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.

2 files changed, 66 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)
diff --git a/tests/test-org-drill-cloze-regex-single-line.el b/tests/test-org-drill-cloze-regex-single-line.el
new file mode 100644
index 0000000..bd13269
--- /dev/null
+++ b/tests/test-org-drill-cloze-regex-single-line.el
@@ -0,0 +1,57 @@
+;;; test-org-drill-cloze-regex-single-line.el --- Regression for #38  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Upstream issue #38 (2021-01).  When `org-drill-use-visible-cloze-face-p'
+;; was non-nil, the cloze face leaked onto unrelated org headings.
+;; Root cause: the cloze regex's inner character class included
+;; `[:cntrl:]' / `[:space:]' which contain newline.  A stray `[' could
+;; match all the way to a `]' several lines later, covering org
+;; headings in between with the visible-cloze face.
+;;
+;; Fix: restrict the inner match to non-newline characters so a cloze
+;; stays within a single line — the intended scope.
+
+;;; Code:
+
+(require 'ert)
+(require 'org-drill)
+
+;;;; Regression — #38
+
+(ert-deftest test-cloze-regex-doesnt-span-newlines ()
+  "A `[' on one line followed by `]' two lines later should NOT match
+as a single cloze.  Pre-fix this matched the entire span, which is
+what caused the heading-face bleed."
+  (let ((re (org-drill--compute-cloze-regexp)))
+    (with-temp-buffer
+      (insert "Line one [some text\nLine two\nLine three] more")
+      (goto-char (point-min))
+      (should-not (re-search-forward re nil t)))))
+
+(ert-deftest test-cloze-regex-still-matches-single-line-cloze ()
+  "Single-line clozes still match — the fix doesn't break the happy path."
+  (let ((re (org-drill--compute-cloze-regexp)))
+    (with-temp-buffer
+      (insert "Capital of France is [Paris].")
+      (goto-char (point-min))
+      (should (re-search-forward re nil t))
+      (should (equal "[Paris]" (match-string 0))))))
+
+(ert-deftest test-cloze-regex-multiline-buffer-finds-only-line-bounded-cloze ()
+  "In a buffer with multiple lines and a single-line cloze on each,
+each cloze is matched independently — no spans across lines."
+  (let ((re (org-drill--compute-cloze-regexp)))
+    (with-temp-buffer
+      (insert "Line A: [foo]\n* Heading\nLine B: [bar]\n")
+      (goto-char (point-min))
+      (let ((matches nil))
+        (while (re-search-forward re nil t)
+          (push (match-string 0) matches))
+        (should (member "[foo]" matches))
+        (should (member "[bar]" matches))
+        ;; And exactly two matches — no spurious span across the heading.
+        (should (= 2 (length matches)))))))
+
+(provide 'test-org-drill-cloze-regex-single-line)
+
+;;; test-org-drill-cloze-regex-single-line.el ends here