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bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "
From: |
Adam Porter |
Subject: |
bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg" |
Date: |
Fri, 27 May 2022 00:44:38 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 |
On 5/25/22 12:37, Eli Zaretskii wrote:
From: Visuwesh <visuweshm@gmail.com>
Cc: luangruo@yahoo.com, adam@alphapapa.net, 55623@debbugs.gnu.org
Date: Wed, 25 May 2022 22:52:00 +0530
How about the following instead then?
The 'default' face is always fully specified except in special cases
of TTY frames where :foreground and :background attributes may be
the strings "unspecified-bg" and "unspecified-bg" respectively to
mean to use the TTY's color for the foreground and background.
This is inaccurate and thus misleading. These special color names are
just like any other color names, they are "special" only when Emacs
needs to actually use them on the screen. For any other purposes,
they are just color names. Thus, the default face is "fully
specified" even when these colors are used. Also, these colors can be
used by other faces, not just by 'default'.
The code in question calls color-gradient on a face's foreground color,
using the default face as the fallback:
https://github.com/alphapapa/ement.el/blob/fd96491e82a5335058b72aaff7665f0a2c3d4495/ement-room-list.el#L201
(color-gradient
(color-name-to-rgb (face-foreground 'ement-room-list-very-recent
nil 'default))
(color-name-to-rgb (face-foreground 'ement-room-list-recent
nil 'default))
6)
When running on a TTY, face-foreground returns "unspecified-fg", which
causes color-name-to-rgb to return nil, which causes color-gradient to
signal an error.
Technically, these colors just tell Emacs not to emit a color-changing
command when it writes text to the screen, or emit a command that
tells the terminal driver "reset to your default color". But this is
an implementation detail, and we cannot talk about it in the manual
without explaining a lot of details about the inner workings of color
support on TTY frames.
Since the docstring says that the default face is always fully
specified, I thought that meant that the default face's foreground would
always have a defined, usable color name. Since "unspecified-fg" is not
in the manual, and apparently isn't usable by, e.g. color-name-to-rgb
(even on a graphical frame; and by "usable", I mean that it returns an
expected, useful color name), it seemed like an oversight in the manual
to not mention that string somewhere.
Theoretically, if "unspecified-fg" were documented somewhere, I could
have known that my code needs to account for it. I don't necessarily
need to know about the inner workings of color support on a TTY--only
that...
(face-foreground 'default)
...may return "unspecified-fg" rather than a specific color name, and
that, therefore...
(color-name-to-rgb (face-foreground 'default))
...may return nil rather than a color name.
I think a sentence or two in the appropriate place could clear this up
and prevent users like me from running into this problem. e.g.
Note that, on non-graphical frames, the default face's foreground and
background colors may be unspecified; in this case, those color names
may be the special values "unspecified-fg" and "unspecified-bg",
respectively. While these are in some senses legitimate color names
in Emacs, not all functions that expect color names as arguments may
handle these values as expected, so it may be necessary to check for
these special color names before calling such functions with them.
- bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg", Visuwesh, 2022/05/25
- bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg", Po Lu, 2022/05/25
- bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg", Visuwesh, 2022/05/25
- bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg", Eli Zaretskii, 2022/05/25
- bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg", Visuwesh, 2022/05/25
- bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg", Eli Zaretskii, 2022/05/25
- bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg", Visuwesh, 2022/05/25
- bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg", Eli Zaretskii, 2022/05/25
- bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg",
Adam Porter <=
- bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg", Eli Zaretskii, 2022/05/27
- bug#55623: 29.0.50; Mention that (face-foreground 'default) can return "unspecified-fg", Adam Porter, 2022/05/27