Subject: Re: Fwd: Re: bug#28179: Fix use of string-to-multibyte in ispell.el

From: Reuben Thomas <[email-masked]>
Date: Thu, 24 Aug 2017 18:45:33 +0100

On 24/08/17 17:59, Eli Zaretskii wrote:
>> From: Reuben Thomas <[email-masked]>
>> Date: Wed, 23 Aug 2017 11:59:41 +0100
>>
>> I now understand the two meanings of "multibyte", but I don't understand
>> how my patch is deficient.
> I didn't say it was deficient,

Sorry, I was unclear. I meant, precisely, I don't see why you think my
patch's code returns a string that is not multibyte.

>  I asked whether you verified that
> either (a) the result is always multibyte

I believe I showed this is the case.

>
>> So in fact even when the string isn't copied (as in my patch, where I
>> also use a third argument of t to decode-coding-string) it appears to be
>> changed to a multibyte string.
> Fine, if you are sure, go ahead and push.
>

The reason I am asking again is because you first said:

> What if decode-coding-string returns a pure ASCII string, which is
> therefore unibyte?

and then later you said:

> The way I meant it, it has to do with the internal flag marking a
> string either unibyte or multibyte. Observe:
>   (multibyte-string-p "abcd") => nil
>
> but
>
>   (multibyte-string-p (decode-coding-string "abcd" 'utf-8)) => t

In other words:

1. As far as I can tell from the above (and my own confirmatory
experiments and reading of the documentation), a pure ASCII string can
be multibyte (it's a matter of the multibyte flag, not the number of
bytes used to store each character).

2. decode-coding-string always returns a multibyte string.

Since these two observations seemed to mean that you contradicted
yourself, I was checking whether in fact I had misunderstood (so that
for example one of my two observations above is wrong), or if your
original understanding was incomplete (so that in fact your question
about decode-coding-string is therefore misguided, because it can return
a pure ASCII unibyte string (in the coding sense) which is nonetheless a
multibyte string (in the sense that multibyte-string-p on it returns t).

Sorry about the miscommunication. In any case, I think the code is
correct, your original question was misguided, and I shall push, with,
as Noam requested in another message, an explanation of my  assumptions.
No need to reply further unless you think there really is a problem!

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