Add -enable-experimental-feature X for experimental features.

include/swift/AST/DiagnosticsFrontend.def

@@ -36,6 +36,10 @@ ERROR(error_unsupported_target_os, none,
 ERROR(error_unsupported_target_arch, none,
       "unsupported target architecture: '%0'", (StringRef))
 
+ERROR(error_experimental_feature_not_available, none,
+      "experimental feature '%0' cannot be enabled in a production compiler",
+      (StringRef))
+
 ERROR(error_unknown_library_level, none,
       "unknown library level '%0', "
       "expected one of 'api', 'spi' or 'other'", (StringRef))

include/swift/Basic/Feature.h

@@ -18,18 +18,18 @@
 namespace swift {
 
 class LangOptions;
-  
+
 /// Enumeration describing all of the named features.
 enum class Feature {
 #define LANGUAGE_FEATURE(FeatureName, SENumber, Description, Option) \
-  FeatureName,
-  #include "swift/Basic/Features.def"
+FeatureName,
+#include "swift/Basic/Features.def"
 };
 
 constexpr unsigned numFeatures() {
   enum Features {
 #define LANGUAGE_FEATURE(FeatureName, SENumber, Description, Option) \
-    FeatureName,
+FeatureName,
 #include "swift/Basic/Features.def"
     NumFeatures
   };
@@ -51,6 +51,10 @@ inline bool featureImpliesFeature(Feature feature, Feature implied) {
   return (unsigned) feature < (unsigned) implied;
 }
 
+/// Get the feature corresponding to this "experimental" feature, if there is
+/// one.
+llvm::Optional<Feature> getExperimentalFeature(llvm::StringRef name);
+
 }
 
 #endif // SWIFT_BASIC_FEATURES_H

include/swift/Basic/Features.def

@@ -48,7 +48,12 @@
   LANGUAGE_FEATURE(FeatureName, SENumber, Description, Option)
 #endif
 
-LANGUAGE_FEATURE(StaticAssert, 0, "#assert", langOpts.EnableExperimentalStaticAssert)
+#ifndef EXPERIMENTAL_FEATURE
+#  define EXPERIMENTAL_FEATURE(FeatureName)  \
+     LANGUAGE_FEATURE(FeatureName, 0, #FeatureName, \
+                      langOpts.hasFeature(#FeatureName))
+#endif
+
 LANGUAGE_FEATURE(AsyncAwait, 296, "async/await", true)
 LANGUAGE_FEATURE(EffectfulProp, 310, "Effectful properties", true)
 LANGUAGE_FEATURE(MarkerProtocol, 0, "@_marker protocol", true)
@@ -78,5 +83,14 @@ SUPPRESSIBLE_LANGUAGE_FEATURE(PrimaryAssociatedTypes2, 346, "Primary associated
 SUPPRESSIBLE_LANGUAGE_FEATURE(UnavailableFromAsync, 0, "@_unavailableFromAsync", true)
 SUPPRESSIBLE_LANGUAGE_FEATURE(NoAsyncAvailability, 340, "@available(*, noasync)", true)
 
+EXPERIMENTAL_FEATURE(StaticAssert)
+EXPERIMENTAL_FEATURE(VariadicGenerics)
+EXPERIMENTAL_FEATURE(NamedOpaqueTypes)
+EXPERIMENTAL_FEATURE(FlowSensitiveConcurrencyCaptures)
+EXPERIMENTAL_FEATURE(MoveOnly)
+EXPERIMENTAL_FEATURE(OneWayClosureParameters)
+EXPERIMENTAL_FEATURE(TypeWitnessSystemInference)
+
+#undef EXPERIMENTAL_FEATURE
 #undef SUPPRESSIBLE_LANGUAGE_FEATURE
 #undef LANGUAGE_FEATURE

include/swift/Basic/LangOptions.h

@@ -18,13 +18,15 @@
 #ifndef SWIFT_BASIC_LANGOPTIONS_H
 #define SWIFT_BASIC_LANGOPTIONS_H
 
+#include "swift/Basic/Feature.h"
 #include "swift/Basic/FunctionBodySkipping.h"
 #include "swift/Basic/LLVM.h"
 #include "swift/Basic/Version.h"
 #include "swift/Config.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Triple.h"
@@ -312,23 +314,13 @@ namespace swift {
     /// Specifies how strict concurrency checking will be.
     StrictConcurrency StrictConcurrencyLevel = StrictConcurrency::Targeted;
 
-    /// Enable experimental #assert feature.
-    bool EnableExperimentalStaticAssert = false;
-
     /// Enable experimental concurrency model.
     bool EnableExperimentalConcurrency = false;
 
