Cygwin fails to utilize Unicode replacement character

[Steven Penny]

On Sat, 1 Sep 2018 15:50:04, Doug Henderson wrote:
> This is an issue with rendering the character in the terminal window.
> In both the CMD/Conhost/bash and Mintty/bash terminals, I have
> configure the font to be Lucinda Console. This font does not have a
> glyph for U+FFFD: Replacement Character. (To check your character set,
> open Charmap, and check Advanced View. Type "Replacement Character" on
> the Search field, and search.) In the absence of that glyph, the
> terminal program must choose a glyph to display. In a later reply,
> Thomas Wolff, the maintainer of Mintty, indicates that Mintty displays
> the glyph for U+2592: Medium Shade (or a similar one). Without
> reference to the source, it is difficult to be certain, but Conhost
> appears to use a similar glyph.
>
> In Mintty, if you choose a font, such as DejaVu Sans Mono, which
> contains a glyph for U+FFFD: Replacement Character, you could expect
> to see that glyph, however that is determined by the terminal. As I
> write this, both Mintty (2.9.0) and Conhost (Windows 10 Home,
> 10.0.17134 Build 17134, fully patched) display a glyph with the
> appearance of U+2592 Medium Shade.

Hm, this is a tough call. These fonts come with Windows:

- Consolas
- Lucida Console

Neither of them provide U+FFFD, so that means it will fall back to the
".notdef glyph":

http://docs.microsoft.com/typography/opentype/spec/recom

That presents 2 options:

U+FFFD:
  unicode conformant:
    yes
  consolas or lucida console:
    invalid byte or missing char: same glyph

U+2592:
  unicode conformant:
    no
  consolas or lucida console:
    invalid byte or missing char: different glyph
    
I would prefer the first option - as other fonts do define U+FFFD, including
"DejaVu Sans Mono" which Cygwin provides via the "dejavu-fonts" package. However
I can understand if we wanted to side with people using one of the default
fonts.


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