libexpr: Introduce Deprecated features

They are like experimental features, but opt-in instead of opt-out. They
will allow us to gracefully remove language features. See #437

Change-Id: I9ca04cc48e6926750c4d622c2b229b25cc142c42

1 files changed, 6 insertions, 0 deletions

diff --git a/src/nix/main.cc b/src/nix/main.cc
index 9cbe303ac..5356a0d04 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -14,6 +14,7 @@
 #include "loggers.hh"
 #include "markdown.hh"
 #include "experimental-features-json.hh"
+#include "deprecated-features-json.hh"
 
 #include <sys/types.h>
 #include <sys/socket.h>
@@ -422,6 +423,11 @@ void mainWrapped(int argc, char * * argv)
         return;
     }
 
+    if (argc == 2 && std::string(argv[1]) == "__dump-dp-features") {
+        logger->cout(documentDeprecatedFeatures().dump());
+        return;
+    }
+
     Finally printCompletions([&]()
     {
         if (args.completions) {