Flickering line break

[boozook]

version: rustfmt 1.7.1-nightly (ba1d7f4a 2024-06-29) config: rustfmt.toml

Formatting is flickering for looooong chain like this:

from this

let removed = roots.extract_if(|root| {  /* long block */ }).count();

to this and back:

let removed = 
    roots.extract_if(|root| {  /* long block */ }).count();

Flickering in this case means following:

1. run rustfmt cargo/src/build/mod.rs => we've got new line-break
2. run rustfmt cargo/src/build/mod.rs => line-break is gone
3. repeat...

example as pr-annotation: https://github.com/boozook/playdate/pull/399#discussion_r1676418639

[ytmimi]

@boozook Thanks for the report. Please try to reduce this to a minimal reproducible example.

[boozook]

@ytmimi, I honestly tried to get an isolated minimal reproducible example, but I can't, sorry. I suppose there is something complex 🤷🏻‍♂️

Also, just as little addition I've made neat video-demo in the IDE

https://github.com/user-attachments/assets/4e58df5f-9df6-4fa0-850e-6f30882fbe60

[ytmimi]

Thanks for the video. You might try to copy the entire let removed assignment into a snippet that's just as indented as the current code and take it from there. If you're able to post that it might help someone start looking into what's going on.

[boozook]

@ytmimi, done! example.zip

Seems to it depends on length of ling lines inside the block.

Important things in the config:

hard_tabs = true
tab_spaces = 3

mod foo {
    fn foo() {
        artifacts.extract_if(|(art, roots)| {
                     let removed = roots.extract_if(|root| {
                                       let ct =
                                           determine_crate_types(cfg, art, target, tk.clone(), ck).collect::<Vec<_>>();
                                   })
                                   .inspect(|r| {
                                       log::trace!("    excluded: {p}::{t} {:?}", match r.node().unit().platform {
                                           CompileKind::Host => "host",
                                          CompileKind::Target(ref kind) => kind.short_name(),
                                       })
                                   })
                                   .count();
                 });
    }
}

Also there is one more problem - cases of match has various indent:

1. first has 5 tabs indent + 7*3 spaces align + 2 spaces in-block align
2. second - 4 tabs indent + 8*3 spaces align + 2 spaces in-block align