-    /// Enable experimental support for named opaque result types, e.g.
-    /// `func f() -> <T> T`.
-    bool EnableExperimentalNamedOpaqueTypes = false;
-
     /// Enable support for implicitly opening existential argument types
     /// in calls to generic functions.
     bool EnableOpenedExistentialTypes = false;
 
-    /// Enable experimental flow-sensitive concurrent captures.
-    bool EnableExperimentalFlowSensitiveConcurrentCaptures = false;
-
     /// Disable experimental ClangImporter diagnostics.
     bool DisableExperimentalClangImporterDiagnostics = false;
 
@@ -338,16 +330,6 @@ namespace swift {
     /// Enable inference of Sendable conformances for public types.
     bool EnableInferPublicSendable = false;
 
-    /// Enable experimental 'move only' features.
-    bool EnableExperimentalMoveOnly = false;
-
-    /// Enable variadic generics.
-    bool EnableExperimentalVariadicGenerics = false;
-
-    /// Enable experimental associated type inference using type witness
-    /// systems.
-    bool EnableExperimentalAssociatedTypeInference = false;
-
     /// Disable the implicit import of the _Concurrency module.
     bool DisableImplicitConcurrencyModuleImport =
         !SWIFT_IMPLICIT_CONCURRENCY_IMPORT;
@@ -369,6 +351,9 @@ namespace swift {
     /// behavior. This is a staging flag, and will be removed in the future.
     bool EnableNewOperatorLookup = false;
 
+    /// The set of features that have been enabled.
+    llvm::SmallSet<Feature, 2> Features;
+
     /// Use Clang function types for computing canonical types.
     /// If this option is false, the clang function types will still be computed
     /// but will not be used for checking type equality.
@@ -616,6 +601,13 @@ namespace swift {
       return EffectiveLanguageVersion.isVersionAtLeast(major, minor);
     }
 
+    /// Determine whether the given feature is enabled.
+    bool hasFeature(Feature feature) const;
+
+    /// Determine whether the given feature is enabled, looking up the feature
+    /// by name.
+    bool hasFeature(llvm::StringRef featureName) const;
+
     /// Returns true if the given platform condition argument represents
     /// a supported target operating system.
     ///
@@ -725,10 +717,6 @@ namespace swift {
     /// Disable constraint system performance hacks.
     bool DisableConstraintSolverPerformanceHacks = false;
 
-    /// Enable experimental support for one-way constraints for the
-    /// parameters of closures.
-    bool EnableOneWayClosureParameters = false;
-
     /// See \ref FrontendOptions.PrintFullConvention
     bool PrintFullConvention = false;
   };

include/swift/Option/Options.td

@@ -691,6 +691,11 @@ def strict_concurrency : Joined<["-"], "strict-concurrency=">,
            "concurrency model, or 'complete' ('Sendable' and other checking is "
            "enabled for all code in the module)">;
 
+def enable_experimental_feature :
+  Separate<["-"], "enable-experimental-feature">,
+  Flags<[FrontendOption]>,
+  HelpText<"Enable an experimental feature">;
+
 def Rpass_EQ : Joined<["-"], "Rpass=">,
   Flags<[FrontendOption]>,
   HelpText<"Report performed transformations by optimization passes whose "

lib/AST/ASTPrinter.cpp

@@ -2999,6 +2999,30 @@ static bool usesFeatureNoAsyncAvailability(Decl *decl) {
    return decl->getAttrs().getNoAsync(decl->getASTContext()) != nullptr;
 }
 
+static bool usesFeatureVariadicGenerics(Decl *decl) {
+  return false;
+}
+
+static bool usesFeatureNamedOpaqueTypes(Decl *decl) {
+  return false;
+}
+
+static bool usesFeatureFlowSensitiveConcurrencyCaptures(Decl *decl) {
+  return false;
+}
+
+static bool usesFeatureMoveOnly(Decl *decl) {
+  return false;
+}
+
+static bool usesFeatureOneWayClosureParameters(Decl *decl) {
+  return false;
+}
+
+static bool usesFeatureTypeWitnessSystemInference(Decl *decl) {
+  return false;
+}
+
 static void
 suppressingFeatureNoAsyncAvailability(PrintOptions &options,
                                       llvm::function_ref<void()> action) {

lib/Basic/LangOptions.cpp

@@ -224,6 +224,20 @@ bool LangOptions::isCustomConditionalCompilationFlagSet(StringRef Name) const {
       != CustomConditionalCompilationFlags.end();
 }
 
+bool LangOptions::hasFeature(Feature feature) const {
+  if (Features.contains(feature))
+    return true;
+
+  return false;
+}
+
+bool LangOptions::hasFeature(llvm::StringRef featureName) const {
+  if (auto feature = getExperimentalFeature(featureName))
+    return hasFeature(*feature);
+
+  return false;
+}
+
 std::pair<bool, bool> LangOptions::setTarget(llvm::Triple triple) {
   clearAllPlatformConditionValues();
 
