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

Author: hborla

include/swift/Basic/LangOptions.h

@@ -482,13 +482,6 @@ namespace swift {
     // FrontendOptions.
     bool AllowModuleWithCompilerErrors = false;
 
-    /// Enable extensions of (sugared) bound generic types
-    ///
-    /// \code
-    /// extension [Int] { /**/ }
-    /// \endcode
-    bool EnableExperimentalBoundGenericExtensions = true;
-
     /// A helper enum to represent whether or not we customized the default
     /// ASTVerifier behavior via a frontend flag. By default, we do not
     /// customize.

include/swift/Option/FrontendOptions.td

@@ -313,10 +313,6 @@ 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/Frontend/CompilerInvocation.cpp

@@ -517,9 +517,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
       Opts.EnableBareSlashRegexLiterals = false;
   }
 
-  Opts.EnableExperimentalBoundGenericExtensions |=
-    Args.hasArg(OPT_enable_experimental_bound_generic_extensions);
-
   Opts.DisableAvailabilityChecking |=
       Args.hasArg(OPT_disable_availability_checking);
   Opts.CheckAPIAvailabilityOnly |=

lib/Sema/TypeCheckDecl.cpp

@@ -2846,16 +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.EnableExperimentalBoundGenericExtensions &&
-      extendedType->isSpecialized() &&
-      !isNonGenericTypeAliasType(extendedType)) {
-    diags.diagnose(ext->getLoc(), diag::extension_specialization,
-                   extendedType->getAnyNominal()->getName())
-         .highlight(extendedRepr->getSourceRange());
-    return error();
-  }
-
   return extendedType;
 }