Set a fallback default value for SOURCE_DATE_EPOCH

This is used by some build tools to provide reproducible builds. See

  https://reproducible-builds.org/specs/source-date-epoch/

for more info.

Later, we'll want to set this to a more intelligent value (such as the
most recent mtime of any source file).

1 files changed, 8 insertions, 0 deletions

diff --git a/pkgs/stdenv/generic/setup.sh b/pkgs/stdenv/generic/setup.sh
index 4693974a2b77..d8de9ab2390b 100644
--- a/pkgs/stdenv/generic/setup.sh
+++ b/pkgs/stdenv/generic/setup.sh
@@ -184,6 +184,14 @@ installBin() {
 # Initialisation.
 
 
+# Set a fallback default value for SOURCE_DATE_EPOCH, used by some
+# build tools to provide a deterministic substitute for the "current"
+# time. Note that 1 = 1970-01-01 00:00:01. We don't use 0 because it
+# confuses some applications.
+export SOURCE_DATE_EPOCH
+: ${SOURCE_DATE_EPOCH:=1}
+
+
 # Wildcard expansions that don't match should expand to an empty list.
 # This ensures that, for instance, "for i in *; do ...; done" does the
 # right thing.