Fix handling of newlines when converting quotes

[krlmlr]

I remember using deparse(parse()) to avoid edge cases like '\\\''. The non-obvious gsub() really seems like the simplest solution to ensure we always match one character after each backslash.

Closes #551.

[lorenzwalthert]

Awesome, thanks. This is much more elegant and even more general than #553. I am always afraid of gsub() / grep() with escape characters 😨. Maybe now is the time to overcome that? Then maybe you can tell me why do all three paterns match?

grepl("\n", "\n")
#> [1] TRUE
grepl("\\n", "\n")
#> [1] TRUE
grepl("\\\n", "\n")
#> [1] TRUE

^{Created on 2019-10-11 by the reprex package (v0.3.0)}

[michaelquinn32]

Thank you!!!

[krlmlr]

"\n" matches because it's a literal newline character.

"\\n" matches because backslashes are treated specially in regex -- and backslash + n happens to match a newline.

"\\\n" -- 🤕 it seems that backslash + \n also matches a newline. It's true for both perl = TRUE and perl = FALSE, so seems reliable. Also this means that we can seek for answers in a broader context.

Luckily, it breaks with the fourth backslash.

grepl("\\\\n", "\n")
#> [1] FALSE

^{Created on 2019-10-13 by the reprex package (v0.3.0)}

[lorenzwalthert]

Thanks Kirill.