Merge branch 'sg/travis-skip-identical-test'

Avoid repeatedly testing the same tree in TravisCI that have been
tested successfully already.

* sg/travis-skip-identical-test:
  travis-ci: record and skip successfully built trees
  travis-ci: create the cache directory early in the build process
  travis-ci: print the "tip of branch is exactly at tag" message in color

ci/lib-travisci.sh

@@ -16,18 +16,67 @@ 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
+}
+
 # Set 'exit on error' for all CI scripts to let the caller know that
 # 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

ci/run-linux32-docker.sh

@@ -22,3 +22,5 @@ docker run \
 	--volume "${HOME}/travis-cache:/tmp/travis-cache" \
 	daald/ubuntu32:xenial \
 	/usr/src/git/ci/run-linux32-build.sh $(id -u $USER)
+
+save_good_tree

ci/run-static-analysis.sh

@@ -6,3 +6,5 @@
 . ${0%/*}/lib-travisci.sh
 
 make coccicheck
+
+save_good_tree

ci/run-tests.sh

@@ -5,6 +5,7 @@
 
 . ${0%/*}/lib-travisci.sh
 
-mkdir -p $HOME/travis-cache
 ln -s $HOME/travis-cache/.prove t/.prove
 make --quiet test
+
+save_good_tree

ci/run-windows-build.sh

@@ -99,3 +99,5 @@ gfwci "action=log&buildId=$BUILD_ID" | cut -c 30-
 
 # Set exit code for TravisCI
 test "$RESULT" = "success"
+
+save_good_tree

ci/test-documentation.sh

@@ -25,3 +25,5 @@ sed '/^GIT_VERSION = / d' stderr.log
 ! test -s stderr.log
 test -s Documentation/git.html
 grep '<meta name="generator" content="Asciidoctor ' Documentation/git.html
+
+save_good_tree