Merge pull request #62 from gadenbuie/appender-console-message

Add option to output to stdout or stderr in AppenderConsole

Author: s-fleck

R/Appender.R

@@ -139,6 +139,10 @@ Appender <- R6::R6Class(
 #' **crayon** installed log levels will be coloured by default
 #' (but you can modify this behaviour by passing a custom [Layout]).
 #'
+#' @param output Choose whether the message is printed to the \R console as
+#'   regular output (`"stdout"`, default in most cases) or as a message
+#'   (`"stderr"`, default inside a \pkg{knitr} rendering process).
+#'
 #' @family Appenders
 #' @seealso [LayoutFormat]
 #' @export
@@ -168,24 +172,43 @@ AppenderConsole <- R6::R6Class(
         timestamp_fmt = "%H:%M:%OS3",
         colors = getOption("lgr.colors", list())
       ),
-      filters = NULL
+      filters = NULL,
+      output = NULL
     ){
       self$set_threshold(threshold)
       self$set_layout(layout)
       self$set_filters(filters)
+      if (is.null(output)) {
+        output <- default_console_output(output)
+      }
+      private$output <- match.arg(output, c("stdout", "stderr"))
     },
 
     append = function(event){
-      cat(private$.layout$format_event(event), sep = "\n")
+      output <- switch(private$output, stdout = stdout(), stderr = stderr())
+      cat(private$.layout$format_event(event), sep = "\n", file = output)
     }
   ),
 
   active = list(
     destination = function() "console"
+  ),
+
+  private = list(
+    output = "stdout"
   )
 )
 
+default_console_output <- function(output) {
+  if (!is.null(output)) output
 
+  # In knitr, default to using stderr where log messages can be better handled
+  if (isTRUE(getOption("knitr.in.progress", FALSE))) {
+    return("stderr")
+  }
+
+  "stdout"
+}
 
 
 # AppenderFile ------------------------------------------------------------

man/AppenderConsole.Rd

@@ -202,6 +202,41 @@ test_that("AppenderConsole: $filter() works", {
 })
 
 
+test_that("AppenderConsole: $new(output = \"stderr\") works", {
+  app <- AppenderConsole$new(output = "stderr")
+
+  std_out <- textConnection("msg_out", open = "w", local = TRUE)
+  sink(std_out, append = TRUE, type = "message")
+  on.exit(sink(NULL, type = "message"), add = TRUE)
+
+  expect_silent(
+    app$append(event)
+  )
+
+  expect_match(
+    msg_out,
+    "ERROR.*:19:33.*foo.*bar"
+  )
+})
+
+test_that("AppenderConsole: chooses stderr by default when in knitr", {
+  opts <- options(knitr.in.progress = TRUE)
+  on.exit(options(opts), add = TRUE)
+
+  app <- AppenderConsole$new()
+  std_out <- textConnection("msg_out", open = "w", local = TRUE)
+  sink(std_out, append = TRUE, type = "message")
+  on.exit(sink(NULL, type = "message"), add = TRUE)
+
+  expect_silent(
+    app$append(event)
+  )
+
+  expect_match(
+    msg_out,
+    "ERROR.*:19:33.*foo.*bar"
+  )
+})
 
 
 # AppenderBuffer ----------------------------------------------------