion << "\n";
-  out << "// " SWIFT_MODULE_FLAGS_KEY ": "
-      << Opts.Flags;
+  out << "// " SWIFT_MODULE_FLAGS_KEY ": " << Opts.PublicFlags.Flags;
 
-  // Adding package-name can be disabled in non-package
-  // swiftinterfaces; add only to package.swiftinterface
-  // in such case.
-  if (Opts.printPackageInterface() &&
-      !Opts.FlagsForPackageOnly.empty())
-    out << " " << Opts.FlagsForPackageOnly;
+  // Append flags that are for the package interface only (e.g. -package-name
+  // when -disable-print-package-name-for-non-package-interface is specified).
+  if (Opts.printPackageInterface() && !Opts.PackageFlags.Flags.empty())
+    out << " " << Opts.PackageFlags.Flags;
 
   // Insert additional -module-alias flags
   if (Opts.AliasModuleNames) {
@@ -103,10 +100,14 @@ static void printToolVersionAndFlagsComment(raw_ostream &out,
   }
   out << "\n";
 
-  if (!Opts.IgnorableFlags.empty()) {
+  if (!Opts.PublicFlags.IgnorableFlags.empty()) {
     out << "// " SWIFT_MODULE_FLAGS_IGNORABLE_KEY ": "
-        << Opts.IgnorableFlags << "\n";
+        << Opts.PublicFlags.IgnorableFlags << "\n";
   }
+
+  // Append ignorable flags that are for the package interface only.
+  if (Opts.printPackageInterface() && !Opts.PackageFlags.IgnorableFlags.empty())
+    out << " " << Opts.PackageFlags.IgnorableFlags;
 }
 
 std::string