daemon: Delegate deduplication to 'guix substitute'.

This removes the main source of latency between subsequent downloads.

* nix/libstore/build.cc (SubstitutionGoal::tryToRun): Add a
"deduplicate" key to ENV.
(SubstitutionGoal::finished): Remove call to 'optimisePath'.
* guix/scripts/substitute.scm (process-substitution)[destination-in-store?]
[dump-file/deduplicate*]: New variables.
Pass #:dump-file to 'restore-file'.
* guix/scripts/substitute.scm (guix-substitute)[deduplicate?]: New
variable.
Pass #:deduplicate? to 'process-substitution'.
* guix/serialization.scm (dump-file): Export and augment 'dump-file'.

1 files changed, 8 insertions, 5 deletions

diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index ea809c6971c..20d83fea4a8 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -2984,7 +2984,12 @@ void SubstitutionGoal::tryToRun()
 
     if (!worker.substituter) {
         const Strings args = { "substitute", "--substitute" };
-        const std::map<string, string> env = { { "_NIX_OPTIONS", settings.pack() } };
+        const std::map<string, string> env = {
+            { "_NIX_OPTIONS",
+              settings.pack() + "deduplicate="
+              + (settings.autoOptimiseStore ? "yes" : "no")
+            }
+        };
         worker.substituter = std::make_shared<Agent>(settings.guixProgram, args, env);
     }
 
@@ -3085,10 +3090,8 @@ void SubstitutionGoal::finished()
 
     if (repair) replaceValidPath(storePath, destPath);
 
-    /* Note: 'guix substitute' takes care of resetting timestamps and
-       permissions on 'destPath', so no need to do it here.  */
-
-    worker.store.optimisePath(storePath); // FIXME: combine with hashPath()
+    /* Note: 'guix substitute' takes care of resetting timestamps and of
+       deduplicating 'destPath', so no need to do it here.  */
 
     ValidPathInfo info2;
     info2.path = storePath;