Print a backtrace on unhandled errors in batch mode (Bug#44942).

* src/eval.c (signal_or_quit): Print a backtrace in batch mode if no
error handler was found.

* test/src/eval-tests.el (eval-tests/backtrace-in-batch-mode)
(eval-tests/backtrace-in-batch-mode/demoted-errors): New unit tests.

* etc/NEWS: Document change.

1 files changed, 33 insertions, 0 deletions

diff --git a/test/src/eval-tests.el b/test/src/eval-tests.el
index 074f5be1ef9..4125573dc6a 100644
--- a/test/src/eval-tests.el
+++ b/test/src/eval-tests.el
@@ -27,6 +27,7 @@
 
 (require 'ert)
 (eval-when-compile (require 'cl-lib))
+(require 'subr-x)
 
 (ert-deftest eval-tests--bug24673 ()
   "Check that Bug#24673 has been fixed."
@@ -176,4 +177,36 @@ in Common Lisp).  Instead, make sure substitution in backquote
 expressions works for identifiers starting with period."
   (should (equal (let ((.x 'identity)) (eval `(,.x 'ok))) 'ok)))
 
+(ert-deftest eval-tests/backtrace-in-batch-mode ()
+  (let ((emacs (expand-file-name invocation-name invocation-directory)))
+    (skip-unless (file-executable-p emacs))
+    (with-temp-buffer
+      (let ((status (call-process emacs nil t nil
+                                  "--quick" "--batch"
+                                  (concat "--eval="
+                                          (prin1-to-string
+                                           '(progn
+                                              (defun foo () (error "Boo"))
+                                              (foo)))))))
+        (should (natnump status))
+        (should-not (eql status 0)))
+      (goto-char (point-min))
+      (ert-info ((concat "Process output:\n" (buffer-string)))
+        (search-forward "  foo()")
+        (search-forward "  normal-top-level()")))))
+
+(ert-deftest eval-tests/backtrace-in-batch-mode/demoted-errors ()
+  (let ((emacs (expand-file-name invocation-name invocation-directory)))
+    (skip-unless (file-executable-p emacs))
+    (with-temp-buffer
+      (should (eql  0 (call-process emacs nil t nil
+                                    "--quick" "--batch"
+                                    (concat "--eval="
+                                            (prin1-to-string
+                                             '(with-demoted-errors "Error: %S"
+                                                (error "Boo")))))))
+      (goto-char (point-min))
+      (should (equal (string-trim (buffer-string))
+                     "Error: (error \"Boo\")")))))
+
 ;;; eval-tests.el ends here