[pacman-dev] [PATCH v3] makepkg: respect $SOURCE_DATE_EPOCH to activate reproducible builds

[Eli Schwartz]

If SOURCE_DATE_EPOCH is set, `touch` all source files before running
build() to fix the modification times. This works around build systems
and compilers that embed the file modification times into the file
contents of release artifacts.

Signed-off-by: Eli Schwartz <eschwartz at archlinux.org>
---

v3: add makepkg(8) documentation

 doc/makepkg.8.txt     | 16 ++++++++++++++++
 scripts/makepkg.sh.in | 14 +++++++++++++-
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/doc/makepkg.8.txt b/doc/makepkg.8.txt
index 2dff1b19..4258e6bd 100644
--- a/doc/makepkg.8.txt
+++ b/doc/makepkg.8.txt
@@ -206,6 +206,7 @@ Options
 *\--printsrcinfo*::
 	Generate and print the SRCINFO file to stdout.
 
+
 Additional Features
 -------------------
 makepkg supports building development versions of packages without having to
@@ -214,6 +215,19 @@ separate utility 'versionpkg'. See linkman:PKGBUILD[5] for details on how to
 set up a development PKGBUILD.
 
 
+Reproducibility
+---------------
+makepkg is designed to be compatible with
+link:https://reproducible-builds.org/docs/[Reproducible Builds]. If the
+**SOURCE_DATE_EPOCH** environment variable is set, it will be exported to
+subprocesses, and source and package file modification times and package
+metadata will be unified based on the timestamp specified.
+
+If the **SOURCE_DATE_EPOCH** environment variable is not set, makepkg will use
+its own start date for internal use, but is not responsible for ensuring the
+package files themselves are built reproducibly.
+
+
 Environment Variables
 ---------------------
 **PACMAN**::
@@ -265,6 +279,8 @@ Environment Variables
 	Specify a key to use when signing packages, overriding the GPGKEY setting
 	in linkman:makepkg.conf[5]
 
+**SOURCE_DATE_EPOCH=**"<date>"::
+	Used for link:https://reproducible-builds.org/docs/[Reproducible Builds].
 
 Configuration
 -------------
diff --git a/scripts/makepkg.sh.in b/scripts/makepkg.sh.in
index 20e9dd7e..77d39ca5 100644
--- a/scripts/makepkg.sh.in
+++ b/scripts/makepkg.sh.in
@@ -79,6 +79,7 @@ PKGFUNC=0
 PKGVERFUNC=0
 PREPAREFUNC=0
 REPKG=0
+REPRODUCIBLE=0
 RMDEPS=0
 SKIPCHECKSUMS=0
 SKIPPGPCHECK=0
@@ -87,7 +88,12 @@ SPLITPKG=0
 SOURCEONLY=0
 VERIFYSOURCE=0
 
-export SOURCE_DATE_EPOCH=${SOURCE_DATE_EPOCH:-$(date +%s)}
+if [[ -n $SOURCE_DATE_EPOCH ]]; then
+	REPRODUCIBLE=1
+else
+	SOURCE_DATE_EPOCH=$(date +%s)
+fi
+export SOURCE_DATE_EPOCH
 
 PACMAN_OPTS=()
 
@@ -475,6 +481,12 @@ run_prepare() {
 }
 
 run_build() {
+	if (( REPRODUCIBLE )); then
+		# We have activated reproducible builds, so unify source times before
+		# building
+		find "$srcdir" -exec touch -h -d @$SOURCE_DATE_EPOCH {} +
+	fi
+
 	run_function_safe "build"
 }
 
-- 
2.14.1