@@ -409,6 +423,15 @@ bool swift::isSuppressibleFeature(Feature feature) {
   llvm_unreachable("covered switch");
 }
 
+llvm::Optional<Feature> swift::getExperimentalFeature(llvm::StringRef name) {
+  return llvm::StringSwitch<Optional<Feature>>(name)
+#define LANGUAGE_FEATURE(FeatureName, SENumber, Description, Option)
+#define EXPERIMENTAL_FEATURE(FeatureName) \
+                   .Case(#FeatureName, Feature::FeatureName)
+#include "swift/Basic/Features.def"
+                   .Default(None);
+}
+
 DiagnosticBehavior LangOptions::getAccessNoteFailureLimit() const {
   switch (AccessNoteBehavior) {
   case AccessNoteDiagnosticBehavior::Ignore:

lib/Driver/ToolChains.cpp

@@ -236,6 +236,7 @@ void ToolChain::addCommonFrontendArgs(const OutputInfo &OI,
                        options::OPT_disable_actor_data_race_checks);
   inputArgs.AddLastArg(arguments, options::OPT_warn_concurrency);
   inputArgs.AddLastArg(arguments, options::OPT_strict_concurrency);
+  inputArgs.AddAllArgs(arguments, options::OPT_enable_experimental_feature);
   inputArgs.AddLastArg(arguments, options::OPT_warn_implicit_overrides);
   inputArgs.AddLastArg(arguments, options::OPT_typo_correction_limit);
   inputArgs.AddLastArg(arguments, options::OPT_enable_app_extension);

lib/Frontend/CompilerInvocation.cpp

@@ -447,35 +447,18 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.DiagnosticsEditorMode |= Args.hasArg(OPT_diagnostics_editor_mode,
                                             OPT_serialize_diagnostics_path);
 
-  Opts.EnableExperimentalStaticAssert |=
-    Args.hasArg(OPT_enable_experimental_static_assert);
-
   Opts.EnableExperimentalConcurrency |=
     Args.hasArg(OPT_enable_experimental_concurrency);
 
-  Opts.EnableExperimentalNamedOpaqueTypes |=
-      Args.hasArg(OPT_enable_experimental_named_opaque_types);
-
   Opts.EnableOpenedExistentialTypes =
     Args.hasFlag(OPT_enable_experimental_opened_existential_types,
                  OPT_disable_experimental_opened_existential_types,
                  true);
 
-  Opts.EnableExperimentalVariadicGenerics |=
-    Args.hasArg(OPT_enable_experimental_variadic_generics);
-
-  Opts.EnableExperimentalAssociatedTypeInference |=
-      Args.hasArg(OPT_enable_experimental_associated_type_inference);
-
-  Opts.EnableExperimentalMoveOnly |=
-    Args.hasArg(OPT_enable_experimental_move_only);
-
   Opts.EnableInferPublicSendable |=
     Args.hasFlag(OPT_enable_infer_public_concurrent_value,
                  OPT_disable_infer_public_concurrent_value,
                  false);
-  Opts.EnableExperimentalFlowSensitiveConcurrentCaptures |=
-    Args.hasArg(OPT_enable_experimental_flow_sensitive_concurrent_captures);
 
   Opts.DisableExperimentalClangImporterDiagnostics |=
       Args.hasArg(OPT_disable_experimental_clang_importer_diagnostics);
@@ -649,6 +632,37 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     Opts.addCustomConditionalCompilationFlag(A->getValue());
   }
 
+  for (const Arg *A : Args.filtered(OPT_enable_experimental_feature)) {
+    // If this is a known experimental feature, allow it in +Asserts
+    // (non-release) builds for testing purposes.
+    if (auto feature = getExperimentalFeature(A->getValue())) {
+#ifdef NDEBUG
+      Diags.diagnose(SourceLoc(),
+                     diag::error_experimental_feature_not_available,
+                     A->getValue());
+#endif
+
+      Opts.Features.insert(*feature);
+    }
+  }
+
+  // Map historical flags over to experimental features. We do this for all
+  // compilers because that's how existing experimental feature flags work.
+  if (Args.hasArg(OPT_enable_experimental_variadic_generics))
+    Opts.Features.insert(Feature::VariadicGenerics);
+  if (Args.hasArg(OPT_enable_experimental_static_assert))
+    Opts.Features.insert(Feature::StaticAssert);
+  if (Args.hasArg(OPT_enable_experimental_named_opaque_types))
+    Opts.Features.insert(Feature::NamedOpaqueTypes);
+  if (Args.hasArg(OPT_enable_experimental_flow_sensitive_concurrent_captures))
+    Opts.Features.insert(Feature::FlowSensitiveConcurrencyCaptures);
+  if (Args.hasArg(OPT_enable_experimental_move_only))
+    Opts.Features.insert(Feature::MoveOnly);
+  if (Args.hasArg(OPT_experimental_one_way_closure_params))
+    Opts.Features.insert(Feature::OneWayClosureParameters);
+  if (Args.hasArg(OPT_enable_experimental_associated_type_inference))
+    Opts.Features.insert(Feature::TypeWitnessSystemInference);
+
   Opts.EnableAppExtensionRestrictions |= Args.hasArg(OPT_enable_app_extension);
 
