Add labels to the default progress bar and allow users to provide a custom progress bar

NEWS.md

@@ -1,5 +1,11 @@
 # CHANGES IN knitr VERSION 1.42
 
+## NEW FEATURES
+
+- Users can specify a custom progress bar for `knit()` now. The default is still a text progress bar created from `utils::txtProgressBar()`. To specify a custom progress bar, set `options(knitr.progress.fun = function(total, labels) {})`. This function should take arguments `total` (the total number of chunks) and `labels` (the vector of chunk labels), create a progress bar, and return a list of two methods: `list(update = function(i) {}, done = function() {})`. The `update()` method takes `i` (index of the current chunk) as the input and updates the progress bar. The `done()` method closes the progress bar. See https://yihui.org/knitr/options/#global-r-options for documentation and examples.
+
+- The default text progress bar is still written to `stdout()` by default, but can also be written to other connections or `stderr()` now. To do so, set `options(knitr.progress.output = )` to a connection or `stderr()`.
+
 ## MAJOR CHANGES
 
 - `knit()` no longer prints out chunk options beneath the text progress bar while knitting a document (thanks, @hadley, #1880).

R/output.R

@@ -289,8 +289,9 @@ process_file = function(text, output) {
     labels = unlist(lapply(groups, function(g) {
       if (is.list(g$params)) g[[c('params', 'label')]] else ''
     }))
-    pb = txtProgressBar(0, n, char = '.', style = 3)
-    on.exit(close(pb), add = TRUE)
+    pb_fun = getOption('knitr.progress.fun', txt_pb)
+    pb = if (is.function(pb_fun)) pb_fun(n, labels)
+    on.exit(if (!is.null(pb)) pb$done(), add = TRUE)
   }
   wd = getwd()
   for (i in 1:n) {
@@ -302,7 +303,7 @@ process_file = function(text, output) {
       }
       break  # must have called knit_exit(), so exit early
     }
-    if (progress) setTxtProgressBar(pb, i)
+    if (progress && !is.null(pb)) pb$update(i)
     group = groups[[i]]
     res[i] = withCallingHandlers(
       if (tangle) process_tangle(group) else process_group(group),

R/parser.R

@@ -333,7 +333,6 @@ get_option_comment = function(engine) {
 
 print.block = function(x, ...) {
   params = x$params
-  cat(' chunk:', params$label, '\n')
   if (opts_knit$get('verbose')) {
     code = knit_code$get(params$label)
     if (length(code) && !is_blank(code)) {

R/utils.R

@@ -1085,3 +1085,30 @@ str_split = function(x, split, ...) {
   y[x == ''] = list('')
   y
 }
+
+# default progress bar function in knitr: create a text progress bar, and return
+# methods to update/close it
+txt_pb = function(total, labels) {
+  s = ifelse(labels == '', '', sprintf(' (%s)', labels))  # chunk labels in ()
+  w = nchar(s)  # widths of labels
+  n = max(w)
+  # right-pad spaces for same width of all labels so a wider label of the
+  # progress bar in a previous step could be completely wiped (by spaces)
+  s = paste0(s, strrep(' ', n - w))
+  w2 = getOption('width')
+  con = getOption('knitr.progress.output', '')
+  pb = txtProgressBar(
+    0, total, 0, '.', width = max(w2 - 10 - n, 10), style = 3, file = con
+  )
+  list(
+    update = function(i) {
+      setTxtProgressBar(pb, i)
+      cat(s[i], file = con)  # append chunk label to the progress bar
+    },
+    done = function() {
+      # wipe the progress bar
+      cat(paste0('\r', strrep(' ', max(w2, 10) + 10 + n)), file = con)
+      close(pb)
+    }
+  )
+}