Stuctured command stability

Prior to this, there was an ad-hoc whitelist in `main.cc`. Now, every
command states its stability.

In a future PR, we will adjust the manual to take advantage of this new
information in the JSON.
(It will be easier to do that once we have some experimental feature
docs to link too; see #5930 and #7798.)

1 files changed, 8 insertions, 0 deletions

diff --git a/src/nix/doctor.cc b/src/nix/doctor.cc
index 7da4549a1..354b03cf6 100644
--- a/src/nix/doctor.cc
+++ b/src/nix/doctor.cc
@@ -39,6 +39,14 @@ struct CmdDoctor : StoreCommand
 {
     bool success = true;
 
+    /**
+     * This command is stable before the others
+     */
+    std::optional<ExperimentalFeature> experimentalFeature() override
+    {
+        return std::nullopt;
+    }
+
     std::string description() override
     {
         return "check your system for potential problems and print a PASS or FAIL for each check";