Quote variable names when reporting on repair

[jennybc]

When set_tidy_names() reports names affected by repair, they should be quoted in the message.

tibble::tidy_names(c("a", "", "b", "a"))
#> New names:
#> a -> a..1
#>  -> ..2
#> a -> a..4
#> [1] "a..1" "..2"  "b"    "a..4"

Created on 2018-05-02 by the reprex package (v0.2.0).

Written quickly as an aside during a meeting with @hadley, now fleshed out a bit. Let me know if I/we should expand.

[krlmlr]

Thanks. Do we need to quote all names, or only non-syntactic ones?

[hadley]

Also need to display NAs

tibble::tidy_names(c("", NA))
#> New names:
#>  -> ..1
#>  -> ..2
#> [1] "..1" "..2"

And in general, needs to encode strings:

tibble::tidy_names(c("\n", "\n"))
#> New names:
#> 
#>  -> 
#> ..1
#> 
#>  -> 
#> ..2
#> [1] "\n..1" "\n..2"

[krlmlr]

Will add tests as part of #406.