Add an optional language feature for Library Evolution

Replace the one-off compiler flag for Library Evolution with an
optional language feature. This makes the
`hasFeature(LibraryEvolution)` check work in an `#if`, and is
otherwise just cleanup.

Tracked by rdar://161125572.

include/swift/Basic/Features.def

@@ -308,6 +308,8 @@ UPCOMING_FEATURE(ImmutableWeakCaptures, 481, 7)
 /// safety.
 MIGRATABLE_OPTIONAL_LANGUAGE_FEATURE(StrictMemorySafety, 458, "Strict memory safety")
 
+OPTIONAL_LANGUAGE_FEATURE(LibraryEvolution, 0, "Library evolution")
+
 // Experimental features
 
 EXPERIMENTAL_FEATURE(StaticAssert, false)

include/swift/Frontend/FrontendOptions.h

@@ -298,11 +298,6 @@ public:
   /// \see ModuleDecl::isImplicitDynamicEnabled
   bool EnableImplicitDynamic = false;
 
-  /// Enables the "fully resilient" resilience strategy.
-  ///
-  /// \see ResilienceStrategy::Resilient
-  bool EnableLibraryEvolution = false;
-
   /// If set, this module is part of a mixed Objective-C/Swift framework, and
   /// the Objective-C half should implicitly be visible to the Swift sources.
   bool ImportUnderlyingModule = false;

include/swift/Sema/SourceLoader.h

@@ -25,20 +25,16 @@ class SourceLoader : public ModuleLoader {
 private:
   ASTContext &Ctx;
   std::vector<ModuleDecl *> ModulesToBindExtensions;
-  bool EnableLibraryEvolution;
 
   explicit SourceLoader(ASTContext &ctx,
-                        bool enableResilience,
                         DependencyTracker *tracker)
-    : ModuleLoader(tracker), Ctx(ctx),
-      EnableLibraryEvolution(enableResilience) {}
+    : ModuleLoader(tracker), Ctx(ctx) {}
 
 public:
   static std::unique_ptr<SourceLoader>
-  create(ASTContext &ctx, bool enableResilience,
-         DependencyTracker *tracker = nullptr) {
+  create(ASTContext &ctx, DependencyTracker *tracker = nullptr) {
     return std::unique_ptr<SourceLoader>{
-      new SourceLoader(ctx, enableResilience, tracker)
+      new SourceLoader(ctx, tracker)
     };
   }
 

lib/AST/FeatureSet.cpp

@@ -327,6 +327,7 @@ static bool usesFeatureCDecl(Decl *decl) {
 }
 
 UNINTERESTING_FEATURE(StrictMemorySafety)
+UNINTERESTING_FEATURE(LibraryEvolution)
 UNINTERESTING_FEATURE(SafeInteropWrappers)
 UNINTERESTING_FEATURE(AssumeResilientCxxTypes)
 UNINTERESTING_FEATURE(ImportNonPublicCxxMembers)

lib/Basic/SupportedFeatures.cpp

@@ -59,6 +59,9 @@ static std::optional<std::string_view> optionalFlagName(Feature feature) {
   case Feature::StrictMemorySafety:
     return "-strict-memory-safety";
 
+  case Feature::LibraryEvolution:
+    return "-enable-library-evolution";
+
 #define LANGUAGE_FEATURE(FeatureName, SENumber, Description) case Feature::FeatureName:
 #define OPTIONAL_LANGUAGE_FEATURE(FeatureName, SENumber, Description)
 #include "swift/Basic/Features.def"

lib/DriverTool/sil_opt_main.cpp

@@ -704,8 +704,8 @@ int sil_opt_main(ArrayRef<const char *> argv, void *MainAddr) {
     Invocation.setTargetTriple(options.Target);
   if (!options.ResourceDir.empty())
     Invocation.setRuntimeResourcePath(options.ResourceDir);
-  Invocation.getFrontendOptions().EnableLibraryEvolution
-    = options.EnableLibraryEvolution;
+  if (options.EnableLibraryEvolution)
+    Invocation.getLangOptions().enableFeature(Feature::LibraryEvolution);
   Invocation.getFrontendOptions().StrictImplicitModuleContext
     = options.StrictImplicitModuleContext;
 

lib/DriverTool/swift_symbolgraph_extract_main.cpp

@@ -140,7 +140,7 @@ int swift_symbolgraph_extract_main(ArrayRef<const char *> Args,
   Invocation.getLangOptions().EnableObjCInterop = Target.isOSDarwin();
   Invocation.getLangOptions().DebuggerSupport = true;
 
-  Invocation.getFrontendOptions().EnableLibraryEvolution = true;
+  Invocation.getLangOptions().enableFeature(Feature::LibraryEvolution);
 
   std::string ModuleCachePath = "";
   if (auto *A = ParsedArgs.getLastArg(OPT_module_cache_path)) {

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -107,16 +107,12 @@ bool ArgsToFrontendOptionsConverter::convert(
 
   Opts.EnableTesting |= Args.hasArg(OPT_enable_testing);
   Opts.EnablePrivateImports |= Args.hasArg(OPT_enable_private_imports);
-  Opts.EnableLibraryEvolution |= Args.hasArg(OPT_enable_library_evolution);
   Opts.FrontendParseableOutput |= Args.hasArg(OPT_frontend_parseable_output);
   Opts.ExplicitInterfaceBuild |= Args.hasArg(OPT_explicit_interface_module_build);
 
