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

Great suggestion! I've started a patch:
https://bugs.r-project.org/show_bug.cgi?id=18479

On Wed, Mar 1, 2023 at 1:56 AM Ivan Krylov <krylov.r00t at gmail.com>
wrote:
>
> ? 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

There turn out to be a few more things to fix.

One problem is easy to solve: vapply() needs a third argument
specifying the type of the return value. (Can we have unit tests for
tab completion?)

The other problem is harder: `comps` defaults to an empty string, and
you can't have a symbol consisting of an empty string, because this
value is internally reserved for missing function arguments. I think
you can return(paste0(prefix, op)) if length(comps) == 0L, but this is
still somewhat worrying. R tries to prevent empty names, so I wouldn't
expect specialOpCompletionsHelper() to return an empty string, but I
can't prove it right now.

On the other hand, x$'a string' is the same as x$`a string`. Could we
just drop as.name() and keep the return value being a string literal?
I'm not sure about this, either.

-- 
Best regards,
Ivan