From d5f1cc3e949ebb8c69b6c0d202302b12839b9bd5 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 6 Nov 2019 12:01:37 +0100
Subject: [PATCH] Use revcount/last-modified for computing the flake
 fingerprint

The store path is not enough. For example, when we build a dirty tree,
commit, and build the clean tree, a re-evaluation is necessary because
the flake may depend on the lastModified or revCount attributes.
---
 src/libexpr/flake/flake.cc | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index d96c3c413..80726a257 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -686,7 +686,11 @@ Fingerprint ResolvedFlake::getFingerprint() const
     // and we haven't changed it, then it's sufficient to use
     // flake.sourceInfo.storePath for the fingerprint.
     return hashString(htSHA256,
-        fmt("%s;%s", flake.sourceInfo.storePath, lockFile));
+        fmt("%s;%d;%d;%s",
+            flake.sourceInfo.storePath,
+            flake.sourceInfo.revCount.value_or(0),
+            flake.sourceInfo.lastModified.value_or(0),
+            lockFile));
 }
 
 }