nix: Support the --repair flag

src/libmain/common-args.hh

@@ -2,6 +2,7 @@
 ///@file
 
 #include "args.hh"
+#include "repair-flag.hh"
 
 namespace nix {
 
@@ -49,4 +50,21 @@ struct MixJSON : virtual Args
     }
 };
 
+struct MixRepair : virtual Args
+{
+    RepairFlag repair = NoRepair;
+
+    MixRepair()
+    {
+        addFlag({
+            .longName = "repair",
+            .description =
+                "During evaluation, rewrite missing or corrupted files in the Nix store. "
+                "During building, rebuild missing or corrupted store paths.",
+            .category = miscCategory,
+            .handler = {&repair, Repair},
+        });
+    }
+};
+
 }