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, 4 insertions, 3 deletions

diff --git a/scripts/download-using-manifests.pl.in b/scripts/download-using-manifests.pl.in
index 8f66a292e361..c73511f85090 100755
--- a/scripts/download-using-manifests.pl.in
+++ b/scripts/download-using-manifests.pl.in
@@ -238,8 +238,9 @@ elsif ($ARGV[0] ne "--substitute") {
 }
 
 
-die unless scalar @ARGV == 2;
+die unless scalar @ARGV == 3;
 my $targetPath = $ARGV[1];
+my $destPath = $ARGV[2];
 $fast = 0;
 
 
@@ -324,7 +325,7 @@ while (scalar @path > 0) {
             # This was the last patch.  Unpack the final NAR archive
             # into the target path.
             print STDERR "  unpacking patched archive...\n";
-            system("$Nix::Config::binDir/nix-store --restore $v < $tmpNar2") == 0
+            system("$Nix::Config::binDir/nix-store --restore $destPath < $tmpNar2") == 0
                 or die "cannot unpack $tmpNar2 to `$v'\n";
         }
 
@@ -351,7 +352,7 @@ while (scalar @path > 0) {
                 or die "cannot download and unpack `$narFile->{url}' to `$v'\n";
         } else {
             # Unpack the archive to the target path.
-            system("$curl '$narFile->{url}' | $decompressor | $Nix::Config::binDir/nix-store --restore '$v'") == 0
+            system("$curl '$narFile->{url}' | $decompressor | $Nix::Config::binDir/nix-store --restore '$destPath'") == 0
                 or die "cannot download and unpack `$narFile->{url}' to `$v'\n";
         }