8 files changed, 103 insertions, 5 deletions
diff --git a/ci/lib-travisci.sh b/ci/lib-travisci.sh
index 331d3eb3a..07f27c727 100755
--- a/ci/lib-travisci.sh
+++ b/ci/lib-travisci.sh
@@ -16,16 +16,77 @@ skip_branch_tip_with_tag () {
 	if TAG=$(git describe --exact-match "$TRAVIS_BRANCH" 2>/dev/null) &&
 		test "$TAG" != "$TRAVIS_BRANCH"
 	then
-		echo "Tip of $TRAVIS_BRANCH is exactly at $TAG"
+		echo "$(tput setaf 2)Tip of $TRAVIS_BRANCH is exactly at $TAG$(tput sgr0)"
 		exit 0
 	fi
 }
 
+good_trees_file="$HOME/travis-cache/good-trees"
+
+# Save some info about the current commit's tree, so we can skip the build
+# job if we encounter the same tree again and can provide a useful info
+# message.
+save_good_tree () {
+	echo "$(git rev-parse $TRAVIS_COMMIT^{tree}) $TRAVIS_COMMIT $TRAVIS_JOB_NUMBER $TRAVIS_JOB_ID" >>"$good_trees_file"
+	# limit the file size
+	tail -1000 "$good_trees_file" >"$good_trees_file".tmp
+	mv "$good_trees_file".tmp "$good_trees_file"
+}
+
+# Skip the build job if the same tree has already been built and tested
+# successfully before (e.g. because the branch got rebased, changing only
+# the commit messages).
+skip_good_tree () {
+	if ! good_tree_info="$(grep "^$(git rev-parse $TRAVIS_COMMIT^{tree}) " "$good_trees_file")"
+	then
+		# Haven't seen this tree yet, or no cached good trees file yet.
+		# Continue the build job.
+		return
+	fi
+
+	echo "$good_tree_info" | {
+		read tree prev_good_commit prev_good_job_number prev_good_job_id
+
+		if test "$TRAVIS_JOB_ID" = "$prev_good_job_id"
+		then
+			cat <<-EOF
+			$(tput setaf 2)Skipping build job for commit $TRAVIS_COMMIT.$(tput sgr0)
+			This commit has already been built and tested successfully by this build job.
+			To force a re-build delete the branch's cache and then hit 'Restart job'.
+			EOF
+		else
+			cat <<-EOF
+			$(tput setaf 2)Skipping build job for commit $TRAVIS_COMMIT.$(tput sgr0)
+			This commit's tree has already been built and tested successfully in build job $prev_good_job_number for commit $prev_good_commit.
+			The log of that build job is available at https://travis-ci.org/$TRAVIS_REPO_SLUG/jobs/$prev_good_job_id
+			To force a re-build delete the branch's cache and then hit 'Restart job'.
+			EOF
+		fi
+	}
+
+	exit 0
+}
+
+check_unignored_build_artifacts ()
+{
+	! git ls-files --other --exclude-standard --error-unmatch \
+		-- ':/*' 2>/dev/null ||
+	{
+		echo "$(tput setaf 1)error: found unignored build artifacts$(tput sgr0)"
+		false
+	}
+}
+
 # Set 'exit on error' for all CI scripts to let the caller know that
-# something went wrong
+# something went wrong.
+# Set tracing executed commands, primarily setting environment variables
+# and installing dependencies.
 set -ex
 
+mkdir -p "$HOME/travis-cache"
+
 skip_branch_tip_with_tag
+skip_good_tree
 
 if test -z "$jobname"
 then
@@ -48,8 +109,8 @@ linux-clang|linux-gcc)
 	export LINUX_P4_VERSION="16.2"
 	export LINUX_GIT_LFS_VERSION="1.5.2"
 
-	P4_PATH="$(pwd)/custom/p4"
-	GIT_LFS_PATH="$(pwd)/custom/git-lfs"
+	P4_PATH="$HOME/custom/p4"
+	GIT_LFS_PATH="$HOME/custom/git-lfs"
 	export PATH="$GIT_LFS_PATH:$P4_PATH:$PATH"
 	;;
 osx-clang|osx-gcc)
diff --git a/ci/print-test-failures.sh b/ci/print-test-failures.sh
index 8c8973cbf..4f261ddc0 100755
--- a/ci/print-test-failures.sh
+++ b/ci/print-test-failures.sh
@@ -5,6 +5,15 @@
 
