Merge branch 'short-circuit-subst' of https://github.com/Kha/nix

src/libstore/local-store.cc

@@ -1076,6 +1076,10 @@ void LocalStore::querySubstitutablePathInfos(const StorePathCAMap & paths, Subst
     if (!settings.useSubstitutes) return;
     for (auto & sub : getDefaultSubstituters()) {
         for (auto & path : paths) {
+            if (infos.find(path.first) != infos.end())
+                // choose first succeeding substituter
+                continue;
+
             auto subPath(path.first);
 
             // recompute store path so that we can use a different store root

src/libstore/store-api.hh

@@ -430,9 +430,10 @@ public:
     virtual StorePathSet querySubstitutablePaths(const StorePathSet & paths) { return {}; };
 
     /* Query substitute info (i.e. references, derivers and download
-       sizes) of a map of paths to their optional ca values. If a path
-       does not have substitute info, it's omitted from the resulting
-       ‘infos’ map. */
+       sizes) of a map of paths to their optional ca values. The info
+       of the first succeeding substituter for each path will be
+       returned. If a path does not have substitute info, it's omitted
+       from the resulting ‘infos’ map. */
     virtual void querySubstitutablePathInfos(const StorePathCAMap & paths,
         SubstitutablePathInfos & infos) { return; };