tests: when run in Bash, annotate test failures with file name/line number

When a test fails, it is nice to see where the corresponding code lives
in the worktree. Sadly, it seems that only Bash allows us to infer this
information. Let's do it when we detect that we're running in a Bash.

This will come in handy in the next commit, where we teach the GitHub
Actions workflow to annotate failed test runs with this information.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Đoàn Trần Công Danh <congdanhqx@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib.sh

@@ -642,6 +642,18 @@ die () {
 	fi
 }
 
+file_lineno () {
+	test -z "$GIT_TEST_FRAMEWORK_SELFTEST" && test -n "$BASH" || return 0
+	local i
+	for i in ${!BASH_SOURCE[*]}
+	do
+		case $i,"${BASH_SOURCE[$i]##*/}" in
+		0,t[0-9]*.sh) echo "t/${BASH_SOURCE[$i]}:$LINENO: ${1+$1: }"; return;;
+		*,t[0-9]*.sh) echo "t/${BASH_SOURCE[$i]}:${BASH_LINENO[$(($i-1))]}: ${1+$1: }"; return;;
+		esac
+	done
+}
+
 GIT_EXIT_OK=
 trap 'die' EXIT
 # Disable '-x' tracing, because with some shells, notably dash, it
@@ -687,7 +699,7 @@ test_failure_ () {
 		write_junit_xml_testcase "$1" "      $junit_insert"
 	fi
 	test_failure=$(($test_failure + 1))
-	say_color error "not ok $test_count - $1"
+	say_color error "$(file_lineno error)not ok $test_count - $1"
 	shift
 	printf '%s\n' "$*" | sed -e 's/^/#	/'
 	test "$immediate" = "" || { finalize_junit_xml; GIT_EXIT_OK=t; exit 1; }