Handle "empty line" regexp in xref searches

* lisp/progmodes/xref.el (xref--collect-matches-1): Stop after one
match if re-search-forward doesn't move point (bug#23426).

* test/automated/xref-tests.el
(xref-collect-matches-finds-an-empty-line-regexp-match):
Uncomment test.

2 files changed, 12 insertions, 8 deletions

diff --git a/lisp/progmodes/xref.el b/lisp/progmodes/xref.el
index 540c7b0e925..62cef235988 100644
--- a/lisp/progmodes/xref.el
+++ b/lisp/progmodes/xref.el
@@ -1016,7 +1016,11 @@ directory, used as the root of the ignore globs."
     (syntax-propertize line-end)
     ;; FIXME: This results in several lines with the same
     ;; summary. Solve with composite pattern?
-    (while (re-search-forward regexp line-end t)
+    (while (and
+            ;; REGEXP might match an empty string.  Or line.
+            (or (null matches)
+                (> (point) line-beg))
+            (re-search-forward regexp line-end t))
       (let* ((beg-column (- (match-beginning 0) line-beg))
              (end-column (- (match-end 0) line-beg))
              (loc (xref-make-file-location file line beg-column))
diff --git a/test/automated/xref-tests.el b/test/automated/xref-tests.el
index 1b500c3c418..28ca3511c22 100644
--- a/test/automated/xref-tests.el
+++ b/test/automated/xref-tests.el
@@ -28,10 +28,10 @@
     (should (equal 0 (xref-file-location-column (nth 0 locs))))
     (should (equal 4 (xref-file-location-column (nth 1 locs))))))
 
-;; (ert-deftest xref-collect-matches-finds-an-empty-line-regexp-match ()
-;;   (let* ((matches (xref-collect-matches "^$" "*" xref-tests-data-dir nil))
-;;          (locs (mapcar #'xref-item-location matches)))
-;;     (should (= 1 (length matches)))
-;;     (should (string-match-p "file2\\.txt\\'" (xref-location-group (nth 0 locs))))
-;;     (should (equal 1 (xref-location-line (nth 0 locs))))
-;;     (should (equal 0 (xref-file-location-column (nth 0 locs))))))
+(ert-deftest xref-collect-matches-finds-an-empty-line-regexp-match ()
+  (let* ((matches (xref-collect-matches "^$" "*" xref-tests-data-dir nil))
+         (locs (mapcar #'xref-item-location matches)))
+    (should (= 1 (length matches)))
+    (should (string-match-p "file2\\.txt\\'" (xref-location-group (nth 0 locs))))
+    (should (equal 1 (xref-location-line (nth 0 locs))))
+    (should (equal 0 (xref-file-location-column (nth 0 locs))))))