Don’t overwrite existing file if appending an empty data frame

[sbearrows]

Fixes tidyverse/readr#1408

Previously, if vroom_write() was supplied an empty data frame, vroom created an empty file without checking the value of append. But this meant data from the file could be deleted such as in this case.

library(vroom)
tf <- withr::local_tempfile()
data <- tibble::tibble(a = "1", b = "2", c = "3")

vroom_write(data, file = tf)
vroom(tf, show_col_types = FALSE)
#> # A tibble: 1 × 3
#>       a     b     c
#>   <dbl> <dbl> <dbl>
#> 1     1     2     3

vroom_write(data.frame(), file = tf, append = TRUE)
vroom(tf, show_col_types = FALSE)
#> # A tibble: 0 × 0

^{Created on 2022-07-15 by the reprex package (v2.0.1.9000)}

[jennybc]

I recommend turning off altrep / lazy reading in this test.

[sbearrows]

@jennybc I believe this is ready for another look!

[jennybc]

I can't see why we need to specify skip_empty_rows.

If we don't, let's remove it. In which case, the expectation can be come more compact.

[sbearrows]

We don't need it. I just wanted to make sure it wasn't writing an empty line when vroom_write(data.frame(), file = file, append = TRUE)

[jennybc]

I think if vroom_write(data.frame(), file = file, append = TRUE) wrote an empty line, that would be a bug and we would want to know about it. So I think the test is better without it (which I see has happened now).

[jennybc]

Nitpick:

let's remove it. In which case, the expectation can be come more compact.

There's still this.

[jennybc]

I made the expectation in the new test more similar to other in this file / package.

I added a NEWS bullet.