Cygwin fails to utilize Unicode replacement character

[Steven Penny]

On Tue, 4 Sep 2018 16:18:21, Thomas Wolff wrote:
> My vote is against the patch because the nodef glyph will often be just 
> blank space which is certainly worse than â–’.
> If conhost does not provide a reasonable way to enquire 0xFFFD 
> availability it's conhost's fault, not cygwin's so why should cygwin 
> implement a bad compromise. If conhost ever improves, cygwin can adapt.

This is some dangerous commentary. I would like to counter it now with some
actual research. Using BabelMap:

http://babelstone.co.uk/Software/BabelMap.html

You can do "Fonts", "Font Coverage" and you will get this result with code point
FFFD:

    yes: DejaVu Sans Mono

    no:
    - Consolas
    - Courier New
    - Lucida Console
    - MS Gothic
    - NSimSun
    - SimSun-ExtB

This is concerning true, but we can then review the ".notdef glyph" for the
problem fonts. As this glyph is not an actual character, i cant paste it here,
but i will describe them below:


    empty rectangle:
    - Courier New
    - Lucida Console
    - MS Gothic
    - SimSun-ExtB

    rectangle with a question mark inside: Consolas

    none: NSimSun

Note that I did not include "Raster Fonts", as it doesnt even allow multibyte
characters:

    $ printf '\xC2\xA1\n'
    sh: printf: write error: Permission denied


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