Get bats_print_stack_trace() working

Line numbers and command excerpts were wrong, because the
stack-tracing magic has exceptions for tracing inside
BATS helper files. Added a workaround for this, such
that xrun and xpect will log the calling function.
Added excerpt and line-number tests.

Signed-off-by: Ed Santiago <santiago@redhat.com>

lib/bats-core/tracing.bash

@@ -1,13 +1,14 @@
 #!/usr/bin/env bash
 
 bats_capture_stack_trace() {
+	local internal_offset=${1:-0}
 	local test_file
 	local funcname
 	local i
 
 	BATS_STACK_TRACE=()
 
-	for ((i = 2; i != ${#FUNCNAME[@]}; ++i)); do
+	for ((i = $((2 + internal_offset)); i != ${#FUNCNAME[@]}; ++i)); do
 		# Use BATS_TEST_SOURCE if necessary to work around Bash < 4.4 bug whereby
 		# calling an exported function erases the test file's BASH_SOURCE entry.
 		test_file="${BASH_SOURCE[$i]:-$BATS_TEST_SOURCE}"
@@ -119,15 +120,26 @@ bats_trim_filename() {
 
 bats_debug_trap() {
 	# don't update the trace within library functions or we get backtraces from inside traps
-	if [[ "$1" != $BATS_ROOT/lib/* && "$1" != $BATS_ROOT/libexec/* ]]; then
-		# The last entry in the stack trace is not useful when en error occured:
-		# It is either duplicated (kinda correct) or has wrong line number (Bash < 4.4)
-		# Therefore we capture the stacktrace but use it only after the next debug
-		# trap fired.
-		# Expansion is required for empty arrays which otherwise error
-		BATS_CURRENT_STACK_TRACE=("${BATS_STACK_TRACE[@]+"${BATS_STACK_TRACE[@]}"}")
-		bats_capture_stack_trace
-	fi
+	local stack_trace_offset=
+	if [[ "$1" == $BATS_ROOT/lib/* || "$1" == $BATS_ROOT/libexec/* ]]; then
+        	if [[ "${FUNCNAME[1]}" != "xrun" && "${FUNCNAME[1]}" != "xpect" ]]; then
+			return
+                fi
+
+                # We are in xrun or xpect, which are internal functions that
+                # can throw test failures. Before they do, we need to make sure
+                # that we log the calling function (presumably in user's
+                # .bats file) so we can emit proper line numbers in messages.
+                stack_trace_offset=1
+        fi
+
+	# The last entry in the stack trace is not useful when en error occured:
+	# It is either duplicated (kinda correct) or has wrong line number (Bash < 4.4)
+	# Therefore we capture the stacktrace but use it only after the next debug
+	# trap fired.
+	# Expansion is required for empty arrays which otherwise error
+	BATS_CURRENT_STACK_TRACE=("${BATS_STACK_TRACE[@]+"${BATS_STACK_TRACE[@]}"}")
+	bats_capture_stack_trace $stack_trace_offset
 }
 
 # For some versions of Bash, the `ERR` trap may not always fire for every

test/xpect.bats

@@ -80,7 +80,9 @@ function _run_test() {
 
 @test "run: unexpected fail" {
   local -a commands=("xrun false")
-  _run_test "\[ rc=1 \(\*\* EXPECTED 0 \*\*\) \]" \
+  _run_test "\(in test file .*, line 2\)" \
+            "\`xrun false' failed" \
+            "\[ rc=1 \(\*\* EXPECTED 0 \*\*\) \]" \
             "/vvvvvvvvvvvvvv" \
             "\| FAIL: exit code is 1; expected 0"
 }
@@ -97,7 +99,8 @@ function _run_test() {
       'xrun echo abc'
       'xpect "cde"'
   )
-  _run_test "\`xrun echo abc' failed" \
+  _run_test "\(in test file .*\.bats, line 3\)" \
+            "\`xpect \"cde\"' failed" \
             "# run> echo abc" \
             "# abc" \
             "#\|     FAIL: output from 'echo abc'" \
@@ -107,10 +110,12 @@ function _run_test() {
 
 @test "xpect: mismatch, substring" {
   local -a commands=(
+      'true'
       'xrun echo abcdefg'
       'xpect "$output" =~ "ghi"'
   )
-  _run_test "\`xrun echo abcdefg' failed" \
+  _run_test "\(in test file .*\.bats, line 4\)" \
+            "\`xpect \"\\\$output\" =~ \"ghi\"' failed" \
             "# run> echo abcdefg" \
             "# abcdefg" \
             "#\|     FAIL: output from 'echo abcdefg'" \
@@ -132,7 +137,7 @@ function _run_test() {
       'xrun echo abc'
       'xpect "cde" "my test name"'
   )
-  _run_test "\`xrun echo abc' failed" \
+  _run_test "\`xpect \"cde\" \"my test name\"' failed" \
             "run> echo abc" \
             "# abc"\
             "#\|     FAIL: my test name" \