[PATCHv2 3/5] travis-ci: don't repeat the path of the cache directory

["SZEDER Gábor" <szeder.dev@gmail.com>]

Some of our 'ci/*' scripts repeat the name or full path of the Travis
CI cache directory, and the following patches will add new places
using that path.

Use a variable to refer to the path of the cache directory instead, so
it's hard-coded only in a single place.

Pay extra attention to the 32 bit Linux build: it runs in a Docker
container, so pass the path of the cache directory from the host to
the container in an environment variable.  Note that an environment
variable passed this way is exported inside the container, therefore
its value is directly available in the 'su' snippet even though that
snippet is single quoted.  Furthermore, use the variable in the
container only if it's been assigned a non-empty value, to prevent
errors when someone is running or debugging the Docker build locally,
because in that case the variable won't be set as there won't be any
Travis CI cache.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 ci/lib-travisci.sh       | 7 ++++---
 ci/run-linux32-build.sh  | 2 +-
 ci/run-linux32-docker.sh | 5 ++++-
 ci/run-tests.sh          | 3 ++-
 4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/ci/lib-travisci.sh b/ci/lib-travisci.sh
index 07f27c727..1efee55ef 100755
--- a/ci/lib-travisci.sh
+++ b/ci/lib-travisci.sh
@@ -21,8 +21,6 @@ skip_branch_tip_with_tag () {
 	fi
 }
 
-good_trees_file="$HOME/travis-cache/good-trees"
-
 # Save some info about the current commit's tree, so we can skip the build
 # job if we encounter the same tree again and can provide a useful info
 # message.
@@ -83,7 +81,10 @@ check_unignored_build_artifacts ()
 # and installing dependencies.
 set -ex
 
-mkdir -p "$HOME/travis-cache"
+cache_dir="$HOME/travis-cache"
+good_trees_file="$cache_dir/good-trees"
+
+mkdir -p "$cache_dir"
 
 skip_branch_tip_with_tag
 skip_good_tree
diff --git a/ci/run-linux32-build.sh b/ci/run-linux32-build.sh
index 248183982..d020b762c 100755
--- a/ci/run-linux32-build.sh
+++ b/ci/run-linux32-build.sh
@@ -28,7 +28,7 @@ test -z $HOST_UID || (CI_USER="ci" && useradd -u $HOST_UID $CI_USER)
 linux32 --32bit i386 su -m -l $CI_USER -c '
 	set -ex
 	cd /usr/src/git
-	ln -s /tmp/travis-cache/.prove t/.prove
+	test -n "$cache_dir" && ln -s "$cache_dir/.prove" t/.prove
 	make --jobs=2
 	make --quiet test
 '
diff --git a/ci/run-linux32-docker.sh b/ci/run-linux32-docker.sh
index 4f191c5bb..15288ea2c 100755
--- a/ci/run-linux32-docker.sh
+++ b/ci/run-linux32-docker.sh
@@ -11,6 +11,8 @@ docker pull daald/ubuntu32:xenial
 # $ docker run -itv "${PWD}:/usr/src/git" --entrypoint /bin/bash daald/ubuntu32:xenial
 # root@container:/# /usr/src/git/ci/run-linux32-build.sh
 
+container_cache_dir=/tmp/travis-cache
+
 docker run \
 	--interactive \
 	--env DEVELOPER \
@@ -18,8 +20,9 @@ docker run \
 	--env GIT_PROVE_OPTS \
 	--env GIT_TEST_OPTS \
 	--env GIT_TEST_CLONE_2GB \
+	--env cache_dir="$container_cache_dir" \
 	--volume "${PWD}:/usr/src/git" \
-	--volume "${HOME}/travis-cache:/tmp/travis-cache" \
+	--volume "$cache_dir:$container_cache_dir" \
 	daald/ubuntu32:xenial \
 	/usr/src/git/ci/run-linux32-build.sh $(id -u $USER)
 
diff --git a/ci/run-tests.sh b/ci/run-tests.sh
index 22355f009..deba73d9b 100755
--- a/ci/run-tests.sh
+++ b/ci/run-tests.sh
@@ -5,7 +5,8 @@
 
 . ${0%/*}/lib-travisci.sh
 
-ln -s $HOME/travis-cache/.prove t/.prove
+ln -s "$cache_dir/.prove" t/.prove
+
 make --quiet test
 
 check_unignored_build_artifacts
-- 
2.16.1.158.ge6451079d