 . ${0%/*}/lib-travisci.sh
 
+# Tracing executed commands would produce too much noise in the loop below.
+set +x
+
+if ! ls t/test-results/*.exit >/dev/null 2>/dev/null
+then
+	echo "Build job failed before the tests could have been run"
+	exit
+fi
+
 for TEST_EXIT in t/test-results/*.exit
 do
 	if [ "$(cat "$TEST_EXIT")" != "0" ]
diff --git a/ci/run-linux32-build.sh b/ci/run-linux32-build.sh
index e30fb2cdd..c19c50c1c 100755
--- a/ci/run-linux32-build.sh
+++ b/ci/run-linux32-build.sh
@@ -6,6 +6,8 @@
 #   run-linux32-build.sh [host-user-id]
 #
 
+set -x
+
 # Update packages to the latest available versions
 linux32 --32bit i386 sh -c '
     apt update >/dev/null &&
@@ -25,6 +27,7 @@ test -z $HOST_UID || (CI_USER="ci" && useradd -u $HOST_UID $CI_USER) &&
 # Build and test
 linux32 --32bit i386 su -m -l $CI_USER -c '
     cd /usr/src/git &&
+    ln -s /tmp/travis-cache/.prove t/.prove &&
     make --jobs=2 &&
     make --quiet test
 '
diff --git a/ci/run-linux32-docker.sh b/ci/run-linux32-docker.sh
index 0edf63acf..4f191c5bb 100755
--- a/ci/run-linux32-docker.sh
+++ b/ci/run-linux32-docker.sh
@@ -19,5 +19,10 @@ docker run \
 	--env GIT_TEST_OPTS \
 	--env GIT_TEST_CLONE_2GB \
 	--volume "${PWD}:/usr/src/git" \
+	--volume "${HOME}/travis-cache:/tmp/travis-cache" \
 	daald/ubuntu32:xenial \
 	/usr/src/git/ci/run-linux32-build.sh $(id -u $USER)
+
+check_unignored_build_artifacts
+
+save_good_tree
diff --git a/ci/run-static-analysis.sh b/ci/run-static-analysis.sh
index 68dd0f080..fe4ee4e06 100755
--- a/ci/run-static-analysis.sh
+++ b/ci/run-static-analysis.sh
@@ -6,3 +6,5 @@
 . ${0%/*}/lib-travisci.sh
 
 make coccicheck
+
+save_good_tree
diff --git a/ci/run-tests.sh b/ci/run-tests.sh
index f0c743de9..22355f009 100755
--- a/ci/run-tests.sh
+++ b/ci/run-tests.sh
@@ -5,6 +5,9 @@
 
 . ${0%/*}/lib-travisci.sh
 
-mkdir -p $HOME/travis-cache
 ln -s $HOME/travis-cache/.prove t/.prove
 make --quiet test
+
+check_unignored_build_artifacts
+
+save_good_tree
diff --git a/ci/run-windows-build.sh b/ci/run-windows-build.sh
index 8757b3a97..d99a180e5 100755
--- a/ci/run-windows-build.sh
+++ b/ci/run-windows-build.sh
@@ -69,6 +69,10 @@ esac
 
 echo "Visual Studio Team Services Build #${BUILD_ID}"
 
+# Tracing execued commands would produce too much noise in the waiting
+# loop below.
+set +x
+
 # Wait until build job finished
 STATUS=
 RESULT=
@@ -90,7 +94,10 @@ done
 # Print log
 echo ""
 echo ""
+set -x
 gfwci "action=log&buildId=$BUILD_ID" | cut -c 30-
 
 # Set exit code for TravisCI
 test "$RESULT" = "success"
+
+save_good_tree
diff --git a/ci/test-documentation.sh b/ci/test-documentation.sh
index 7a0a848e8..a20de9ca1 100755
--- a/ci/test-documentation.sh
+++ b/ci/test-documentation.sh
@@ -18,6 +18,9 @@ test -s Documentation/git.xml
 test -s Documentation/git.1
 grep '<meta name="generator" content="AsciiDoc ' Documentation/git.html
 
+rm -f stdout.log stderr.log
+check_unignored_build_artifacts
+
 # Build docs with AsciiDoctor
 make clean
 make --jobs=2 USE_ASCIIDOCTOR=1 doc > >(tee stdout.log) 2> >(tee stderr.log >&2)
@@ -25,3 +28,8 @@ sed '/^GIT_VERSION = / d' stderr.log
 ! test -s stderr.log
 test -s Documentation/git.html
 grep '<meta name="generator" content="Asciidoctor ' Documentation/git.html
+
+rm -f stdout.log stderr.log
+check_unignored_build_artifacts
+
+save_good_tree