[swift-ide-test] Add support for -enable-upcoming-feature

Author: NuriAmari

tools/swift-ide-test/swift-ide-test.cpp

@@ -865,6 +865,11 @@ static llvm::cl::list<std::string>
                              llvm::cl::desc("Enable an experimental feature"),
                              llvm::cl::cat(Category));
 
+static llvm::cl::list<std::string>
+  EnableUpcomingFeatures("enable-upcoming-feature",
+      llvm::cl::desc("Enable a feature that will be introduced in an upcoming language version"),
+      llvm::cl::cat(Category));
+
 static llvm::cl::list<std::string>
 AccessNotesPath("access-notes-path", llvm::cl::desc("Path to access notes file"),
                 llvm::cl::cat(Category));
@@ -4421,6 +4426,12 @@ int main(int argc, char *argv[]) {
     }
   }
 
+  for (const auto &featureArg : options::EnableUpcomingFeatures) {
+    if (auto feature = getUpcomingFeature(featureArg)) {
+      InitInvok.getLangOptions().Features.insert(*feature);
+    }
+  }
+
   if (!options::Triple.empty())
     InitInvok.setTargetTriple(options::Triple);
   if (!options::SwiftVersion.empty()) {