[Bug 60210] New: conhost: set_tty_attr() uses "\x1b[m" to reset foreground color to 7, inadvertently wiping the background color

[WineHQ Bugzilla]

http://bugs.winehq.org/show_bug.cgi?id=60210

            Bug ID: 60210
           Summary: conhost: set_tty_attr() uses "\x1b[m" to reset
                    foreground color to 7, inadvertently wiping the
                    background color
           Product: Wine
           Version: 9.0
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: -unknown
          Assignee: [e-mail]
          Reporter: [e-mail]
  Target Milestone: ---
      Distribution: ---

In programs/conhost/conhost.c, set_tty_attr() is responsible for converting
Win32 CHAR_INFO color attributes to ANSI escape sequences for tty output:

    if ((attr & 0x0f) != (console->tty_attr & 0x0f))
    {
        if ((attr & 0x0f) != 7)
        {
            ...
            sprintf(buf, "\x1b[%um", n);
            tty_write( console, buf, strlen(buf) );
        }
        else tty_write( console, "\x1b[m", 3 );
    }

When a console cell transitions from a colored foreground (e.g. 0x001B: Cyan on
Blue background) to default Light Gray text on the same non-black background
(0x0017: Light Gray on Blue background):
1. ((attr & 0x0f) != (console->tty_attr & 0x0f)) evaluates to true (7 != 11).
2. The 'else' branch executes and sends "\x1b[m".
3. In ANSI terminal emulation, "\x1b[m" (SGR 0) resets ALL attributes,
including the background color (resetting it to terminal default / black).
4. Next, the background check:
   if ((attr & 0xf0) != (console->tty_attr & 0xf0) && attr != 7)
   evaluates to false because both the current cell and console->tty_attr have
(attr & 0xf0) == BACKGROUND_BLUE (0x10).
5. As a result, conhost does not re-emit the background escape sequence (e.g.
"\x1b[44m").
6. console->tty_attr is updated to 0x0017.

Result:
The terminal background is reset to black by "\x1b[m", while conhost's internal
state tracker believes the terminal is still using BACKGROUND_BLUE. All
subsequent cells with attribute 0x0017 are rendered on a black background
instead of the requested blue background.

Expected behavior:
To reset only the foreground color without corrupting the background, conhost
should emit "\x1b[39m" (default foreground color) instead of "\x1b[m", or force
a background re-emission if (attr & 0xf0) != 0.

Original report: https://github.com/unxed/f4/issues/536

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