bug#38191: incorrect text properties in result of `format' with multibyte(?) characters

[Paul Eggert <eggert@cs.ucla.edu>]

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Thanks for reporting that. I installed the attached patch to fix it.

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From 63aafe766e7d81aa7b2e75bddf2ce3eca4611ae5 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 14 Nov 2019 14:42:39 -0800
Subject: [PATCH] =?UTF-8?q?Fix=20byte-counting=20error=20in=20=E2=80=98for?=
 =?UTF-8?q?mat=E2=80=99?=
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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.
---
 src/editfns.c             | 6 +++---
 test/src/editfns-tests.el | 4 ++++
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/editfns.c b/src/editfns.c
index 1b33f39711..8fc866d391 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 a1060808f6..238fb409f0 100644
--- a/test/src/editfns-tests.el
+++ b/test/src/editfns-tests.el
@@ -90,6 +90,10 @@ format-properties
                                    (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)
-- 
2.23.0