[PATCH v2 2/5] Makefile: under "make dist", include the sha1collisiondetection submodule

Include the sha1collisiondetection submodule when running "make
dist". Even though we've been shipping the sha1collisiondetection
submodule[1] and using it by default if it's checked out[2] anyone
downloading git as a tarball would just get an empty
sha1collisiondetection/ directory.

Doing this automatically is a feature that's missing from git-archive,
but in the meantime let's bundle this up into the tarball we
ship. This ensures that the DC_SHA1_SUBMODULE flag does what's
intended even in an unpacked tarball, and more importantly means we're
building the exact same code from the same paths from git.git and from
the tarball.

I am not including all the files in the submodule, only the ones git
actually needs (and the licenses), only including some files like this
would be a useful feature if git-archive ever adds the ability to
bundle up submodules.

1. commit 86cfd61e6b ("sha1dc: optionally use sha1collisiondetection
   as a submodule", 2017-07-01)
2. cac87dc01d ("sha1collisiondetection: automatically enable when
   submodule is populated", 2017-07-01)

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---
 Makefile | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Makefile b/Makefile
index dc886f8eda..3955b02b6a 100644
--- a/Makefile
+++ b/Makefile

@@ -2643,6 +2643,21 @@ dist: git-archive$(X) configure
 		$(GIT_TARNAME)/configure \
 		$(GIT_TARNAME)/version \
 		$(GIT_TARNAME)/git-gui/version
+ifdef DC_SHA1_SUBMODULE
+	@mkdir -p $(GIT_TARNAME)/sha1collisiondetection/lib
+	@cp sha1collisiondetection/LICENSE.txt \
+		$(GIT_TARNAME)/sha1collisiondetection/
+	@cp sha1collisiondetection/LICENSE.txt \
+		$(GIT_TARNAME)/sha1collisiondetection/
+	@cp sha1collisiondetection/lib/sha1.[ch] \
+		$(GIT_TARNAME)/sha1collisiondetection/lib/
+	@cp sha1collisiondetection/lib/ubc_check.[ch] \
+		$(GIT_TARNAME)/sha1collisiondetection/lib/
+	$(TAR) rf $(GIT_TARNAME).tar \
+		$(GIT_TARNAME)/sha1collisiondetection/LICENSE.txt \
+		$(GIT_TARNAME)/sha1collisiondetection/lib/sha1.[ch] \
+		$(GIT_TARNAME)/sha1collisiondetection/lib/ubc_check.[ch]
+endif
 	@$(RM) -r $(GIT_TARNAME)
 	gzip -f -9 $(GIT_TARNAME).tar
 

-- 
2.15.1.424.g9478a66081