nix: Support the --repair flag

src/libcmd/command.cc

@@ -121,6 +121,8 @@ ref<EvalState> EvalCommand::getEvalState()
             #endif
             ;
 
+        evalState->repair = repair;
+
         if (startReplOnEvalErrors) {
             evalState->debugRepl = &AbstractNixRepl::runSimple;
         };

src/libcmd/common-eval-args.hh

@@ -2,6 +2,7 @@
 ///@file
 
 #include "args.hh"
+#include "common-args.hh"
 
 namespace nix {
 
@@ -10,7 +11,7 @@ class EvalState;
 class Bindings;
 struct SourcePath;
 
-struct MixEvalArgs : virtual Args
+struct MixEvalArgs : virtual Args, virtual MixRepair
 {
     static constexpr auto category = "Common evaluation options";