Add operation ‘nix-store --repair-path’

This operation allows fixing corrupted or accidentally deleted store
paths by redownloading them using substituters, if available.

Since the corrupted path cannot be replaced atomically, there is a
very small time window (one system call) during which neither the old
(corrupted) nor the new (repaired) contents are available.  So
repairing should be used with some care on critical packages like
Glibc.

1 files changed, 3 insertions, 2 deletions

diff --git a/scripts/copy-from-other-stores.pl.in b/scripts/copy-from-other-stores.pl.in
index 3ee6f075b27e..9ed7e4cc22c0 100755
--- a/scripts/copy-from-other-stores.pl.in
+++ b/scripts/copy-from-other-stores.pl.in
@@ -83,12 +83,13 @@ if ($ARGV[0] eq "--query") {
 
 
 elsif ($ARGV[0] eq "--substitute") {
-    die unless scalar @ARGV == 2;
+    die unless scalar @ARGV == 3;
     my $storePath = $ARGV[1];
+    my $destPath = $ARGV[2];
     my ($store, $sourcePath) = findStorePath $storePath;
     die unless $store;
     print STDERR "\n*** Copying `$storePath' from `$sourcePath'\n\n";
-    system("$binDir/nix-store --dump $sourcePath | $binDir/nix-store --restore $storePath") == 0
+    system("$binDir/nix-store --dump $sourcePath | $binDir/nix-store --restore $destPath") == 0
         or die "cannot copy `$sourcePath' to `$storePath'";
     print "\n"; # no hash to verify
 }