Add experimental feature for AdditiveArithmetic derived conformances

Author: DougGregor

include/swift/Basic/Features.def

@@ -115,6 +115,9 @@ EXPERIMENTAL_FEATURE(DifferentiableProgramming)
 /// Whether to enable forward mode differentiation.
 EXPERIMENTAL_FEATURE(ForwardModeDifferentiation)
 
+/// Whether to enable experimental `AdditiveArithmetic` derived
+/// conformances.
+EXPERIMENTAL_FEATURE(AdditiveArithmeticDerivedConformances)
 
 #undef EXPERIMENTAL_FEATURE
 #undef FUTURE_FEATURE

include/swift/Basic/LangOptions.h

@@ -426,10 +426,6 @@ namespace swift {
     /// file.
     bool EmitFineGrainedDependencySourcefileDotFiles = false;
 
-    /// Whether to enable experimental `AdditiveArithmetic` derived
-    /// conformances.
-    bool EnableExperimentalAdditiveArithmeticDerivedConformances = false;
-
     /// Enable verification when every SubstitutionMap is constructed.
     bool VerifyAllSubstitutionMaps = false;
 

lib/AST/ASTPrinter.cpp

@@ -3047,6 +3047,10 @@ static bool usesFeatureForwardModeDifferentiation(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureAdditiveArithmeticDerivedConformances(Decl *decl) {
+  return false;
+}
+
 static void
 suppressingFeatureNoAsyncAvailability(PrintOptions &options,
                                       llvm::function_ref<void()> action) {

lib/Frontend/CompilerInvocation.cpp

@@ -544,9 +544,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   if (Args.hasArg(OPT_emit_fine_grained_dependency_sourcefile_dot_files))
     Opts.EmitFineGrainedDependencySourcefileDotFiles = true;
 
-  if (Args.hasArg(OPT_enable_experimental_additive_arithmetic_derivation))
-    Opts.EnableExperimentalAdditiveArithmeticDerivedConformances = true;
-
   Opts.DebuggerSupport |= Args.hasArg(OPT_debugger_support);
   if (Opts.DebuggerSupport)
     Opts.EnableDollarIdentifiers = true;
@@ -664,6 +661,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     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))
+    Opts.Features.insert(Feature::AdditiveArithmeticDerivedConformances);
 
   Opts.EnableAppExtensionRestrictions |= Args.hasArg(OPT_enable_app_extension);
 

lib/Sema/TypeChecker.cpp

@@ -379,7 +379,7 @@ bool swift::isAdditiveArithmeticConformanceDerivationEnabled(SourceFile &SF) {
   auto &ctx = SF.getASTContext();
   // Return true if `AdditiveArithmetic` derived conformances are explicitly
   // enabled.
-  if (ctx.LangOpts.EnableExperimentalAdditiveArithmeticDerivedConformances)
+  if (ctx.LangOpts.hasFeature(Feature::AdditiveArithmeticDerivedConformances))
     return true;
   // Otherwise, return true iff differentiable programming is enabled.
   // Differentiable programming depends on `AdditiveArithmetic` derived