severe problems with composite characters

[Werner LEMBERG]

Kazu Yamamoto has reported the following two problems in the end of
July on the emacs-pretest-bug list which I repeat here so that more
people are reading his messages -- there were no replies.  AFAIK, they
are still valid with the current CVS.  Both problems are serious and
affect rendering of Thai at least in the mew mailing program.


    Werner

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string-width() returns a wrong number if its argument string
has composite characters.

Consider two bytes strings 0xcd 0xeb, whose width is one since they
are composed.

On Emacs 20.7 string-width() returns 1.
On Emacs 21.3.50 string-width() returns 2.

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Suppose that composite characters are stored to a file with a
multi-lingual coding-system. An example is TIS-620 characters with
UTF-8 (or ctext).

When Emacs reads the file, the composite characters are not composed
since there is no post-conv function associated to the multi-lingual
coding-system.

Is this a bug?