* fetchsvn' now requires the MD5 hash (as computed by nix-hash') of

the tree being fetched from a Subversion repository.  The revision
  number is now optional (and defaults to HEAD).

  This makes `fetchsvn' more pure.  First, a URL/revision tuple does
  not uniquely identify a file resource, since the repository itself
  might change.  Second, `svn:external' attributes can cause arbitrary
  resources to be exported.

  A script `nix-prefetch-svn' has been provided to determine the hash
  of a URL.

svn path=/nixpkgs/trunk/; revision=938

pkgs/build-support/fetchsvn/builder.sh

@@ -1,8 +1,19 @@
-buildinputs="$subversion"
 . $stdenv/setup
 
-echo "exporting $url (r$rev) into $out..."
+header "exporting $url (r$rev) into $out"
 
-svn export -r $rev "$url" $out || exit 1
+prefetch=$(dirname $out)/svn-checkout-tmp-$md5
+echo $prefetch
+if test -e "$prefetch"; then
+    mv $prefetch $out
+else
+    svn export -r "$rev" "$url" $out
+fi
 
-echo $rev > $out/svn-revision || exit 1
+actual=$(nix-hash $out)
+if test "$actual" != "$md5"; then
+    echo "hash is $actual, expected $md5" >&2
+    exit 1
+fi
+
+stopNest