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

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:


Duncan Murdoch

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