nonstandard_macro_braces false positive

[DmitrySamoylov]

Lint name: nonstandard_macro_braces

I tried this code:

[package]
name = "nonstandard_macro_braces_issue"
version = "0.1.0"
edition = "2018"

[dependencies]
anyhow = "1.0.41"
fn-error-context = "0.1.2"

use fn_error_context::context;

fn main() {
    let _ = my_fn();
}

#[context("Some anyhow context")]
pub fn my_fn() -> anyhow::Result<()> {
    Ok(())
}

I expected to see no warnings

Instead, this happened (cargo +nightly clippy):

warning: use of irregular braces for `format!` macro
 --> src/main.rs:7:1
  |
7 | #[context("Some anyhow context")]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(clippy::nonstandard_macro_braces)]` on by default
help: consider writing `#(context("Some anyhow context"))`
 --> src/main.rs:7:1
  |
7 | #[context("Some anyhow context")]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#nonstandard_macro_braces
  = note: this warning originates in the attribute macro `context` (in Nightly builds, run with -Z macro-backtrace for more info)

context macro sources

Meta

• cargo clippy -V: clippy 0.1.53 (53cb7b0 2021-06-17)
• cargo +nightly clippy -V: clippy 0.1.55 (b3d11f9 2021-07-04)
• rustc -Vv:

  rustc 1.53.0 (53cb7b09b 2021-06-17)
  binary: rustc
  commit-hash: 53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b
  commit-date: 2021-06-17
  host: x86_64-unknown-linux-gnu
  release: 1.53.0
  LLVM version: 12.0.1
  

[Lymia]

This also seems to happen with my crate enumset. I have a very similar use of the write! macro that has caused a very similar warning: https://github.com/Lymia/enumset/blob/master/enumset_derive/src/lib.rs#L318

Issue I got: Lymia/enumset#25

[williballenthin]

And another data point:

warning: use of irregular braces for `vec!` macro
   --> pylancelot/src/lib.rs:283:1
    |
283 | #[pymethods]
    | ^^^^^^^^^^^^
    |
help: consider writing `#[pymethods]`
   --> pylancelot/src/lib.rs:283:1
    |
283 | #[pymethods]
    | ^^^^^^^^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#nonstandard_macro_braces
    = note: this warning originates in the attribute macro `pymethods` (in Nightly builds, run with -Z macro-backtrace for more info)

with the source:

#[pymethods]
impl Instruction {
    /// the length in bytes of the instruction.
    #[getter]
    pub fn length(&self) -> u8 {
        self.inner.length as u8
    }

[williballenthin]

I wonder if this was introduced with #7431. @DevinR528 does this look familiar?

[DevinR528]

I'm making the assumption that that commit (#7431) is not in a released version of clippy? There was this issue #7422 and then the PR to close it so hopefully, the problem is that the fix just hasn't gotten into a release.

It also shouldn't be warning without the lint being explicitly turned on because it was moved to nursery which also makes me think it's not there yet although cargo +nightly clippy -V: clippy 0.1.55 (b3d11f9 2021-07-04) worries me since that's the date the PR was merged 🤷 someone more familiar with the release process could answer these questions better @llogiq (I hope I didn't further screw this up).

[giraffate]

Although I don't know the details of that lint, we perform the sync between Clippy and rust-lang/rust every other week. So that fixes might not be applied in latest nightly yet.

[asomers]

This warning is firing for Mockall, too. It looks like every project that uses Mockall will trigger the warning, and Clippy's suggested replacement code doesn't even compile.

[EliasHolzmann]

Also seems to happen for Rocket attributes like get.

[shepmaster]

This likely happens for any procedural macro that uses one of the macros checked by this lint. This jives with what is described in #7431

For example, in SNAFU, the procedural macro does:

let match_arm = quote! {
    #pattern_ident { #field_names } => {
        write!(#FORMATTER_ARG, #format)
    }
};

This generates code like

Error :: Leaf { ref user_id } =>
           { write! (__snafu_display_formatter, stringify! (Leaf)) }

Note the spaces between write! and (.

[asomers]

It seems this issue was fixed, probably by #7431 . Can it be closed?

[giraffate]

Yes, so I'm closing this.

Thanks for the reports!