rust-lang / rust-lang/rustfmt

Gives up on chains if any line is too long.

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#3,863 60 comments 186 reactions 0 assignees View on GitHub

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A-call-chains A-strings C-bug I-poor-formatting
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Rust
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Description

If there is a method call chain, and just one call exceeds max_width, it seems like rustfmt gives up and doesn't format anything.

Example:

fn f() {
    foo("This text is under the max_width limit, and shouldn't cause any problems on its own.").long("But this line is extra long, and doesn't fit within 100 max_width. 1234567890123456789").baz().collect().unwrap();
}

No format changes will be applied to this. I'm also a bit surprised that error_on_line_overflow does not complain.

I would expect it to wrap each call chain element, even if one of them is too long, such as:

fn f() {
    foo("This text is under the max_width limit, and shouldn't cause any problems on its own.")
        .long("But this line is extra long, and doesn't fit within 100 max_width. 1234567890123456789")
        .baz()
        .collect()
        .unwrap();
}

All default settings.
rustfmt 1.4.8-nightly (afb1ee1c 2019-09-08)

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the issue's method-chain example with the default max_width and error_on_line_overflow settings, then trace rustfmt's method-chain formatting behavior. Done means each chain element is wrapped as shown, including when one call exceeds max_width, and the relevant overflow behavior is covered by a regression test.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
tooling
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
48/100

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