Re: bug#23750: 25.0.95; bug in url-retrieve or json.el

[Stefan Monnier]

> But when all the strings are either unibyte or pure-ASCII, we could
> produce a unibyte string without losing anything.

Actually, technically, if we take a multibyte string which only contains
pure-ASCII and convert it to unibyte, we lose information: with
a multibyte string, we can compare the `size` and the `size_byte`
fields, and if they're equal we know we have a pure-ASCII string,
whereas with a unibyte string, we'd have to scan the whole string
looking for a byte >= 128 to determine that it's pure-ASCII.

So maybe the change should be that when concat has to combine a unibyte
string and a multibyte string, it should first look to see if the
multibyte string has `size == size_byte` and if so, generate
a unibyte string.


        Stefan