using rowwise() on empty data.frames with list columns returns random booleans #7710
Description
When I use rowwise() on a zero-row tibble with a list column, and then compute something on that list column, the computing function gets fed randomly with either TRUE or FALSE, instead of always with with list().
library(dplyr)
#>
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#>
#> filter, lag
#> The following objects are masked from 'package:base':
#>
#> intersect, setdiff, setequal, union
tibble(a=list("test")) %>%
filter(a!="test") %>%
rowwise() %>%
# group_by(a) %>%
mutate(b=print(a))
#> [1] FALSE # <- this randomly is either TRUE or FALSE.
#> # A tibble: 0 × 2
#> # Rowwise:
#> # ℹ 2 variables: a <list>, b <lgl>Created on 2025-08-25 with reprex v2.1.1
When using group_by() instead, it works as expected:
library(dplyr)
#>
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#>
#> filter, lag
#> The following objects are masked from 'package:base':
#>
#> intersect, setdiff, setequal, union
tibble(a=list("test")) %>%
filter(a!="test") %>%
# rowwise() %>%
group_by(a) %>%
mutate(b=print(a))
#> list()
#> # A tibble: 0 × 2
#> # Groups: a [0]
#> # ℹ 2 variables: a <list>, b <list>Created on 2025-08-25 with reprex v2.1.1
This is with dplyr 1.1.4 and R version 4.5.1 (2025-06-13 ucrt)