From 8efa23bb996161af74f89401902450e51e9d4b54 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Fri, 10 Jul 2020 15:56:24 +0200
Subject: [PATCH] Avoid a redundant hash

---
 src/libstore/store-api.cc | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 46587a49a..8d46bb436 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -229,14 +229,17 @@ ValidPathInfo Store::addToStoreSlow(std::string_view name, const Path & srcPath,
     /* FIXME: inefficient: we're reading/hashing 'tmpFile' three
        times. */
 
+    auto [narHash, narSize] = hashPath(htSHA256, srcPath);
+
     auto hash = method == FileIngestionMethod::Recursive
-        ? hashPath(hashAlgo, srcPath).first
+        ? hashAlgo == htSHA256
+          ? narHash
+          : hashPath(hashAlgo, srcPath).first
         : hashFile(hashAlgo, srcPath);
 
     if (expectedCAHash && expectedCAHash != hash)
         throw Error("hash mismatch for '%s'", srcPath);
 
-    auto [narHash, narSize] = hashPath(htSHA256, srcPath);
     ValidPathInfo info(makeFixedOutputPath(method, hash, name));
     info.narHash = narHash;
     info.narSize = narSize;