fetchdarcs: add mirror support

pkgs/build-support/fetchdarcs/builder.sh

@@ -14,8 +14,19 @@ elif test -n "$context"; then
     tagflags="--context=$context"
 fi
 
-echo "Cloning $url ${tagtext} into $out"
+# Repository list may contain ?. No glob expansion for that.
+set -o noglob
 
-darcs clone --lazy $tagflags "$url" "$out"
-# remove metadata, because it can change
-rm -rf "$out/_darcs"
+for repository in $repositories; do
+    echo "Trying to clone $repository $tagtext into $out …"
+    if darcs clone --lazy $tagflags "$repository" "$out"; then
+        # remove metadata, because it can change
+        rm -rf "$out/_darcs"
+        exit 0
+    fi
+done
+
+set +o noglob
+
+echo "Error: couldn’t clone repository from any mirror" 1>&2
+exit 1

pkgs/build-support/fetchdarcs/default.nix

@@ -8,7 +8,11 @@
 lib.makeOverridable (
   lib.fetchers.withNormalizedHash { } (
     {
+      # Repository to fetch
       url,
+      # Additional list of repositories specifying alternative download
+      # location to be tried in order, if the prior repository failed to fetch.
+      mirrors ? [ ],
       rev ? null,
       context ? null,
       outputHash ? lib.fakeHash,
@@ -27,11 +31,12 @@ lib.makeOverridable (
       outputHashMode = "recursive";
 
       inherit
-        url
         rev
         context
         name
         ;
+
+      repositories = [ url ] ++ mirrors;
     }
   )
 )