Improve error message when a function is supplied quoted to funs()

[lionel-]

See r-lib/rlang#411:

library("dplyr")
packageVersion("dplyr")
# [1] ‘0.7.4’
packageVersion("rlang")
# [1] ‘0.2.0’
mp <- c("cyl" = "cylinders", "gear" = "gears")
rename_at(.tbl = datasets::mtcars, 
          .vars = names(mp), 
          .funs = funs(function(si) { mp[si] }))
# Error: All arguments must be named 

[lionel-]

Or should we treat quoted functions specially? The UI of funs() is weird because it supports calls as in funs(my_function(.)) and symbols as in funs(my_function). The latter might suggest you should be able to pass a lambda function as well, e.g. funs(function(x) do(x)). It might make the UI a bit more predictable if we special-case calls to function.

I think ideally funs() would only support calls and not symbols then there would be no ambiguity. Of course this is now too late to change.

cc @JohnMount @hadley

[hadley]

I think we need to rework/replace funs with a version that does not quote, but instead accepts purrr style anonymous functions. I've been trying to teach funs() and it's currently just too confusing.

[lock]

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