fix: keep cloze regex within a single line (upstream #38)

The inner match was [[:cntrl:][:graph:][:space:]]+?, which silently
includes newline.  A stray [ could match all the way to a ]
several lines later, covering org headings in between with the
visible-cloze face.  Reporter saw lines 4 and 5 of test.org lose
their org-level-N face and use default instead.

Switched the inner class to [^\n]+?.  Clozes now stay within a
single line, which matches the design intent and stops the face
bleed.  Three new tests cover the regression.

1 files changed, 9 insertions, 2 deletions

diff --git a/org-drill.el b/org-drill.el
index 6885791..b628695 100644
--- a/org-drill.el
+++ b/org-drill.el
@@ -231,10 +231,17 @@ Mature items are due for review, but are not new."
   "Delimiter in cloze expression for hints.")
 
 (defun org-drill--compute-cloze-regexp ()
-  "Return a regexp that detects clozes."
+  "Return a regexp that detects clozes.
+
+The inner match is constrained to non-newline characters so a cloze
+stays within one line.  An older version used
+`[[:cntrl:][:graph:][:space:]]' which silently included newline,
+letting a stray `[' match all the way to a `]' several lines later
+and bleeding the cloze face onto intervening org headings (upstream
+issue #38)."
   (concat "\\("
           (regexp-quote org-drill-left-cloze-delimiter)
-          "[[:cntrl:][:graph:][:space:]]+?\\)\\(\\|"
+          "[^\n]+?\\)\\(\\|"
           (regexp-quote org-drill-hint-separator)
           ".+?\\)\\("
           (regexp-quote org-drill-right-cloze-delimiter)