From 9c4e05766bb7f3776cfc5eb1a3da358419a65406 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 29 Apr 2020 15:50:59 +0200
Subject: [PATCH] nix copy: Move --from / --to check

This means you now get an error message *before* stuff gets built:

  $ nix copy .#hydraJobs.vendoredCrates
  error: you must pass '--from' and/or '--to'
  Try 'nix --help' for more information.
---
 src/nix/copy.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/nix/copy.cc b/src/nix/copy.cc
index 85c777d38..66993ac21 100644
--- a/src/nix/copy.cc
+++ b/src/nix/copy.cc
@@ -80,11 +80,16 @@ struct CmdCopy : StorePathsCommand
         return srcUri.empty() ? StoreCommand::createStore() : openStore(srcUri);
     }
 
-    void run(ref<Store> srcStore, StorePaths storePaths) override
+    void run(ref<Store> store) override
     {
         if (srcUri.empty() && dstUri.empty())
             throw UsageError("you must pass '--from' and/or '--to'");
 
+        StorePathsCommand::run(store);
+    }
+
+    void run(ref<Store> srcStore, StorePaths storePaths) override
+    {
         ref<Store> dstStore = dstUri.empty() ? openStore() : openStore(dstUri);
 
         copyPaths(srcStore, dstStore, storePathsToSet(storePaths),