Suggestion: documentation and warnings specifying write_tsv assumes IANA spec

[ambevill]

Function write_tsv is the only write_* or format_* function that defaults to quote = 'none', and this is a recent behavior change (motivated by IANA considerations in #993 and #844 ). This default is an easy source of bugs for a naive user (e.g. me) that may have delim or eol characters in their content. (Tabs are explicitly forbidden by the IANA spec, but eol characters are also a problem for the same reason.)

So I would propose:

• Adding documentation explaining that write_tsv is intended for the IANA spec, and that many users should call it with quote = 'needed' or tend toward another writer, e.g. write_excel_csv(..., delim = '\t') if their data contains eol or delim characters.
• Adding a warning if vroom::vroom_format or vroom::vroom_write is called with quote = 'none' and the data contains eol or delim characters. (This task belongs in a vroom issue, not here. If this task is seriously considered then I will transfer it.)

I'm happy to create PRs for both, if given a greenlight.

Miscellaneous observations:

• Edition 1 stream_delim always behaves like quote = 'needed'. There is only an issue for edition 2 using vroom.
• Search for the quote_needed enum in the vroom package to find instances where the quoting logic is applied. This would be an ideal place to set a flag indicating that quotes were needed but disabled.

I don't think this needs a reprex, but here's a small test case:

library(dplyr)

# edition 1 always quotes as needed
readr::with_edition(1, {
  
  tibble(x = 'abc\tdef',
         z = 'abc\ndef') %>%
    readr::format_tsv('\t', quote = 'none') %>%
    readr::read_tsv()
  
})
# output: the tibble is correctly read

# edition 2 passes the quote argument to vroom
readr::with_edition(2, {
  
  tibble(x = 'abc\tdef',
         z = 'abc\ndef') %>%
    readr::format_tsv('\t', quote = 'none') %>%
    readr::read_tsv()
  
})
# output: the tibble is mangled

[pgramme]

I just had the same problem (I'm probably naive too) and would also be in favour of the warning.

Even if the TSV produced can be read properly by vroom, other tools like Excel, SAS, etc seem to not respect the IANA standard and will fail loading. Interoperability is supposed to be one of the strong arguments for using TSV and it can't be achieved here, so the warning makes sense imho