"left behind trailing whitespace" on contents of skipped item

[kpreid]

I ran cargo fmt and it reported error[internal]: left behind trailing whitespace and failed to format a file. Minimal reproduction:

impl Foo {
    #[rustfmt::skip]
    fn foo() {
        Bar      
        //     ^ there is whitespace here
    }
}

error[internal]: left behind trailing whitespace
 --> /playground/src/main.rs:4:4:11
  |
4 |         Bar      
  |            ^^^^^^
  |

warning: rustfmt has failed to format. See previous 1 errors.

The original case was a const array of enum variants, so this is not specific to fns.

If the #[rustfmt::skip] attribute is relocated to the entire impl block then the code is (correctly) skipped silently.

Meta

This seems very similar to #2037, but that specific case has not regressed.

• rustfmt version: 1.4.25-stable (0f29ff6 2020-11-11) or 1.4.36-nightly (2021-02-07 7de6968)
• From where did you install rustfmt?: rustup or Rust Playground
• How do you run rustfmt: cargo fmt or Rust Playground

[calebcartwright]

Thanks for reaching out! Though we're obviously dealing with items here, the same nested issue discussed on #2037 for expressions is almost certainly at play here as well since we have nested items.

While the first fn item is being skipped, any other nested items, as well as the top level impl item itself will still be formatted, e.g. your snippet sans trailing spaces with an additional item:

impl      Foo          {
    #[rustfmt::skip]
    fn foo() {
        Bar
        //     ^ there is whitespace here
    }
    
    
fn bar() { Qux // asdf
}
}

At a certain point, I'm not sure how feasible/worthwhile it will be to have rustfmt try to work around all these user-configured scenarios. If rustfmt is giving you a hard error, then I'd assume you have error_on_unformatted enabled, otherwise rustfmt would just emit a warning but still format the file. This would mean that you're explicitly telling rustfmt to ignore a nested item that contains trailing whitespace, and at the same time telling rustfmt to fail loudly in trailing whitespace cases.

Sure you're already aware of this, but some readily available options would be to remove the trailing whitespace manually or disable the error_on_unformatted behavior (which is off by default).

I'll update the labels on this and keep it open in case someone's interested in working on it, though tbh it's a relatively low priority. Thanks again for the report!

[kpreid]

If rustfmt is giving you a hard error, then I'd assume you have error_on_unformatted enabled

I don't (it's not mentioned in my rustfmt.toml), but the symptom I actually noticed was that VS Code + rust-analyzer was (silently) failing to format on save. Testing further, it seems that cargo fmt gives a warning and formats the rest of the file, but whatever rust-analyzer is doing aborts (and doesn't show me the error).

From looking at the source code of rust-analyzer it looks like rust-analyzer is calling rustfmt on a copy of the file (reasonable, since the “real” file might be getting formatted but not saved), then ignoring the formatted copy when rustfmt exits with status 1, on the assumption that there was a syntax error (wrong in this case).

So it sounds like this is arguably a bug in rust-analyzer — though it might be convenient for them if there was a exit code for "I formatted but there were errors" separate from "there were errors such that I could not format".

[timblakely]

Just ran into this too; was wondering why my formatting suddenly stopped. I don't have a rustfmt.toml, so I would assume that the setting would have defaulted to false...? Worked around by setting the vscode setting "Trim trailing whitespace on save", but +1 on the potential unique return code that @kpreid suggested.