   Opts.EnableSwift3ObjCInference =
@@ -1098,9 +1112,6 @@ static bool ParseTypeCheckerArgs(TypeCheckerOptions &Opts, ArgList &Args,
   // Always enable operator designated types for the standard library.
   Opts.EnableOperatorDesignatedTypes |= FrontendOpts.ParseStdlib;
 
-  Opts.EnableOneWayClosureParameters |=
-      Args.hasArg(OPT_experimental_one_way_closure_params);
-
   Opts.PrintFullConvention |=
       Args.hasArg(OPT_experimental_print_full_convention);
 

lib/Parse/ParseDecl.cpp

@@ -2908,7 +2908,7 @@ bool Parser::parseNewDeclAttribute(DeclAttributes &Attributes, SourceLoc AtLoc,
     break;
   }
   case DAK_TypeSequence: {
-    if (Context.LangOpts.EnableExperimentalVariadicGenerics) {
+    if (Context.LangOpts.hasFeature(Feature::VariadicGenerics)) {
       auto range = SourceRange(Loc, Tok.getRange().getStart());
       Attributes.add(TypeSequenceAttr::create(Context, AtLoc, range));
     } else {

lib/Parse/ParseStmt.cpp

@@ -2719,7 +2719,7 @@ ParserResult<Stmt> Parser::parseStmtPoundAssert() {
 
   // We check this after consuming everything, so that the SyntaxContext
   // understands this statement even when the feature is disabled.
-  if (!Context.LangOpts.EnableExperimentalStaticAssert) {
+  if (!Context.LangOpts.hasFeature(Feature::StaticAssert)) {
     diagnose(startLoc, diag::pound_assert_disabled);
     return makeParserError();
   }

lib/Parse/ParseType.cpp

@@ -564,7 +564,7 @@ ParserResult<TypeRepr> Parser::parseType(
 
 ParserResult<TypeRepr> Parser::parseTypeWithOpaqueParams(Diag<> MessageID) {
   GenericParamList *genericParams = nullptr;
-  if (Context.LangOpts.EnableExperimentalNamedOpaqueTypes) {
+  if (Context.LangOpts.hasFeature(Feature::NamedOpaqueTypes)) {
     auto result = maybeParseGenericParams();
     genericParams = result.getPtrOrNull();
     if (result.hasCodeCompletion())

lib/SILGen/SILGenDecl.cpp

@@ -474,7 +474,7 @@ class LetValueInitialization : public Initialization {
 
     // Make sure that we have a non-address only type when binding a
     // @_noImplicitCopy let.
-    if (SGF.getASTContext().LangOpts.EnableExperimentalMoveOnly &&
+    if (SGF.getASTContext().LangOpts.hasFeature(Feature::MoveOnly) &&
         lowering.isAddressOnly() &&
         vd->getAttrs().hasAttribute<NoImplicitCopyAttr>()) {
       auto d = diag::noimplicitcopy_used_on_generic_or_existential;
@@ -556,7 +556,7 @@ class LetValueInitialization : public Initialization {
 
     if (SGF.getASTContext().SILOpts.supportsLexicalLifetimes(SGF.getModule()) &&
         value->getOwnershipKind() != OwnershipKind::None) {
-      if (!SGF.getASTContext().LangOpts.EnableExperimentalMoveOnly) {
+      if (!SGF.getASTContext().LangOpts.hasFeature(Feature::MoveOnly)) {
         value = SILValue(
             SGF.B.createBeginBorrow(PrologueLoc, value, /*isLexical*/ true));
       } else {
@@ -1801,7 +1801,7 @@ void SILGenFunction::destroyLocalVariable(SILLocation silLoc, VarDecl *vd) {
     return;
   }
 
-  if (getASTContext().LangOpts.EnableExperimentalMoveOnly) {
+  if (getASTContext().LangOpts.hasFeature(Feature::MoveOnly)) {
     if (auto *mvi = dyn_cast<MarkMustCheckInst>(Val.getDefiningInstruction())) {
       if (mvi->isNoImplicitCopy()) {
         if (auto *cvi = dyn_cast<CopyValueInst>(mvi->getOperand())) {