2024 edition migration of ref in patterns suboptimal: fixed up by clippy --fix

The 2024 edition migration changed this:

impl TryFrom<&Selector> for konfigkoll_utils::line_edit::Selector {
    type Error = eyre::Error;

    fn try_from(value: &Selector) -> Result<Self, Self::Error> {
        match value {
            Selector::All => Ok(Self::All),
            Selector::Eof => Ok(Self::Eof),
            Selector::Line(n) => Ok(Self::Line(*n)),
            Selector::Range(a, b) => Ok(Self::Range(*a, *b)),
            Selector::Regex(r) => Ok(Self::Regex(Regex::new(r).wrap_err("invalid regex")?)),
            Selector::Function(ref f) => {
                let f = f.clone();
                Ok(Self::Function(Rc::new(move |lineno, s| {
                    let guard = f.borrow_mut().expect("Failed to borrow function object");
                    match guard.call::<_, bool>((lineno, s)) {
                        VmResult::Ok(v) => v,
                        VmResult::Err(e) => {
                            tracing::error!(
                                "Error in custom selector function {:?}: {:?}",
                                *guard,
                                e
                            );
                            false
                        }
                    }
                })))
            }
        }
    }
}

into this:

impl TryFrom<&Selector> for konfigkoll_utils::line_edit::Selector {
    type Error = eyre::Error;

    fn try_from(value: &Selector) -> Result<Self, Self::Error> {
        match value {
            Selector::All => Ok(Self::All),
            Selector::Eof => Ok(Self::Eof),
            Selector::Line(n) => Ok(Self::Line(*n)),
            Selector::Range(a, b) => Ok(Self::Range(*a, *b)),
            Selector::Regex(r) => Ok(Self::Regex(Regex::new(r).wrap_err("invalid regex")?)),
            &Selector::Function(ref f) => {
                let f = f.clone();
                Ok(Self::Function(Rc::new(move |lineno, s| {
                    let guard = f.borrow_mut().expect("Failed to borrow function object");
                    match guard.call::<_, bool>((lineno, s)) {
                        VmResult::Ok(v) => v,
                        VmResult::Err(e) => {
                            tracing::error!(
                                "Error in custom selector function {:?}: {:?}",
                                *guard,
                                e
                            );
                            false
                        }
                    }
                })))
            }
        }
    }
}

Then running cargo +beta clippy --fix changed it ~~right back~~ to Selector::Function(f).

When runing without --fix this is the clippy message:

warning: dereferencing a tuple pattern where every element takes a reference
   --> crates/konfigkoll_script/src/plugins/patch.rs:105:13
    |
105 |             &Selector::Function(ref f) => {
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrowed_reference
    = note: `#[warn(clippy::needless_borrowed_reference)]` on by default
help: try removing the `&` and `ref` parts
    |
105 -             &Selector::Function(ref f) => {
105 +             Selector::Function(f) => {
    |

warning: dereferencing a tuple pattern where every element takes a reference
   --> crates/konfigkoll_script/src/plugins/patch.rs:208:13
    |
208 |             &Action::Function(ref f) => {
    |             ^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrowed_reference
help: try removing the `&` and `ref` parts
    |
208 -             &Action::Function(ref f) => {
208 +             Action::Function(f) => {
    |

I expected to see this happen: ~~A coherrent decision on what way is the proper way to write this. Rustc and clippy shouldn't fight each other.~~ The edition migration shouldn't be sloppy and need to be fixed up by clippy.

Instead, this happened: Clippy has to clean up after rustc.

I have also pushed this to a branch in my repo, in case you need more context for investigating this: https://github.com/VorpalBlade/paketkoll/tree/feature/edition-2024 (the migration and the reversion are each in a separate commit). There seemed to be a few more instances of the same needless_borrowed_reference in other files too, but I think they are the same underlying cause.

Meta

rustc --version --verbose:

$ rustc +beta --version --verbose                   
rustc 1.85.0-beta.5 (441650704 2025-01-20)
binary: rustc
commit-hash: 44165070434aab38db1115448621880a35da00ff
commit-date: 2025-01-20
host: x86_64-unknown-linux-gnu
release: 1.85.0-beta.5
LLVM version: 19.1.7

Backtrace

Not relevant? Didn't crash after all...

