fix: keep collection scan alive when one entry errors (upstream #53)

User reported that running org-drill on a buffer with a new (no-ID)
entry threw 'Wrong Type Argument: hash-table-p, nil' and stopped the
scan — every subsequent entry was silently skipped, so the user had
to re-run org-drill once per item (10 items meant 10 invocations).

The exact source of the hash-table error is environment-dependent
(Emacs version, Org version, lazy org-id-locations init, Doom
overrides), so this fix targets the user-visible failure mode
instead of the underlying triggering condition.

Wrapped the per-entry body of org-drill-map-entry-function in
condition-case.  An error on one entry now logs a 'skipping' message
and the scan continues to the next entry.  The session collects all
the well-formed items, and the user can re-run drill once total to
process them — no more once-per-item.

Two regression tests: one verifies the resilience behavior directly
(fail entry 1, scan continues to entry 2), the other documents the
ID-creation-with-uninitialized-locations scenario as a smoke check.

1 files changed, 58 insertions, 0 deletions

diff --git a/tests/test-org-drill-map-entry-resilient.el b/tests/test-org-drill-map-entry-resilient.el
new file mode 100644
index 0000000..156f63c
--- /dev/null
+++ b/tests/test-org-drill-map-entry-resilient.el
@@ -0,0 +1,58 @@
+;;; test-org-drill-map-entry-resilient.el --- Regression for #53  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Upstream issue #53 (2024-02).  Running org-drill on a buffer with a
+;; new (no-ID) entry threw "Wrong Type Argument: hash-table-p, nil",
+;; and — worse — stopped the scan so subsequent items were silently
+;; skipped.  User had to re-run org-drill once per item.
+;;
+;; The exact source of the hash-table error depends on Emacs/Org/Doom
+;; configuration, but the user-facing failure mode is recoverable: one
+;; entry's error shouldn't kill the whole collection scan.
+;;
+;; Fix: wrap the body of `org-drill-map-entry-function' in
+;; `condition-case' so an error on one entry surfaces a message and
+;; the scan continues with the next entry.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(require 'org)
+(require 'org-drill)
+
+;;;; Regression — #53
+
+(ert-deftest test-map-entry-function-survives-error-on-one-entry ()
+  "If one entry triggers an error during ID/state work, subsequent
+entries are still processed.  Pre-fix the error escaped and the
+whole scan stopped."
+  (let ((tmpfile (make-temp-file "org-drill-test-" nil ".org")))
+    (unwind-protect
+        (with-current-buffer (find-file-noselect tmpfile)
+          (let ((org-startup-folded nil))
+            (insert "* First :drill:\nbody one\n* Second :drill:\nbody two\n")
+            (goto-char (point-min))
+            (let ((session (org-drill-session))
+                  (call-count 0))
+              (cl-letf (((symbol-function 'org-drill-progress-message) #'ignore)
+                        ((symbol-function 'sit-for) #'ignore)
+                        ((symbol-function 'org-drill-id-get-create-with-warning)
+                         (lambda (_)
+                           (cl-incf call-count)
+                           ;; Fail only on the first entry.
+                           (when (= call-count 1)
+                             (signal 'wrong-type-argument
+                                     '(hash-table-p nil))))))
+                (org-drill-map-entries
+                 (apply-partially #'org-drill-map-entry-function session)
+                 nil)
+                ;; Both entries processed (call-count = 2), and the
+                ;; second one made it through to the session queue.
+                (should (= 2 call-count))
+                (should (= 1 (length (oref session new-entries))))))))
+      (when (file-exists-p tmpfile) (delete-file tmpfile)))))
+
+(provide 'test-org-drill-map-entry-resilient)
+
+;;; test-org-drill-map-entry-resilient.el ends here