tests: optionally write results as JUnit-style .xml

This will come in handy when publishing the results of Git's test suite
during an automated Azure DevOps run.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

t/.gitignore

@@ -2,3 +2,4 @@
 /test-results
 /.prove
 /chainlinttmp
+/out/

t/test-lib.sh

@@ -321,6 +321,9 @@ do
 	-V|--verbose-log)
 		verbose_log=t
 		shift ;;
+	--write-junit-xml)
+		write_junit_xml=t
+		shift ;;
 	*)
 		echo "error: unknown test option '$1'" >&2; exit 1 ;;
 	esac
@@ -464,11 +467,24 @@ trap 'exit $?' INT
 # the test_expect_* functions instead.
 
 test_ok_ () {
+	if test -n "$write_junit_xml"
+	then
+		write_junit_xml_testcase "$*"
+	fi
 	test_success=$(($test_success + 1))
 	say_color "" "ok $test_count - $@"
 }
 
 test_failure_ () {
+	if test -n "$write_junit_xml"
+	then
+		junit_insert="<failure message=\"not ok $test_count -"
+		junit_insert="$junit_insert $(xml_attr_encode "$1")\">"
+		junit_insert="$junit_insert $(xml_attr_encode \
+			"$(printf '%s\n' "$@" | sed 1d)")"
+		junit_insert="$junit_insert</failure>"
+		write_junit_xml_testcase "$1" "      $junit_insert"
+	fi
 	test_failure=$(($test_failure + 1))
 	say_color error "not ok $test_count - $1"
 	shift
@@ -477,11 +493,19 @@ test_failure_ () {
 }
 
 test_known_broken_ok_ () {
+	if test -n "$write_junit_xml"
+	then
+		write_junit_xml_testcase "$* (breakage fixed)"
+	fi
 	test_fixed=$(($test_fixed+1))
 	say_color error "ok $test_count - $@ # TODO known breakage vanished"
 }
 
 test_known_broken_failure_ () {
+	if test -n "$write_junit_xml"
+	then
+		write_junit_xml_testcase "$* (known breakage)"
+	fi
 	test_broken=$(($test_broken+1))
 	say_color warn "not ok $test_count - $@ # TODO known breakage"
 }
@@ -739,6 +763,10 @@ test_start_ () {
 	test_count=$(($test_count+1))
 	maybe_setup_verbose
 	maybe_setup_valgrind
+	if test -n "$write_junit_xml"
+	then
+		junit_start=$(test-tool date getnanos)
+	fi
 }
 
 test_finish_ () {
@@ -776,6 +804,13 @@ test_skip () {
 
 	case "$to_skip" in
 	t)
+		if test -n "$write_junit_xml"
+		then
+			message="$(xml_attr_encode "$skipped_reason")"
+			write_junit_xml_testcase "$1" \
+				"      <skipped message=\"$message\" />"
+		fi
+
 		say_color skip >&3 "skipping test: $@"
 		say_color skip "ok $test_count # skip $1 ($skipped_reason)"
 		: true
@@ -791,9 +826,58 @@ test_at_end_hook_ () {
 	:
 }
 
+write_junit_xml () {
+	case "$1" in
+	--truncate)
+		>"$junit_xml_path"
+		junit_have_testcase=
+		shift
+		;;
+	esac
+	printf '%s\n' "$@" >>"$junit_xml_path"
+}
+
+xml_attr_encode () {
+	# We do not translate CR to &#x0d; because BSD sed does not handle
+	# \r in the regex. In practice, the output should not even have any
+	# carriage returns.
+	printf '%s\n' "$@" |
+	sed -e 's/&/\&amp;/g' -e "s/'/\&apos;/g" -e 's/"/\&quot;/g' \
+		-e 's/</\&lt;/g' -e 's/>/\&gt;/g' \
+		-e 's/	/\&#x09;/g' -e 's/$/\&#x0a;/' -e '$s/&#x0a;$//' |
+	tr -d '\012\015'
+}
+
+write_junit_xml_testcase () {
+	junit_attrs="name=\"$(xml_attr_encode "$this_test.$test_count $1")\""
+	shift
+	junit_attrs="$junit_attrs classname=\"$this_test\""
+	junit_attrs="$junit_attrs time=\"$(test-tool \
+		date getnanos $junit_start)\""
+	write_junit_xml "$(printf '%s\n' \
+		"    <testcase $junit_attrs>" "$@" "    </testcase>")"
+	junit_have_testcase=t
+}
+
 test_done () {
 	GIT_EXIT_OK=t
 
+	if test -n "$write_junit_xml" && test -n "$junit_xml_path"
+	then
+		test -n "$junit_have_testcase" || {
+			junit_start=$(test-tool date getnanos)
+			write_junit_xml_testcase "all tests skipped"
+		}
+
+		# adjust the overall time
+		junit_time=$(test-tool date getnanos $junit_suite_start)
+		sed "s/<testsuite [^>]*/& time=\"$junit_time\"/" \
+			<"$junit_xml_path" >"$junit_xml_path.new"
+		mv "$junit_xml_path.new" "$junit_xml_path"
+
+		write_junit_xml "  </testsuite>" "</testsuites>"
+	fi
+
 	if test -z "$HARNESS_ACTIVE"
 	then
 		test_results_dir="$TEST_OUTPUT_DIRECTORY/test-results"
@@ -1034,6 +1118,7 @@ then
 else
 	mkdir -p "$TRASH_DIRECTORY"
 fi
+
 # Use -P to resolve symlinks in our working directory so that the cwd
 # in subprocesses like git equals our $PWD (for pathname comparisons).
 cd -P "$TRASH_DIRECTORY" || exit 1
@@ -1047,6 +1132,19 @@ then
 	test_done
 fi
 
+if test -n "$write_junit_xml"
+then
+	junit_xml_dir="$TEST_OUTPUT_DIRECTORY/out"
+	mkdir -p "$junit_xml_dir"
+	junit_xml_base=${0##*/}
+	junit_xml_path="$junit_xml_dir/TEST-${junit_xml_base%.sh}.xml"
+	junit_attrs="name=\"${junit_xml_base%.sh}\""
+	junit_attrs="$junit_attrs timestamp=\"$(TZ=UTC \
+		date +%Y-%m-%dT%H:%M:%S)\""
+	write_junit_xml --truncate "<testsuites>" "  <testsuite $junit_attrs>"
+	junit_suite_start=$(test-tool date getnanos)
+fi
+
 # Provide an implementation of the 'yes' utility
 yes () {
 	if test $# = 0