[R] glimpse() errors if there is a UDF

[asfimport]

Using the example from ARROW-17437:

register_scalar_function(
  "test", 
  function(context, x) paste(x, collapse=","), 
  utf8(), 
  utf8(), 
  auto_convert=TRUE
)

Table$create(x = c("a", "b", "c")) |>
  transmute(test(x)) |>
  glimpse()

# Table (query)
# 3 rows x 1 columns
# Error in `dplyr::collect()`:
# ! NotImplemented: Call to R (resolve scalar user-defined function output data type) from a non-R thread from an unsupported context
# Run `rlang::last_error()` to see where the error occurred.

A variety of things could fix this:

• Supporting UDFs in any query (I think there's a draft PR open for this)
• The limit operator (FetchNode?) so that head() is handled in the ExecPlan and we don't need to use the RecordBatchReader workaround to get it efficiently (also PR in the works)
• Worse case, error more informatively

Reporter: Neal Richardson / @nealrichardson

Related issues:

• [R] Support head() in arrow_dplyr_query with user-defined function (duplicates)

_{Note: This issue was originally created as ARROW-17438. Please see the migration documentation for further details.}

[asfimport]

Will Jones / @wjones127:
I just tested, and this is now fixed. (I believe in ARROW-17178.) cc @paleolimbot  

[asfimport]

Dewey Dunnington / @paleolimbot:
Thanks Will! I just tested on master too...I think the lazy 'head' implementation did the trick here.

library(arrow, warn.conflicts = FALSE)
#> Some features are not enabled in this build of Arrow. Run `arrow_info()` for more information.
library(dplyr, warn.conflicts = FALSE)

register_scalar_function(
  "test", 
  function(context, x) paste(x, collapse=","), 
  utf8(), 
  utf8(), 
  auto_convert=TRUE
)

Table$create(x = c("a", "b", "c")) |>
  transmute(test(x)) |>
  glimpse()
#> Table (query)
#> 3 rows x 1 columns
#> $ `test(x)` <string> "a,b,c"
#> Call `print()` for query details