`distinct()` does not preserve attributes for `data.frame` objects

[thomasalcock]

According to the documentation distinct should preserve attributes for data.frame objects. Attributes are preserved for tibble objects, but not for data.frame objects. Package version: 1.0.7.

library(dplyr, warn.conflicts = FALSE)

df_noattr <- distinct(structure(iris, a="b"))
attr(df_noattr, "a", exact=TRUE)
# NULL

df_attr <- distinct(structure(as_tibble(iris), a="b"))
attr(df_attr, "a", exact=TRUE)
# "b"