[PATCH] [gdb/tui] Handle unicode chars in prompt

[Tom de Vries <tdevries@suse.de>]

Let's try to set the prompt using a unicode character, say '❯', aka U+276F
(heavy right-pointing angle quotation mark ornament).

This works fine on an xterm with CLI (with X marking the position of the
blinking cursor):
...
$ gdb -q -ex "set prompt GDB❯ "
GDB❯ X
...
but with TUI:
...
$ gdb -q -tui -ex "set prompt GDB❯ "
...
we get instead:
...
GDB  GDB  X
...

We can use the test-case gdb.tui/unicode-prompt.exp to get more details, using
tuiterm.

With Term::dump_screen we have:
...
   16 (gdb) set prompt GDB❯
   17 GDB❯ GDB❯ GDB❯ set prompt (gdb)
   18 (gdb)
...
and with Term::dump_screen_with_attrs (summarizing using attribute sets <attrs1>
and <attrs2>):
...
   16 (gdb) set prompt GDB❯
   17 GDB<attrs1>❯<attrs2> GDB<attrs1>❯<attrs2> GDB<attrs1>❯<attrs2> set prompt (gdb)
   18 (gdb)
...
where:
...
<attrs1> == <reverse:1><invisible:1><blinking:1><intensity:bold>
<attrs2> == <reverse:0><invisible:0><blinking:0><intensity:normal>
...

This explains why we didn't see the unicode char on xterm: it's hidden
because the invisible attribute is set.

So, there seem to be two problems:
- the attributes are incorrect, and
- the prompt is repeated a couple of times.

In TUI, the prompt is written out by tui_puts_internal, which outputs one byte
at a time using waddch, which apparantly breaks multi-byte char support.

Fix this by detecting multi-byte chars in tui_puts_internal, and printing them using
waddnstr.

Tested on x86_64-linux.

Reported-By: wuzy01@qq.com

PR tui/28800
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28800
---
 gdb/testsuite/gdb.tui/unicode-prompt.exp | 45 ++++++++++++++++
 gdb/tui/tui-io.c                         | 67 +++++++++++++++++++++++-
 2 files changed, 111 insertions(+), 1 deletion(-)
 create mode 100644 gdb/testsuite/gdb.tui/unicode-prompt.exp

diff --git a/gdb/testsuite/gdb.tui/unicode-prompt.exp b/gdb/testsuite/gdb.tui/unicode-prompt.exp
new file mode 100644
index 00000000000..6c2f9036921
--- /dev/null
+++ b/gdb/testsuite/gdb.tui/unicode-prompt.exp
@@ -0,0 +1,45 @@
+# Copyright 2023 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+require allow_tui_tests
+
+tuiterm_env
+
+save_vars { env(LC_ALL) env(LANG) env(LC_CTYPE) } {
+    # Override "C" settings from default_gdb_init.
+    setenv LC_ALL ""
+    setenv LANG en_US.UTF-8
+    setenv LC_CTYPE ""
+
+    Term::clean_restart 24 80
+
+    if {![Term::enter_tui]} {
+	unsupported "TUI not supported"
+	return
+    }
+
+    set unicode_char "\u276F"
+
+    set prompt "GDB$unicode_char "
+    set prompt_re [string_to_regexp $prompt]
+
+    # Set new prompt.
+    send_gdb "set prompt $prompt\n"
+    # Set old prompt back.
+    send_gdb "set prompt (gdb) \n"
+
+    gdb_assert { [Term::wait_for "^${prompt_re}set prompt $gdb_prompt "] } \
+	"prompt with unicode char"
+}
diff --git a/gdb/tui/tui-io.c b/gdb/tui/tui-io.c
index a1eadcd937d..f6412e2dbad 100644
--- a/gdb/tui/tui-io.c
+++ b/gdb/tui/tui-io.c
@@ -514,6 +514,51 @@ tui_puts (const char *string, WINDOW *w)
     update_cmdwin_start_line ();
 }
 
+/* Return true if STRING starts with a multi-byte char.  Return the length of
+   the multi-byte char in LEN, or 0 in case it's a multi-byte null char.
+   Implementation based on _rl_read_mbchar.  */
+
+static bool
+is_mb_char (const char *string, int &len)
+{
+  for (len = 1; len <= MB_CUR_MAX; len++)
+    {
+      size_t res;
+
+      {
+	wchar_t wc;
+	mbstate_t ps;
+	memset (&ps, 0, sizeof (mbstate_t));
+	res = mbrtowc (&wc, string, len, &ps);
+      }
+
+      if (res == (size_t)(-1))
+	{
+	  /* Not a multi-byte char.  */
+	  return false;
+	}
+
+      if (res == (size_t)(-2))
+	{
+	  /* Part of a multi-byte char.  */
+	  continue;
+	}
+
+      if (res == 0)
+	{
+	  /* Multi-byte null char.  */
+	  len = 0;
+	  return true;
+	}
+
+      /* Complete multi-byte char.  */
+      gdb_assert (res == len);
+      return true;
+    }
+
+  return false;
+}
+
 static void
 tui_puts_internal (WINDOW *w, const char *string, int *height)
 {
@@ -521,8 +566,28 @@ tui_puts_internal (WINDOW *w, const char *string, int *height)
   int prev_col = 0;
   bool saw_nl = false;
 
-  while ((c = *string++) != 0)
+  while (true)
     {
+      {
+	int mb_len;
+	if (is_mb_char (string, mb_len) && mb_len != 1)
+	  {
+	    if (mb_len == 0)
+	      {
+		/* Multi-byte null char.  */
+		break;
+	      }
+
+	    waddnstr (w, string, mb_len);
+	    string += mb_len;
+	    continue;
+	  }
+      }
+
+      c = *string++;
+      if (c == '\0')
+	break;
+
       if (c == '\n')
 	saw_nl = true;
 

base-commit: 5fd6b60d86ab6ab4bbd173524062b5d2aeac199a
-- 
2.35.3