Stop `R` warnings from printing and capture them in a variable for later handling.

warnings.R

# Please run the code top to bottom and follow the comments.

# Task function with errors or warnings.
naughty_task <- function(error = TRUE, warning = FALSE) {
    # If warning.
    if (warning) {
        warning("Warning thrown.")
    }
        
    # If error.
    if (error) {
        stop("Error thrown.")
    }
}

# Test the function.
naughty_task(error = TRUE, warning = TRUE)

# Collect errors and warnings.
errors <- NULL
warnings <- NULL

# Try to run.
tryCatch(withCallingHandlers(
    # The expression to evaluate.
    expr = naughty_task(error = TRUE, warning = TRUE),

    # The warning handler.
    warning = function(w) {
        # Store warning.
        warnings <<- c(warnings, w$message)

        # Prevent the warning from being printed.
        invokeRestart("muffleWarning")
    }),

    # The error handler.
    error = function(e) {
        # Store error.
        errors <<- c(errors, e$message)
    }
)

# Check the collectors.
errors
warnings