[PATCH v3] [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 apparently 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 and x86_64-freebsd.

Reported-By: wuzy01@qq.com

PR tui/28800
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28800
---
 gdb/charset.c                            |  20 +++++
 gdb/charset.h                            |   7 ++
 gdb/testsuite/gdb.tui/unicode-prompt.exp |  71 ++++++++++++++++
 gdb/tui/tui-io.c                         | 100 +++++++++++++++++++----
 4 files changed, 183 insertions(+), 15 deletions(-)
 create mode 100644 gdb/testsuite/gdb.tui/unicode-prompt.exp

diff --git a/gdb/charset.c b/gdb/charset.c
index 259362563b2..9c0df83c0d3 100644
--- a/gdb/charset.c
+++ b/gdb/charset.c
@@ -690,6 +690,26 @@ wchar_iterator::iterate (enum wchar_iterate_result *out_result,
   return -1;
 }
 
+/* See charset.h.  */
+
+void
+wchar_iterator::skip (size_t len)
+{
+  m_input += len;
+
+  gdb_assert (len <= m_bytes);
+  m_bytes -= len;
+}
+
+/* See charset.h.  */
+
+void
+wchar_iterator::reset (const gdb_byte *input, size_t bytes)
+{
+  m_input = input;
+  m_bytes = bytes;
+}
+
 struct charset_vector
 {
   ~charset_vector ()
diff --git a/gdb/charset.h b/gdb/charset.h
index a0f109da5ee..4d68e61f35a 100644
--- a/gdb/charset.h
+++ b/gdb/charset.h
@@ -126,6 +126,13 @@ class wchar_iterator
   int iterate (enum wchar_iterate_result *out_result, gdb_wchar_t **out_chars,
 	       const gdb_byte **ptr, size_t *len);
 
+  /* Increase the input buffer pointer by LEN bytes.  */
+  void skip (size_t len);
+
+  /* Reset the input buffer pointer to INPUT and the number of bytes in the
+     input buffer to BYTES.  */
+  void reset (const gdb_byte *input, size_t bytes);
+
  private:
 
   /* The underlying iconv descriptor.  */
diff --git a/gdb/testsuite/gdb.tui/unicode-prompt.exp b/gdb/testsuite/gdb.tui/unicode-prompt.exp
new file mode 100644
index 00000000000..ac2b6202c04
--- /dev/null
+++ b/gdb/testsuite/gdb.tui/unicode-prompt.exp
@@ -0,0 +1,71 @@
+# Copyright 2025 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) } {
+    # Override "C" settings from default_gdb_init.
+    setenv LC_ALL "C.UTF-8"
+
+    Term::clean_restart 24 80
+}
+
+if {![Term::enter_tui]} {
+    unsupported "TUI not supported"
+    return
+}
+
+set unicode_char "\u276F"
+set unicode_char_unsupported "❯"
+
+set color_on [string cat {\033} "\[" "31m"]
+set color_off [string cat {\033} "\[" "0m"]
+
+set prompt "GDB$color_on$unicode_char$color_off "
+set prompt_no_color "GDB$unicode_char "
+set prompt_no_color_re [string_to_regexp $prompt_no_color]
+
+if { [ishost *-*-*bsd*] } {
+    set issue_eol "\r\n"
+} else {
+    set issue_eol "\n"
+}
+
+# Set new prompt.
+send_gdb "set prompt $prompt$issue_eol"
+# Set old prompt back.
+send_gdb "set prompt (gdb) $issue_eol"
+
+gdb_assert \
+    { [Term::wait_for "^${prompt_no_color_re}set prompt $gdb_prompt "] } \
+    "prompt with unicode char"
+
+set line [Term::get_line_with_attrs [expr $Term::_cur_row - 1]]
+verbose -log "line with attrs: '$line'"
+
+set prompt_with_attrs_re "GDB<fg:red>$unicode_char<fg:default> "
+set prompt_unsupported_re "GDB$unicode_char_unsupported "
+
+set test "colored unicode char"
+if { [regexp "^${prompt_with_attrs_re}set prompt .*$" $line] } {
+    pass $test
+} elseif { [regexp "^${prompt_unsupported_re}set prompt .*$" $line] } {
+    # I get this on freebsd: no color, and unicode char not recognized.
+    unsupported $test
+} else {
+    fail $test
+}
diff --git a/gdb/tui/tui-io.c b/gdb/tui/tui-io.c
index 1b4cc82cce8..5c39e42362a 100644
--- a/gdb/tui/tui-io.c
+++ b/gdb/tui/tui-io.c
@@ -45,6 +45,7 @@
 #include "gdbsupport/unordered_map.h"
 #include "pager.h"
 #include "gdbsupport/gdb-checked-static-cast.h"
+#include "charset.h"
 