   Opts.EmitClangHeaderWithNonModularIncludes |=
       Args.hasArg(OPT_emit_clang_header_nonmodular_includes);
 
-  // FIXME: Remove this flag
-  Opts.EnableLibraryEvolution |= Args.hasArg(OPT_enable_resilience);
-
   Opts.EnableImplicitDynamic |= Args.hasArg(OPT_enable_implicit_dynamic);
 
   if (Args.hasArg(OPT_track_system_dependencies)) {

lib/Frontend/CompilerInvocation.cpp

@@ -1011,6 +1011,9 @@ static bool ParseEnabledFeatureArgs(LangOptions &Opts, ArgList &Args,
   else if (Args.hasArg(OPT_strict_memory_safety_migrate))
     Opts.enableFeature(Feature::StrictMemorySafety, /*forMigration=*/true);
 
+  if (Args.hasArg(OPT_enable_library_evolution, OPT_enable_resilience))
+    Opts.enableFeature(Feature::LibraryEvolution);
+
   return HadError;
 }
 
@@ -1799,7 +1802,7 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
       HadError = true;
     }
 
-    if (FrontendOpts.EnableLibraryEvolution) {
+    if (Opts.hasFeature(Feature::LibraryEvolution)) {
       Diags.diagnose(SourceLoc(), diag::evolution_with_embedded);
       HadError = true;
     }
@@ -2131,7 +2134,8 @@ static bool ParseClangImporterArgs(ClangImporterOptions &Opts, ArgList &Args,
 
   // Until we have some checking in place, internal bridging headers are a
   // bit unsafe without library evolution.
-  if (Opts.BridgingHeaderIsInternal && !FrontendOpts.EnableLibraryEvolution) {
+  if (Opts.BridgingHeaderIsInternal &&
+      !LangOpts.hasFeature(Feature::LibraryEvolution)) {
     Diags.diagnose(SourceLoc(),
                    diag::internal_bridging_header_without_library_evolution);
   }
@@ -3068,7 +3072,7 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
           FrontendOptions::ActionType::TypecheckModuleFromInterface)
         Diags.diagnose(SourceLoc(), diag::ignoring_option_requires_option,
                        "-package-cmo", "-allow-non-resilient-access");
-    } else if (!FEOpts.EnableLibraryEvolution) {
+    } else if (!LangOpts.hasFeature(Feature::LibraryEvolution)) {
       Diags.diagnose(SourceLoc(), diag::package_cmo_requires_library_evolution);
     } else {
       Opts.EnableSerializePackage = true;

lib/Frontend/Frontend.cpp

@@ -813,10 +813,7 @@ bool CompilerInstance::setUpModuleLoaders() {
   }
 
   if (hasSourceImport()) {
-    bool enableLibraryEvolution =
-      Invocation.getFrontendOptions().EnableLibraryEvolution;
     Context->addModuleLoader(SourceLoader::create(*Context,
-                                                  enableLibraryEvolution,
                                                   getDependencyTracker()));
   }
 
@@ -1173,7 +1170,7 @@ bool CompilerInvocation::shouldImportCxx() const {
   if (getFrontendOptions().ModuleName == CXX_MODULE_NAME)
     return false;
   // Cxx cannot be imported when Library evolution is enabled
-  if (getFrontendOptions().EnableLibraryEvolution)
+  if (getLangOptions().hasFeature(Feature::LibraryEvolution))
     return false;
   // Implicit import of Cxx is disabled
   if (getLangOptions().DisableImplicitCxxModuleImport)
@@ -1507,7 +1504,7 @@ ModuleDecl *CompilerInstance::getMainModule() const {
       MainModule->setPublicModuleName(getASTContext().getIdentifier(
           Invocation.getFrontendOptions().PublicModuleName));
     }
-    if (Invocation.getFrontendOptions().EnableLibraryEvolution)
+    if (Invocation.getLangOptions().hasFeature(Feature::LibraryEvolution))
       MainModule->setResilienceStrategy(ResilienceStrategy::Resilient);
     if (Invocation.getLangOptions().isSwiftVersionAtLeast(6))
       MainModule->setIsConcurrencyChecked(true);

lib/Sema/SourceLoader.cpp

@@ -139,7 +139,7 @@ ModuleDecl *SourceLoader::loadModule(SourceLoc importLoc,
     addFile(new (Ctx) SourceFile(*importMod, SourceFileKind::Library, bufferID,
                                  opts));
   });
-  if (EnableLibraryEvolution)
+  if (Ctx.LangOpts.hasFeature(Feature::LibraryEvolution))
     importMod->setResilienceStrategy(ResilienceStrategy::Resilient);
   Ctx.addLoadedModule(importMod);
   Ctx.bumpGeneration();

test/Parse/library_evolution_feature.swift

@@ -0,0 +1,6 @@
+// RUN: %target-typecheck-verify-swift -enable-library-evolution
+
+#if hasFeature(LibraryEvolution)
+#else
+#error("Missing feature")
+#endif