bug#42904: [PATCH] Non-Unicode frame title crashes Emacs on macOS

["Mattias Engdegård" <mattiase@acm.org>]

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21 aug. 2020 kl. 15.26 skrev Eli Zaretskii <eliz@gnu.org>:

> That is true, but str_as_multibyte simply interprets any valid UTF-8
> sequence as a character, and any invalid sequence as a raw bytes.  I
> thought this was precisely what you wanted for this use case, no?

Sorry, I read the comment for that function and got the impression that it would interpret raw bytes as Latin-1. Fortunately that wasn't true, and using it seems to be a clear improvement. Now a mixture of non-ASCII and raw bytes, like "a\377büc" results in the title "a��büc", which is one � too many but good enough.

What about the attached patch then? Only tested on macOS, admittedly.


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From dbe9ee59a179a3d42f337c60b5f426f6ff2913ca Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Fri, 21 Aug 2020 16:09:04 +0200
Subject: [PATCH] Always make a multibyte string for the frame title
 (bug#42904)

* src/xdisp.c (gui_consider_frame_title): Multibyte-encode any raw
bytes in the title, and then pass a multibyte string to the back-end
for use as a frame title.  This cuts down a little on the rubbish
shown when raw bytes sneak in by mistake (as part of the buffer name,
for instance).
---
 src/xdisp.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index ad03ac4605..9eeae43a52 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -12482,6 +12482,11 @@ gui_consider_frame_title (Lisp_Object frame)
       display_mode_element (&it, 0, -1, -1, fmt, Qnil, false);
       len = MODE_LINE_NOPROP_LEN (title_start);
       title = mode_line_noprop_buf + title_start;
+      /* Make sure any raw bytes in the title are properly
+         multibyte-encoded.  */
+      ptrdiff_t nchars = 0;
+      len = str_as_multibyte (title, mode_line_noprop_buf_end - title,
+                              len, &nchars);
       unbind_to (count, Qnil);
 
       /* Set the title only if it's changed.  This avoids consing in
@@ -12493,9 +12498,10 @@ gui_consider_frame_title (Lisp_Object frame)
            || SBYTES (f->name) != len
            || memcmp (title, SDATA (f->name), len) != 0)
           && FRAME_TERMINAL (f)->implicit_set_name_hook)
-	FRAME_TERMINAL (f)->implicit_set_name_hook (f,
-                                                    make_string (title, len),
-                                                    Qnil);
+        {
+          Lisp_Object title_string = make_multibyte_string (title, nchars, len);
+          FRAME_TERMINAL (f)->implicit_set_name_hook (f, title_string, Qnil);
+        }
     }
 }
 
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