Proof of concept: concurrent progress bars

[simonpcouch]

Related to #818. Largely vibe-coded and not intended to be merged--just a proof of concept.

A simple example in Positron:

pkgload::load_all()
options(cli.ansi = TRUE, cli.progress_show_after = 0)

fun <- function() {
  id1 <- cli_progress_bar("Downloads ", total = 20, current = FALSE, clear = FALSE)
  id2 <- cli_progress_bar("Processing", total = 20, current = FALSE, clear = FALSE)
  for (i in 1:20) {
    Sys.sleep(0.15)
    cli_progress_update(id = id1)
    Sys.sleep(0.15)
    cli_progress_update(id = id2)
  }
}
fun()

simple-concurrent-progress-bars.mov

[simonpcouch]

Noting that, via this entry point, this is only possible in Positron (and not RStudio).

[gaborcsardi]

Cool, so the R console in Positron now supports ANSI control sequences? All of them? How does one learn about this? How could we detect this?

[simonpcouch]

Okay, just did some exploration. Positron's R console uses a custom ANSI renderer.

It supports:

• Cursor movement: \033[A (up), \033[B (down), \033[C (forward), \033[D (backward), \033[H (absolute position)
• Line erasing: \033[K (to end), \033[2K (whole line)
• Display erasing: \033[J / \033[2J
• Carriage return: \r
• Full SGR: colors (16/256/truecolor), bold, italic, etc.
• Hyperlinks: OSC 8

These ones are not supported (silently consumed):

• \033[?25l / \033[?25h (hide/show cursor)
• Scroll regions, insert/delete line, save/restore cursor, alternate screen buffer

The needed biys were all present in the earliest commit to that file, in October 2023 (aeef2f28). This was before Sys.getenv("POSITRON") was introduced (July 2024), so anywhere Sys.getenv("POSITRON") == "1" is present should have those sequences.

[gaborcsardi]

so anywhere Sys.getenv("POSITRON") == "1" is present should have those sequences.

I am afraid that's probably not true, because env vars are inherited, so e.g. a job in the job pane will have POSITRON=1, or even just a plain subprocess will also have it.

[gaborcsardi]

This is probably unique to Positron, though:

> .Platform$GUI
[1] "Positron"

[gaborcsardi]

Can you write some summary about how this actually works? E.g. why do we need status_bar_lines (isn't that the length of status_bar?), what is status_bar_prev_content, etc?
Never mind, I understand it now.

We'll probably also need an opt-out mechanism, but we can do that later.

[gaborcsardi]

One thing I am not sure about is whether this should apply to status bars. (Which maybe nobody uses...) A status bar is just one line, even in a GUI.

[gaborcsardi]

@simonpcouch Thanks for the great PR!

[simonpcouch]

Awesome, thanks for sprucing this up! Excited to have this in.