Fix byte-counting error in ‘format’

Problem reported by Paul Pogonyshev (Bug#38191).
* src/editfns.c (styled_format): When checking for adjacent
%-sequences, use byte position rather than character position.
* test/src/editfns-tests.el (format-properties): Test for fix.

2 files changed, 7 insertions, 3 deletions

diff --git a/src/editfns.c b/src/editfns.c
index 1b33f397110..8fc866d391f 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -3143,7 +3143,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
     /* The start and end bytepos in the output string.  */
     ptrdiff_t start, end;
 
-    /* The start of the spec in the format string.  */
+    /* The start bytepos of the spec in the format string.  */
     ptrdiff_t fbeg;
 
     /* Whether the argument is a string with intervals.  */
@@ -3954,7 +3954,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                     {
                       position++;
                       if (fieldn < nspec
-                          && position > info[fieldn].fbeg
+                          && bytepos >= info[fieldn].fbeg
                           && translated == info[fieldn].start)
                         {
                           translated += info[fieldn].end - info[fieldn].start;
@@ -3976,7 +3976,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
                     {
                       position++;
                       if (fieldn < nspec
-                          && position > info[fieldn].fbeg
+                          && bytepos >= info[fieldn].fbeg
                           && translated == info[fieldn].start)
                         {
                           translated += info[fieldn].end - info[fieldn].start;
diff --git a/test/src/editfns-tests.el b/test/src/editfns-tests.el
index a1060808f66..238fb409f0b 100644
--- a/test/src/editfns-tests.el
+++ b/test/src/editfns-tests.el
@@ -90,6 +90,10 @@
                                    (propertize "45" 'face 'italic)))
            #("012345    "
              0 2 (face bold) 2 4 (face underline) 4 10 (face italic))))
+  ;; Bug #38191
+  (should (ert-equal-including-properties
+           (format (propertize "‘foo’ %s bar" 'face 'bold) "xxx")
+           #("‘foo’ xxx bar" 0 13 (face bold))))
   ;; Bug #32404
   (should (ert-equal-including-properties
            (format (concat (propertize "%s" 'face 'bold)