Re: make-glyph-code incompatibility

[Kim F. Storm]

Stefan Monnier <address@hidden> writes:

> The new make-glyph-code is a good change, but it introduces
> an incompatibility.  It seems that it makes previously working code
> fail silently.  Can we make it fail with an informative message?

The new encoding still merges a face id and char code into
an integer if the face id is < 64.  So an integer value may
still carry a face id in the upper bits.

Of course, I could make it always use a cons cell for non-default face.
Then we could check (and warn) if an integer value is >= 1^22, but
even if we do that, it can fail:

For example, how do you differentiate

    1 << 19 + ?a    (emacs 22 glyph code for 'a' in mode-line face)

and the unicode character with the same numeric value in emacs 23 ?

Also, issuing warnings during redisplay is a mess!


We introduced make-glyph-code in 22.1 in preparation for the unicode
merge in 23.1 - to give people time to adjust their code.

Perhaps emacs 23 NEWS file should repeat the description of make-glyph-code
from NEWS.22 - this time saying it is the only way to do it:


Maybe write something like (incompatible lisp changes):

** The functions `make-glyph-code', `glyph-char', and `glyph-face'
must be used to create and decode glyph codes in display tables.

The old method of creating a display table element by combining a face
number and a character code into a numeric glyph code is no longer
supported; using it may cause arbitrary characters and faces to be
displayed.

-- 
Kim F. Storm <address@hidden> http://www.cua.dk