Capture `{cli}` output for reporting - r

Question

I would like to capture the dynamic output produced by {cli} to use in error reporting/logging.
Here's an example:
my_function <- function(val, return_message = TRUE) {
if(val == 'a'){
if (return_message) cli::cli_alert("your value {val} = a!")
} else {
if (return_message) cli::cli_alert("your value {val} is not equal to a!")
}
if (return_message) cli::cli_h2("processing now complete")
return(val)
}
Using my_function, it returns val and also prints a message that is dynamic, based on the input value:
→ your value x is not equal to a!
── processing now complete ──
[1] "x"
Is there any way to capture the dynamic output from {cli} functions, ideally by appending to a list or a similar method?
Ideal output would be something like this:
my_data <- list(val = "x", message = c("your value x is not equal to a!", "processing now complete"))

Answer 1

I don't think cli_X() returns the text, but you could imagine a wrapper that might do what you want. Consider this as a start:
cli_wrapper <- function(str, type="alert", return_str = TRUE, return_message=TRUE, ...){
str <- with(list(...), glue::glue(str))
if(return_message){
cmd <- glue::glue('cli::cli_{type}("{str}")')
eval(parse(text=cmd))
}
if(return_str){
invisible(str)
}
}
In the function above, return_message indicates whether the cli_X() function should be run and the return_str indicates whether the string should be returned (invisibly). You could then rewrite your function with the cli_wrapper() function:
my_function <- function(val, return_message = TRUE) {
message <- NULL
if(val == 'a'){
message <- c(message, cli_wrapper("your value {val} = a!", type="alert", val = val, return_message = return_messasge))
}else{
message <- c(message, cli_wrapper("your value {val} is not equal to a!", type="alert", val = val, return_message = return_messasge))
}
message <- c(message, cli_wrapper("processing now complete", type="h2", return_message = return_messasge))
ret <- list(val=val, message = message)
invisible(ret)
}
Running the function a couple of different ways would give the following output:
my_data <- my_function(val="x", return_message=TRUE)
# → your value x is not equal to a!
#
# ── processing now complete ──
#
my_data
# $val
# [1] "x"
#
# $message
# [1] "your value x is not equal to a!" "processing now complete"
#
my_data <- my_function(val="x", return_message=FALSE)
my_data
# $val
# [1] "x"
#
# $message
# [1] "your value x is not equal to a!" "processing now complete"

Answer 2

{cli} provides a utility function cli_fmt() which gives a much easier interface for this behaviour.
# Function to test `cli_fmt()`
noisy_identity <- function(x) {
cli::cli_h1("Noisily returning {.val {x}}")
cli::cli_bullets(c(
"*" = "Here",
"*" = "are",
"*" = "some",
"*" = "bulllets!"
))
x
}
# This just returns `"hi"` and prints a bunch of text
noisy_identity("hi")
#>
#> ── Noisily returning "hi" ──────────────────────────────────────────────────────
#> • Here
#> • are
#> • some
#> • bulllets!
#> [1] "hi"
# Wrapping in `cli_fmt()` means only the message is returned
cli::cli_fmt(noisy_identity("hi"))
#> [1] ""
#> [2] "── Noisily returning \"hi\" ──────────────────────────────────────────────────────"
#> [3] "• Here"
#> [4] "• are"
#> [5] "• some"
#> [6] "• bulllets!"
# We can use this to define a function that modifies other functions so that
# they return both output value *and* messages produced like so:
capture_cli_messages <- function(fun) {
function(..., .quiet = TRUE) {
output <- list(result = NULL, messages = NULL)
output$messages <- cli::cli_fmt({
output$result <- fun(...)
})
if (!.quiet) cat(output$messages, sep = "\n")
output
}
}
# `capture_cli_messages()` modifies the behaviour of `noisy_identity()`
noisy_identity2 <- capture_cli_messages(noisy_identity)
noisy_identity2("hi")
#> $result
#> [1] "hi"
#>
#> $messages
#> [1] ""
#> [2] "── Noisily returning \"hi\" ──────────────────────────────────────────────────────"
#> [3] "• Here"
#> [4] "• are"
#> [5] "• some"
#> [6] "• bulllets!"
# The .quiet argument can be used if you still want to print the messages out
noisy_identity2("hi", .quiet = FALSE)
#>
#> ── Noisily returning "hi" ──────────────────────────────────────────────────────
#> • Here
#> • are
#> • some
#> • bulllets!
#> $result
#> [1] "hi"
#>
#> $messages
#> [1] ""
#> [2] "── Noisily returning \"hi\" ──────────────────────────────────────────────────────"
#> [3] "• Here"
#> [4] "• are"
#> [5] "• some"
#> [6] "• bulllets!"
Created on 2022-09-21 with reprex v2.0.2