bug#53236: 26.1; encode-coding-string does not encode the string as expected

[Andreas Schwab]

On Jan 14 2022, Eli Zaretskii wrote:

>> From: Markus Triska <triska@metalevel.at>
>> Date: Thu, 13 Jan 2022 20:45:57 +0100
>> 
>> Correspondingly, I expect (encode-coding-string "\200" 'utf-8) to yield
>> a string equivalent to "\xC2\x80", but that seems not to be the case. I get:
>> 
>>     (encode-coding-string "\200" 'utf-8) --> "\200"
>> 
>> And therefore, unexpectedly:
>> 
>>     (string= (encode-coding-string "\200" 'utf-8) "\xC2\x80") --> nil
>
> "\200" is a unibyte string, and encoding unibyte strings returns those
> strings without changing them.
>
> This is not a bug, just a dark corner of encoding/decoding stuff.

Or a dark corner of the string syntax.

ELISP> (multibyte-string-p "\200")
nil
ELISP> (multibyte-string-p "\x80")
nil
ELISP> (multibyte-string-p "\x0080")
t
ELISP> (encode-coding-string "\x0080" 'utf-8)
"\302\200"

-- 
Andreas Schwab, schwab@linux-m68k.org
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