On 31/01/2023 5:50 a.m., Martin Maechler wrote:
Tomas Kalibera
on Tue, 31 Jan 2023 10:53:21 +0100 writes:
> On 1/31/23 09:48, Ivan Krylov wrote:
>> Can we use the "bytes" encoding for such environment variables invalid
>> in the current locale? The following patch preserves CE_NATIVE for
>> strings valid in the current UTF-8 or multibyte locale (or
>> non-multibyte strings) but sets CE_BYTES for those that are invalid:
>>
>> Index: src/main/sysutils.c
>> ===================================================================
>> --- src/main/sysutils.c (revision 83731)
.....
>>
>> Here are the potential problems with this approach:
>>
>> * I don't know whether known_to_be_utf8 can disagree with utf8locale.
>> known_to_be_utf8 was the original condition for setting CE_UTF8 on
>> the string. I also need to detect non-UTF-8 multibyte locales, so
>> I'm checking for utf8locale and mbcslocale. Perhaps I should be more
>> careful and test for (enc == CE_UTF8) || (utf8locale && enc ==
>> CE_NATIVE) instead of just utf8locale.
>>
>> * I have verified that Sys.getenv() doesn't crash with UTF-8-invalid
>> strings in the environment with this patch applied, but now
>> print.Dlist does, because formatDL wants to compute the width of the
>> string which has the 'bytes' encoding. If this is a good way to
>> solve the problem, I can work on suggesting a fix for formatDL to
>> avoid the error.
> Thanks, indeed, type instability is a big problem of the approach "turn
> invalid strings to bytes". It is something what is historically being
> done in regular expression operations, but it is brittle and not user
> friendly: writing code to be agnostic to whether we are dealing with
> "bytes" or a regular string is very tedious. Pieces of type instability
> come also from that ASCII strings are always flagged "native" (never
> "bytes"). Last year I had to revert a big change which broke existing
> code by introducing some more of this instability due to better dealing
> with invalid strings in regular expressions. I've made some additions to
> R-devel allowing to better deal with such instability but it is still a
> pain and existing code has to be changed (and made more complicated).
> So, I don't think this is the way to go.
> Tomas
hmm.., that's a pity; I had hoped it was a pragmatic and valid strategy,
but of course you are right that type stability is really a
valid goal....
In general, what about behaving close to "old R" and replace all such
strings by NA_character_ (and typically raising one warning)?
This would keep the result a valid character vector, just with some NA entries.
Specifically for Sys.getenv(), I still think Simon has a very
valid point of "requiring" (of our design) that
Sys.getenv()[["BOOM"]] {double `[[`} should be the same as
Sys.getenv("BOOM")
Also, as typical R user, I'd definitely want to be able to get all the valid
environment variables, even if there are one or more invalid
ones. ... and similarly in other cases, it may be a cheap
strategy to replace invalid strings ("string" in the sense of
length 1 STRSXP, i.e., in R, a "character" of length 1) by
NA_character_ and keep all valid parts of the character vector
in a valid encoding.
- - - - - -
In addition to the above cheap "replace by NA"-strategy,
and at least once R is "all UTF-8", we could
also consider a more expensive strategy that would try to
replace invalid characters/byte-sequences by one specific valid UTF-8
character, i.e., glyph (think of a special version of "?") that
we would designate as replacement for "invalid-in-current-encoding".
Probably such a glyph already exists and we have seen it used in
some console's output when having to print such things.
I think it is U+FFFD, described here:
https://www.fileformat.info/info/unicode/char/fffd/index.htm
Duncan Murdoch
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