Add a testcase for bug#42360

	* test/src/comp-tests.el (comp-test-42360): New testcase.

	* test/src/comp-test-funcs.el (comp-test-42360-f): New function.

2 files changed, 52 insertions, 0 deletions

diff --git a/test/src/comp-test-funcs.el b/test/src/comp-test-funcs.el
index 2fe6276227a..fe9943a1b91 100644
--- a/test/src/comp-test-funcs.el
+++ b/test/src/comp-test-funcs.el
@@ -290,6 +290,53 @@
   (declare (speed -1))
   3)
 
+(defun comp-test-42360-f (str end-column
+                              &optional start-column padding ellipsis
+                              ellipsis-text-property)
+  ;; From `truncate-string-to-width'.  A large enough function to
+  ;; potentially use all registers and that is modifying local
+  ;; variables inside condition-case.
+  (let ((str-len (length str))
+        (str-width 14)
+        (ellipsis-width 3)
+        (idx 0)
+        (column 0)
+        (head-padding "") (tail-padding "")
+        ch last-column last-idx from-idx)
+    (condition-case nil
+        (while (< column start-column)
+          (setq ch (aref str idx)
+                column (+ column (char-width ch))
+                idx (1+ idx)))
+      (args-out-of-range (setq idx str-len)))
+    (if (< column start-column)
+        (if padding (make-string end-column padding) "")
+      (when (and padding (> column start-column))
+        (setq head-padding (make-string (- column start-column) padding)))
+      (setq from-idx idx)
+      (when (>= end-column column)
+        (condition-case nil
+            (while (< column end-column)
+              (setq last-column column
+                    last-idx idx
+                    ch (aref str idx)
+                    column (+ column (char-width ch))
+                    idx (1+ idx)))
+          (args-out-of-range (setq idx str-len)))
+        (when (> column end-column)
+          (setq column last-column
+                idx last-idx))
+        (when (and padding (< column end-column))
+          (setq tail-padding (make-string (- end-column column) padding))))
+      (if (and ellipsis-text-property
+               (not (equal ellipsis ""))
+               idx)
+          (concat head-padding
+                  (substring str from-idx idx)
+                  (propertize (substring str idx) 'display (or ellipsis "")))
+        (concat head-padding (substring str from-idx idx)
+                tail-padding ellipsis)))))
+
 
 ;;;;;;;;;;;;;;;;;;;;
 ;; Tromey's tests ;;
diff --git a/test/src/comp-tests.el b/test/src/comp-tests.el
index 8f0b90f8e01..092504565a6 100644
--- a/test/src/comp-tests.el
+++ b/test/src/comp-tests.el
@@ -363,6 +363,11 @@ https://lists.gnu.org/archive/html/bug-gnu-emacs/2020-03/msg00914.html."
   (should (= (comp-test-speed--1-f) 3))
   (should-not (subr-native-elisp-p (symbol-function #'comp-test-speed--1-f))))
 
+(ert-deftest comp-test-42360 ()
+  "<https://lists.gnu.org/archive/html/bug-gnu-emacs/2020-07/msg00418.html>."
+  (should (string= (comp-test-42360-f "Nel mezzo del " 18 0 32 "yyy" nil)
+                   "Nel mezzo del     yyy")))
+
 
 ;;;;;;;;;;;;;;;;;;;;;
 ;; Tromey's tests. ;;