 /* This redefines CTRL if it is not already defined, so it must come
    after terminal state related include files like <term.h> and
@@ -539,30 +540,99 @@ tui_puts_internal (WINDOW *w, const char *string, int *height)
   char c;
   int prev_col = 0;
   bool saw_nl = false;
+  size_t skip = 0;
+  wchar_iterator it ((gdb_byte *)string, strlen (string), host_charset (), 1);
 
-  while ((c = *string++) != 0)
+  while (true)
     {
-      if (c == '\1' || c == '\2')
-	{
-	  /* Ignore these, they are readline escape-marking
-	     sequences.  */
-	  continue;
-	}
+      bool handled = false;
+
+      /* Get iterator in sync with string.  */
+      it.skip (skip);
+      skip = 0;
+
+      /* Detect and handle multibyte chars.  */
+      {
+	enum wchar_iterate_result res2;
+	gdb_wchar_t *dummy1;
+	const gdb_byte *dummy2;
+	size_t len;
+	int res = it.iterate (&res2, &dummy1, &dummy2, &len);
+	if (res < 0)
+	  {
+	    /* End of string.  */
+	    gdb_assert (res2 == wchar_iterate_eof);
+	    break;
+	  }
+
+	if (res == 0)
+	  {
+	    if (res2 == wchar_iterate_invalid)
+	      {
+		/* Let single-byte char code handle it.  */
+		gdb_assert (len == 1);
+	      }
+	    else if (res2 == wchar_iterate_incomplete)
+	      {
+		/* Iterator has been setup to return end-of-string on next
+		   call to iterate.  Make that an advance-by-one instead, and
+		   let single-byte char code handle it.  */
+		it.reset ((gdb_byte *)(string + 1), strlen (string + 1));
+	      }
+	    else
+	      gdb_assert_not_reached ("");
+	  }
+	else
+	  {
+	    /* res > 0.  */
+	    gdb_assert (res2 == wchar_iterate_ok);
+	    if (len > 1)
+	      {
+		/* Multi-byte char.  Handle it.  */
+		waddnstr (w, string, len);
+		string += len;
+		handled = true;
+	      }
+	    else
+	      {
+		/* Single-byte char.  Let single-byte char code handle it.  */
+		gdb_assert (len == 1);
+	      }
+	  }
+      }
 
-      if (c == '\033')
+      if (!handled)
 	{
-	  size_t bytes_read = apply_ansi_escape (w, string - 1);
-	  if (bytes_read > 0)
+	  c = *string++;
+	  if (c == '\0')
+	    {
+	      /* End of string.  */
+	      break;
+	    }
+
+	  if (c == '\1' || c == '\2')
 	    {
-	      string = string + bytes_read - 1;
+	      /* Ignore these, they are readline escape-marking
+		 sequences.  */
 	      continue;
 	    }
-	}
 
-      if (c == '\n')
-	saw_nl = true;
+	  if (c == '\033')
+	    {
+	      size_t bytes_read = apply_ansi_escape (w, string - 1);
+	      if (bytes_read > 0)
+		{
+		  skip = bytes_read - 1;
+		  string += skip;
+		  continue;
+		}
+	    }
+
+	  if (c == '\n')
+	    saw_nl = true;
 
-      do_tui_putc (w, c);
+	  do_tui_putc (w, c);
+	}
 
       if (height != nullptr)
 	{

base-commit: 87f5e2edca1412326ae40489e2780821093481cb
-- 
2.43.0