[gdb/build, c++20] Fix UTF-8 string literal usage

PR build/33675 reports a build breaker:
...
top.c: In function ‘void box_one_message(ui_file*, std::string, int)’:
top.c:1368:35: error: conditional expression between distinct pointer types \
  ‘const char8_t*’ and ‘const char*’ lacks a cast
 1368 |   const char *wall = emojis_ok () ? u8"\u2503" : "|";
      |                      ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
...

The problem is that UTF-8 string literals have type:
- const char[N]    (until C++20), or
- const char8_t[N] (since C++20)

Fix this by assigning to variables:
...
static const char bd_heavy_vertical[] = u8"\u2503";
...
and using the variables instead.

Tested by rebuilding on x86_64-linux, and starting gdb and checking the
welcome message box.

Reviewed-By: Guinevere Larsen <guinevere@redhat.com>
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33675

diff --git a/gdb/top.c b/gdb/top.c
index 2e3b373d5e2f150ba0a6ec9e29d0172729e46a9b..0798fea7a3bbfbbea6ac192c6ca9a15ebeb30d0e 100644 (file)
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -1359,13 +1359,25 @@ There is NO WARRANTY, to the extent permitted by law.",
     }
 }
 
+/* Unicode Block “Box Drawing” chars.  UTF-8 string literals have type:
+   - const char[N]    (until C++20), or
+   - const char8_t[N] (since C++20).
+   Assign them to a variable to stabilize the type.
+*/
+static const char bd_heavy_horizontal[] = u8"\u2501";
+static const char bd_heavy_vertical[] = u8"\u2503";
+static const char bd_heavy_down_and_right[] = u8"\u250f";
+static const char bd_heavy_down_and_left[] = u8"\u2513";
+static const char bd_heavy_up_and_right[] = u8"\u2517";
+static const char bd_heavy_up_and_left[] = u8"\u251b";
+
 /* Print MESSAGE to STREAM in lines of maximum size WIDTH, so that it fits
    in an ascii art box of width WIDTH+4.  Messages may be broken on
    spaces.  */
 static void
 box_one_message (ui_file *stream, std::string message, int width)
 {
-  const char *wall = emojis_ok () ? u8"\u2503" : "|";
+  const char *wall = emojis_ok () ? bd_heavy_vertical : "|";
   while (!message.empty ())
     {
       std::string line;
@@ -1444,10 +1456,10 @@ print_gdb_hints (struct ui_file *stream)
 
       if (emojis_ok ())
        {
-         gdb_printf (stream, u8"\u250f");
+         gdb_printf (stream, "%s", bd_heavy_down_and_right);
          for (int i = 0; i < (width - 2); i++)
-           gdb_printf (stream, u8"\u2501");
-         gdb_printf (stream, u8"\u2513\n");
+           gdb_printf (stream, "%s", bd_heavy_horizontal);
+         gdb_printf (stream, "%s\n", bd_heavy_down_and_left);
        }
       else
        gdb_printf (stream, "+%s+\n", sep.c_str ());
@@ -1457,10 +1469,10 @@ print_gdb_hints (struct ui_file *stream)
 
       if (emojis_ok ())
        {
-         gdb_printf (stream, u8"\u2517");
+         gdb_printf (stream, "%s", bd_heavy_up_and_right);
          for (int i = 0; i < (width - 2); i++)
-           gdb_printf (stream, u8"\u2501");
-         gdb_printf (stream, u8"\u251b\n");
+           gdb_printf (stream, "%s", bd_heavy_horizontal);
+         gdb_printf (stream, "%s\n", bd_heavy_up_and_left);
        }
       else
        gdb_printf (stream, "+%s+\n", sep.c_str ());