[SE-0361] Remove the feature flag for bound generic extensions.

Author: hborla

include/swift/AST/DiagnosticsSema.def

@@ -1907,9 +1907,6 @@ ERROR(extension_access_with_conformances,none,
       "protocol conformances", (DeclAttribute))
 ERROR(extension_metatype,none,
       "cannot extend a metatype %0", (Type))
-ERROR(extension_specialization,none,
-      "constrained extension must be declared on the unspecialized generic "
-      "type %0 with constraints specified by a 'where' clause", (Identifier))
 ERROR(extension_placeholder,none,
       "cannot extend a type that contains placeholders", ())
 ERROR(extension_stored_property,none,

include/swift/Basic/Features.def

@@ -101,13 +101,6 @@ EXPERIMENTAL_FEATURE(MoveOnly)
 EXPERIMENTAL_FEATURE(OneWayClosureParameters)
 EXPERIMENTAL_FEATURE(TypeWitnessSystemInference)
 
-/// Enable extensions of (sugared) bound generic types
-///
-/// \code
-/// extension [Int] { /**/ }
-/// \endcode
-EXPERIMENTAL_FEATURE(BoundGenericExtensions)
-
 /// Whether to enable experimental differentiable programming features:
 /// `@differentiable` declaration attribute, etc.
 EXPERIMENTAL_FEATURE(DifferentiableProgramming)

include/swift/Option/FrontendOptions.td

@@ -317,10 +317,6 @@ def enable_resilience : Flag<["-"], "enable-resilience">,
 def enable_experimental_async_top_level :
   Flag<["-"], "enable-experimental-async-top-level">,
   HelpText<"Enable experimental concurrency in top-level code">;
-
-def enable_experimental_bound_generic_extensions :
-  Flag<["-"], "enable-experimental-bound-generic-extensions">,
-  HelpText<"Enable experimental support for extensions of bound generic types">;
 }
 
 // HIDDEN FLAGS

lib/AST/ASTPrinter.cpp

@@ -3035,10 +3035,6 @@ static bool usesFeatureTypeWitnessSystemInference(Decl *decl) {
   return false;
 }
 
-static bool usesFeatureBoundGenericExtensions(Decl *decl) {
-  return false;
-}
-
 static bool usesFeatureDifferentiableProgramming(Decl *decl) {
   return false;
 }

lib/Frontend/CompilerInvocation.cpp

@@ -656,8 +656,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     Opts.Features.insert(Feature::OneWayClosureParameters);
   if (Args.hasArg(OPT_enable_experimental_associated_type_inference))
     Opts.Features.insert(Feature::TypeWitnessSystemInference);
-  if (Args.hasArg(OPT_enable_experimental_bound_generic_extensions))
-    Opts.Features.insert(Feature::BoundGenericExtensions);
   if (Args.hasArg(OPT_enable_experimental_forward_mode_differentiation))
     Opts.Features.insert(Feature::ForwardModeDifferentiation);
   if (Args.hasArg(OPT_enable_experimental_additive_arithmetic_derivation))

lib/Sema/TypeCheckDecl.cpp

@@ -2846,17 +2846,5 @@ ExtendedTypeRequest::evaluate(Evaluator &eval, ExtensionDecl *ext) const {
     return error();
   }
 
-  // By default, the user cannot extend a bound generic type, unless it's
-  // referenced via a non-generic typealias type.
-  if (!ext->getASTContext().LangOpts.hasFeature(
-          Feature::BoundGenericExtensions) &&
-      extendedType->isSpecialized() &&
-      !isNonGenericTypeAliasType(extendedType)) {
-    diags.diagnose(ext->getLoc(), diag::extension_specialization,
-                   extendedType->getAnyNominal()->getName())
-         .highlight(extendedRepr->getSourceRange());
-    return error();
-  }
-
   return extendedType;
 }