Strange behavior with multi-line prompts

[NfNitLoop]

Describe the bug

From a conversation in Discord:

Is this a bug, or me not understanding something about the way prompts work?
let-env PROMPT_INDICATOR = {|| "> " } is the default. But if I change it to:
let-env PROMPT_INDICATOR = {|| "\n> " }
I do get the newline, but the > disappears?
But if I prefix with a space like this, then I get both:
let-env PROMPT_INDICATOR = {|| " \n> " }

How to reproduce

1. let-env PROMPT_INDICATOR = {|| "\n> " }

Notice that you get a prompt w/ a newline, but no >.

Expected behavior

I expected to have a prompt of "> " on a line by itself. (I prefer my prompts always start at the same indentation, regardless of how deep I am into a random file path.)

Or, if there's some additional behavior going on for the various prompts (ex: if some trimming is going on, or multi-line prompts aren't supported), I'd expect to see that in docs. 😊

Screenshots

Configuration

key	value
version	0.78.0
branch
commit_hash
build_os	macos-aarch64
build_target	aarch64-apple-darwin
rust_version	rustc 1.68.2 (9eb3afe9e 2023-03-27) (built from a source tarball)
cargo_version	cargo 1.68.1 (6feb7c9cf 2023-03-26)
build_time	2023-04-04 18:47:00 +00:00
build_rust_channel	release
features	default, zip
installed_plugins

Additional context

No response

[Mehrbod2002]

@sholderbach Can I work on it ?

[amtoine]

@sholderbach Can I work on it ?

anyone is welcome to contribute, i'm sure @sholderbach would say "please do so" 😉

[NfNitLoop]

Oh! I forgot to mention that I'd already tried moving the newline into create_left_prompt by changing its last line to this:

$path_segment + "\n"

… but that newline seemed to get lost (trimmed?). It might be worth checking if whatever is going on with PROMPT_INDICATOR is also happening with the other PROMPT_ variables.

[hyrious]

It seems each PROMPT_* variables' last newline character is dropped:

nushell/crates/nu-cli/src/prompt_update.rs

Lines 80 to 89 in a5087c4

	output.map(|mut x| {
	// Just remove the very last newline.
	if x.ends_with('\n') {
	x.pop();
	}
	if x.ends_with('\r') {
	x.pop();
	}
	x

[maxomatic458]

seems to be the same problem described in nushell/reedline#707

i think this can just be reproduced in reedline, so the issue is probably there somewhere