Frontend: Introduce an alias for the NoncopyableGenerics experimental feature.

The `.swiftinterface` of the standard library must remain compatible with some
older compilers. Unfortunately, some of those older compilers do not allow the
experimental feature `NoncopyableGenerics` to be enabled in production. To
allow the stdlib to build with non-copyable generics enabled and still have the
older compilers consume its interface, we have to use a new experimental
feature identifier that they do not know about.

Partially resolves rdar://125138945

Author: tshortli

include/swift/Basic/Features.def

@@ -319,6 +319,9 @@ EXPERIMENTAL_FEATURE(Embedded, true)
 /// Enables noncopyable generics
 SUPPRESSIBLE_EXPERIMENTAL_FEATURE(NoncopyableGenerics, true)
 
+// Alias for NoncopyableGenerics
+EXPERIMENTAL_FEATURE(NoncopyableGenerics2, true)
+
 /// Allow destructuring stored `let` bindings in structs.
 EXPERIMENTAL_FEATURE(StructLetDestructuring, true)
 

lib/AST/FeatureSet.cpp

@@ -568,6 +568,8 @@ static bool usesFeatureNoncopyableGenerics(Decl *decl) {
   return !inverseReqs.empty();
 }
 
+UNINTERESTING_FEATURE(NoncopyableGenerics2)
+
 static bool usesFeatureStructLetDestructuring(Decl *decl) {
   auto sd = dyn_cast<StructDecl>(decl);
   if (!sd)

lib/Frontend/CompilerInvocation.cpp

@@ -883,6 +883,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
 #else
       Opts.enableFeature(*feature);
 #endif
+
+      if (*feature == Feature::NoncopyableGenerics2)
+        Opts.enableFeature(Feature::NoncopyableGenerics);
     }
 
     // Hack: In order to support using availability macros in SPM packages, we

stdlib/cmake/modules/SwiftSource.cmake

@@ -612,7 +612,7 @@ function(_compile_swift_files
     list(APPEND swift_flags "-experimental-hermetic-seal-at-link")
   endif()
 
-  list(APPEND swift_flags "-enable-experimental-feature" "NoncopyableGenerics")
+  list(APPEND swift_flags "-enable-experimental-feature" "NoncopyableGenerics2")
 
   if(SWIFT_ENABLE_EXPERIMENTAL_NONESCAPABLE_TYPES)
     list(APPEND swift_flags "-enable-experimental-feature" "NonescapableTypes")