* Allow a known hash to be specified.

svn path=/nixpkgs/trunk/; revision=1892

pkgs/build-support/fetchsvn/nix-prefetch-svn

@@ -2,6 +2,7 @@
 
 url=$1
 rev=$2
+hash=$3
 
 if test -z "$url"; then
     echo "syntax: nix-prefetch-svn URL [REVISION]" >&2
@@ -10,27 +11,32 @@ fi
 
 test -n "$rev" || rev="HEAD"
 
-# !!! hacky; we should have a way to query the location of the store.
-if storeDir=$(which nix-store); then
-    storeDir=$(dirname $(dirname "$storeDir"))/store
-else
-    storeDir=/nix/store
+# Determine the hash, unless it was given.
+if test -z "$hash"; then
+
+    # !!! hacky; we should have a way to query the location of the store.
+    if storeDir=$(which nix-store); then
+        storeDir=$(dirname $(dirname "$storeDir"))/store
+    else
+        storeDir=/nix/store
+    fi
+
+    # !!! race? should be relatively safe, `svn export' barfs if $tmpPath exists.
+    tmpPath1=$storeDir/svn-checkout-tmp-$$
+
+    # Perform the checkout.
+    svn export -r "$rev" "$url" $tmpPath1 >&2
+
+    # Compute the hash.
+    hash=$(nix-hash $tmpPath1)
+    echo "hash is $hash" >&2
+
+    # Rename it so that the fetchsvn builder can find it.
+    tmpPath2=$storeDir/svn-checkout-tmp-$hash
+    test -e $tmpPath2 || mv $tmpPath1 $tmpPath2 # !!! race
+
 fi
 
-# !!! race? should be relatively safe, `svn export' barfs if $tmpPath exists.
-tmpPath1=$storeDir/svn-checkout-tmp-$$
-
-# Perform the checkout.
-svn export -r "$rev" "$url" $tmpPath1 >&2
-
-# Compute the hash.
-hash=$(nix-hash $tmpPath1)
-echo "hash is $hash" >&2
-
-# Rename it so that the fetchsvn builder can find it.
-tmpPath2=$storeDir/svn-checkout-tmp-$hash
-test -e $tmpPath2 || mv $tmpPath1 $tmpPath2 # !!! race
-
 # Create a Nix expression that does a fetchsvn.
 nixExpr=$(dirname $(readlink -f $0))/../../system/i686-linux.nix
 storeExpr=$( \
@@ -42,7 +48,9 @@ finalPath=$(nix-store -qnB --force-realise $storeExpr)
 
 echo "path is $finalPath" >&2
 
-rm -rf $tmpPath2 || true
+if test -n "$tmpPath2"; then
+    rm -rf $tmpPath2 || true
+fi
 
 echo $hash