fetchpijul: add mirror support

Author: toastal

pkgs/build-support/fetchpijul/default.nix

@@ -7,7 +7,11 @@
 
 lib.makeOverridable (
   {
+    # Remote to fetch
     url,
+    # Additional list of remotes specifying alternative download location to be
+    # tried in order, if the prior remote failed to fetch.
+    mirrors ? [ ],
     hash ? "",
     change ? null,
     state ? null,
@@ -36,12 +40,25 @@ lib.makeOverridable (
       installPhase = ''
         runHook preInstall
 
-        pijul clone \
-          ''${change:+--change "$change"} \
-          ''${state:+--state "$state"} \
-          --channel "$channel" \
-          "$url" \
-          "$out"
+        success=
+        for remote in $remotes; do
+          if
+            pijul clone \
+              ''${change:+--change "$change"} \
+              ''${state:+--state "$state"} \
+              --channel "$channel" \
+              "$remote" \
+              "$out"
+          then
+            success=1
+            break
+          fi
+        done
+
+        if [ -z "$success" ]; then
+          echo "Error: couldn’t clone remote from any mirror" 1>&2
+          exit 1
+        fi
 
         runHook postInstall
       '';
@@ -59,12 +76,13 @@ lib.makeOverridable (
       outputHash = if hash != "" then hash else lib.fakeHash;
 
       inherit
-        url
         change
         state
         channel
         ;
 
+      remotes = [ url ] ++ mirrors;
+
       impureEnvVars = lib.fetchers.proxyImpureEnvVars;
     }
 )