Don't embed compile-time timestamps into generated files.

Currently the build is not reproducible because make(1) runs
date(1) to provide the month and the year for the man page. Fix
this by honouring SOURCE_DATE_EPOCH as described in

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

Signed-off-by: Andre Noll <maan@tuebingen.mpg.de>

diff --git a/Makefile b/Makefile
index 408e3a5ac123dff22cd744a1487e18de3ed53c64..3c7bde206f1e977188ab753a6b86f53331cde74c 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -21,7 +21,15 @@ INSTALL := install
 GZIP := gzip -f9
 ZCAT := zcat
 
-DATE := $(shell date '+%B %Y')
+DATE_FMT := +%B %Y
+# To get a reproducible build, we use $(SOURCE_DATE_EPOCH) instead of the
+# current time if this variable is set.
+ifdef SOURCE_DATE_EPOCH
+       DATE := $(shell LC_ALL=C date -u -d '@$(SOURCE_DATE_EPOCH)' \
+               '$(DATE_FMT)' 2>/dev/null || LC_ALL=C date -u '$(DATE_FMT)')
+else
+       DATE := $(shell date '+$(DATE_FMT)')
+endif
 GIT_VERSION := $(shell ./version-gen.sh)
 PLAIN_VERSION := $(firstword $(subst -, , $(GIT_VERSION)))
 MAJOR_VERSION := $(firstword $(subst ., , $(PLAIN_VERSION)))