8 files changed, 141 insertions, 2 deletions
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index 88d2574e86ef..26e1851981db 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -303,6 +303,12 @@ struct LegacySSHStore : public Store
     {
         auto conn(connections->get());
     }
+
+    unsigned int getProtocol() override
+    {
+        auto conn(connections->get());
+        return conn->remoteVersion;
+    }
 };
 
 static RegisterStoreImplementation regStore([](
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 197b9d78995b..216f3417c4a8 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -1338,6 +1338,12 @@ void LocalStore::verifyPath(const Path & path, const PathSet & store,
 }
 
 
+unsigned int LocalStore::getProtocol()
+{
+    return PROTOCOL_VERSION;
+}
+
+
 #if defined(FS_IOC_SETFLAGS) && defined(FS_IOC_GETFLAGS) && defined(FS_IMMUTABLE_FL)
 
 static void makeMutable(const Path & path)
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index 746bdbeed793..fce963433a5e 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -209,6 +209,8 @@ public:
 
     void registerValidPaths(const ValidPathInfos & infos);
 
+    unsigned int getProtocol() override;
+
     void vacuumDB();
 
     /* Repair the contents of the given path by redownloading it using
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index ef8b0e53b808..def140cfbe18 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -693,6 +693,13 @@ void RemoteStore::connect()
 }
 
 
+unsigned int RemoteStore::getProtocol()
+{
+    auto conn(connections->get());
+    return conn->daemonVersion;
+}
+
+
 void RemoteStore::flushBadConnections()
 {
     connections->flushBad();
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index 7f9d7d1f56d6..4f554b5980e8 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -98,6 +98,8 @@ public:
 
     void connect() override;
 
+    unsigned int getProtocol() override;
+
     void flushBadConnections();
 
 protected:
@@ -127,7 +129,7 @@ protected:
 
     ConnectionHandle getConnection();
 
-    friend class ConnectionHandle;
+    friend struct ConnectionHandle;
 
 private:
 
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 099818ed6f69..106b2be5e6b2 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -599,6 +599,12 @@ public:
        a notion of connection. Otherwise this is a no-op. */
     virtual void connect() { };
 
+    /* Get the protocol version of this store or it's connection. */
+    virtual unsigned int getProtocol()
+    {
+        return 0;
+    };
+
     /* Get the priority of the store, used to order substituters. In
        particular, binary caches can specify a priority field in their
        "nix-cache-info" file. Lower value means higher priority. */
diff --git a/src/nix/doctor.cc b/src/nix/doctor.cc
new file mode 100644
index 000000000000..1ce3efcb0415
--- /dev/null
+++ b/src/nix/doctor.cc
@@ -0,0 +1,110 @@
+#include "command.hh"
+#include "serve-protocol.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
+    {
+        return "doctor";
+    }
+
+    std::string description() override
+    {
+        return "check your system for potential problems";
+    }
+
+    void run(ref<Store> store) override
+    {
+        std::cout << "Store uri: " << store->getUri() << std::endl;
+        std::cout << std::endl;
+
+        auto type = getStoreType();
+
+        if (type < tOther) {
+            checkNixInPath();
+            checkProfileRoots(store);
+        }
+        checkStoreProtocol(store->getProtocol());
+    }
+
+    void checkNixInPath()
+    {
+        PathSet dirs;
+
+        for (auto & dir : tokenizeString<Strings>(getEnv("PATH"), ":"))
+            if (pathExists(dir + "/nix-env"))
+                dirs.insert(dirOf(canonPath(dir + "/nix-env", true)));
+
+        if (dirs.size() != 1) {
+            std::cout << "Warning: multiple versions of nix found in PATH." << std::endl;
+            std::cout << std::endl;
+            for (auto & dir : dirs)
+                std::cout << "  " << dir << std::endl;
+            std::cout << std::endl;
+        }
+    }
+
+    void checkProfileRoots(ref<Store> store)
+    {
+        PathSet dirs;
+
+        for (auto & dir : tokenizeString<Strings>(getEnv("PATH"), ":")) {
+            Path profileDir = dirOf(dir);
+            try {
+                Path userEnv = canonPath(profileDir, true);
+
+                if (store->isStorePath(userEnv) && hasSuffix(userEnv, "user-environment")) {
+                    while (profileDir.find("/profiles/") == std::string::npos && isLink(profileDir))
+                        profileDir = absPath(readLink(profileDir), dirOf(profileDir));
+
+                    if (profileDir.find("/profiles/") == std::string::npos)
+                        dirs.insert(dir);
+                }
+            } catch (SysError &) {}
+        }
+
+        if (!dirs.empty()) {
+            std::cout << "Warning: found profiles outside of " << settings.nixStateDir << "/profiles." << std::endl;
+            std::cout << "The generation this profile points to might not have a gcroot and could be" << std::endl;
+            std::cout << "garbage collected, resulting in broken symlinks." << std::endl;
+            std::cout << std::endl;
+            for (auto & dir : dirs)
+                std::cout << "  " << dir << std::endl;
+            std::cout << std::endl;
+        }
+    }
+
+    void checkStoreProtocol(unsigned int storeProto)
+    {
+        unsigned int clientProto = GET_PROTOCOL_MAJOR(SERVE_PROTOCOL_VERSION) == GET_PROTOCOL_MAJOR(storeProto)
+            ? SERVE_PROTOCOL_VERSION
+            : PROTOCOL_VERSION;
+
+        if (clientProto != storeProto) {
+            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(clientProto) << std::endl;
+            std::cout << "Store protocol: " << formatProtocol(storeProto) << std::endl;
+            std::cout << std::endl;
+        }
+    }
+};
+
+static RegisterCommand r1(make_ref<CmdDoctor>());
diff --git a/src/nix/local.mk b/src/nix/local.mk
index 168936314dcd..bdcca33d2a6f 100644
--- a/src/nix/local.mk
+++ b/src/nix/local.mk
@@ -21,6 +21,6 @@ nix_LIBS = libexpr libmain libstore libutil libformat
 nix_LDFLAGS = -pthread $(SODIUM_LIBS)
 
 $(foreach name, \
-  nix-build nix-channel nix-collect-garbage nix-copy-closure nix-daemon nix-env nix-hash nix-instantiate nix-prefetch-rul nix-shell nix-shore, \
+  nix-build nix-channel nix-collect-garbage nix-copy-closure nix-daemon nix-env nix-hash nix-instantiate nix-prefetch-url nix-shell nix-store, \
   $(eval $(call install-symlink, nix, $(bindir)/$(name))))
 $(eval $(call install-symlink, $(bindir)/nix, $(libexecdir)/nix/build-remote))