Re: Bug in Unicode character width in Emacs 25.1, bisected to a761fbf (Unicode 9.0.0beta import)

[Eli Zaretskii]

> From: Ævar Arnfjörð Bjarmason <address@hidden>
> Date: Sun, 18 Sep 2016 20:52:44 +0200
> Cc: address@hidden, Eli Zaretskii <address@hidden>
> 
> [I'm sending this to the ML instead of bug-* because I figure a bug
> caused by the Unicode 9 import will garner some wider interest than
> your typical regression]

IMO, that was a mistake.  Bugs should be reported to the bug tracker,
and all those who might be interested are reading the bug mailing list
anyway.  Reporting a bug with "M-x report-emacs-bug" has the advantage
of including in the report important details about your system
configuration that might be relevant to the issue.

> The mu4e mode has a mu4e-use-fancy-chars option which if set will use
> e.g. ⚓ (Unicode ANCHOR; U+2693) instead of "a" in the vertically
> aligned headers view to show that an E-Mail has an attachment.
> 
> In Emacs 25.1 this vertical alignment is off consistent with ⚓ being
> considered a zero-width character, i.e. the content to the right-hand
> side of the ⚓ character is shifted 1 character to the left.

This character's width is 2, not zero:

  (char-width ?⚓) => 2

> I'm sorry that I don't have a more isolated test case than "run mu4e,
> turn on mu4e-use-fancy-chars and check out the misalignment in the
> header view" but I figure with the bisect + my successfully testing a
> revert of a761fbf on top of emacs-25.1 we have enough info to get
> started in narrowing this down.

Unfortunately, this description is not enough.  And since it is
unlikely we'll decide to revert that commit, we need more information
to understand what code (or font?) is the culprit and how to fix that.

For starters, I don't yet have a clear idea of what display problems
are caused by that character; a screenshot would help.  The results of
"C-u C-x =" with point on the anchor character would also be of value.

Finally, does selecting a different font for this character fix the
problem?

Thanks.