R devel - Mar 2023 - tab-complete for non-syntactic names could attempt backtick-wrapping

Consider:

x <- list(`a b` = 1)
x$a<tab>

(i.e., press the 'tab' key after typing 'x$a')

The auto-complete mechanism will fill the buffer like so:
x$a b

This is not particularly helpful because this is now a syntax error.

It seems to me there's a simple fix -- in
utils:::specialCompletions(), we can wrap the result of
utils:::specialOpCompletionsHelper() with backticks for non-syntactic
names ([1]):

comps <- specialOpCompletionsHelper(op, suffix, prefix)
if (length(comps) == 0L) comps <- ""
+non_syntactic <- make.names(comps) != comps
+comps[non_syntactic] <- paste0("`", comps[non_syntactic],
"`")
sprintf("%s%s%s", prefix, op, comps)

I'm somewhat surprised this hasn't come up before (I searched for
'completeToken', 'specialCompletions', and
'specialOpCompletionsHelper' here and on Bugzilla), so I'm checking
with the list first if I'm missing anything before filing a patch.

Mike C

[1]
https://github.com/r-devel/r-svn/blob/4657f65a377cb5ef318c6548bc264e3b0f9517a0/src/library/utils/R/completion.R#L536-L538

? Wed, 1 Mar 2023 01:36:02 -0800
Michael Chirico via R-devel <r-devel at r-project.org> ?????:
> +comps[non_syntactic] <- paste0("`", comps[non_syntactic],
"`")
There are a few more corner cases. For example, comps could contain
backticks (which should be escaped with backslashes) and backslashes
(which should also be escaped). Thankfully, \uXXXX-style Unicode escape
sequences are not currently supported inside backticks, and "escape the
backslash" rule already takes care of them.

The deparse() function already knows these rules:

name <- 'hello world ` \\uFF'
cat(deparse1(as.name(name), backtick=TRUE), '\n')
# `hello world \` \\uFF`
`hello world \` \\uFF` <- 'hello'
`hello world \` \\uFF`
# [1] "hello"

-- 
Best regards,
Ivan