@rustbot

@rustbot modify labels: A-edition-2024

That's surprising indeed, the lint shouldn't trigger on that. What the type of the payload of the Function variant?

The type here is:

#[derive(Clone)]
#[non_exhaustive]
pub enum Selector {
    /// Match all lines
    All,
    /// End of file (useful to insert lines at the very end)
    Eof,
    /// Match a specific line number (1-indexed)
    Line(usize),
    /// A range of line numbers (1-indexed, inclusive)
    Range(usize, usize),
    /// A regex to match the line
    Regex(Regex),
    /// A custom function, passed the line number and current line
    #[allow(clippy::type_complexity)]
    Function(Rc<dyn Fn(usize, &str) -> bool>),
}

However, this also happens separately with the function variant of this other enum as well:

#[derive(Debug, Any)]
#[rune(item = ::patch)]
enum Action {
    /// Copy the current line to the output. Only needed when auto-print is
    /// disabled.
    #[rune(constructor)]
    Print,
    /// Delete the current line and short circuit the rest of the program
    /// (immediately go to the next line)
    #[rune(constructor)]
    Delete,

    // ... [cut out for brevity, there are many more variants] ...

    #[rune(constructor)]
    RegexReplace(#[rune(get)] String, #[rune(get)] String),
    /// Like `RegexReplace` but replaces all matches on the line.
    #[rune(constructor)]
    RegexReplaceAll(#[rune(get)] String, #[rune(get)] String),
    /// A sub-program that is executed. Will share pattern space with parent
    /// program
    Subprogram(LineEditor),
    /// A custom function passed the current pattern buffer, returning a new
    /// pattern buffer
    #[rune(constructor)]
    Function(#[rune(get)] Shared<rune::runtime::Function>),
}

As well as this change in save.rs (that clippy also undoes):

--- a/crates/konfigkoll_core/src/save.rs
+++ b/crates/konfigkoll_core/src/save.rs
@@ -28,13 +28,13 @@ pub fn save_fs_changes<'instruction>(
     for instruction in instructions {
         let comment = match (instruction.pkg, &instruction.comment) {
             (None, None) => CompactString::default(),
-            (None, Some(ref comment)) => {
+            (None, &Some(ref comment)) => {
                 format_compact!(" // {comment}")
             }
             (Some(pkg), None) => {
                 format_compact!(" // [{}]", pkg.as_str(interner))
             }
-            (Some(pkg), Some(ref comment)) => {
+            (Some(pkg), &Some(ref comment)) => {
                 format_compact!(" // [{}] {comment}", pkg.as_str(interner))
             }
         };

Where comment is a &CompactString according to the Rust Analyzer inlay hint. So the matched type is (Option<PackageRef>, &Option<CompactString>). Where PackageRef is a newtype around lasso::Spur and CompactString is from the compact_str crate.

And in the third case (state.rs) I have this type, and the second member of the Apply variant is affected (the Arc is not).

pub enum DiffGoal<'map, 'files> {
    Apply(Arc<dyn Files>, &'map PathMap<'files>),
    Save,
}

I would suggest you take a look at the whole diff of VorpalBlade/paketkoll@7ec3d44 to see what clippy changed back as there are several instances of this, with different types. I don't know which ones should be considered separate bugs and which ones should be the same. They all look related to me.

I see two issues at play here:

The migration lint is a bit stupid and doesn't suggest the optimal pattern. It should really be suggesting Some(ref comment) => Some(comment) instead of => &Some(ref comment).
It seems you've found a case where the migration lint triggers when it really shouldn't. Are you quite sure the initial code wasn't Selector::Function(ref f)? If it was ref f then the lint is working as intended (if stupid).

Ah, yes it seems you are right looking at VorpalBlade/paketkoll@a715c59. There was an extra ref there. So your point 2 is indeed not an issue.

Point 1 remains. Clippy shouldn't have to clean up from the migration being sloppy.

When I'm not on mobile I will edit the title and the original post to clarify that clippy didn't actually revert, just clean up.

@dianne

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2024 edition migration of `ref` in patterns suboptimal: fixed up by clippy --fix #136047

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2024 edition migration of ref in patterns suboptimal: fixed up by clippy --fix #136047

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VorpalBlade commented on Jan 25, 2025

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2024 edition migration of `ref` in patterns suboptimal: fixed up by clippy --fix #136047