nix doctor: add warning if client/daemon protocol mismatches

A protocol mismatch can sometimes cause problems when using specific
features with an older daemon. For example:

Nix 2.0 changed the way files are compied to the store.  The daemon is
backwards compatible and can still handle older clients, however a 1.11
nix-daemon isn't forwards compatible.

1 files changed, 26 insertions, 1 deletions

diff --git a/src/nix/doctor.cc b/src/nix/doctor.cc
index fb4fc2a6e7e2..6ef5eb9d30e4 100644
--- a/src/nix/doctor.cc
+++ b/src/nix/doctor.cc
@@ -1,9 +1,20 @@
 #include "command.hh"
 #include "shared.hh"
 #include "store-api.hh"
+#include "worker-protocol.hh"
 
 using namespace nix;
 
+std::string formatProtocol(unsigned int proto)
+{
+    if (proto) {
+        auto major = GET_PROTOCOL_MAJOR(proto) >> 8;
+        auto minor = GET_PROTOCOL_MINOR(proto);
+        return (format("%1%.%2%") % major % minor).str();
+    }
+    return "unknown";
+}
+
 struct CmdDoctor : StoreCommand
 {
     std::string name() override
@@ -19,8 +30,22 @@ struct CmdDoctor : StoreCommand
     void run(ref<Store> store) override
     {
         std::cout << "Store uri: " << store->getUri() << std::endl;
+        std::cout << std::endl;
+
+        checkStoreProtocol(store->getProtocol());
+    }
+
+    void checkStoreProtocol(unsigned int proto) {
+        if (PROTOCOL_VERSION != proto) {
+            std::cout << "Warning: protocol version of this client does not match the store." << std::endl;
+            std::cout << "While this is not necessarily a problem it's recommended to keep the client in" << std::endl;
+            std::cout << "sync with the daemon." << std::endl;
+            std::cout << std::endl;
+            std::cout << "Client protocol: " << formatProtocol(PROTOCOL_VERSION) << std::endl;
+            std::cout << "Store protocol: " << formatProtocol(proto) << std::endl;
+            std::cout << std::endl;
+        }
     }
 };
 
 static RegisterCommand r1(make_ref<CmdDoctor>());
-