cargo clippy --fix generated broken code

[rbtcollins]

Output from clippy.

after fixes were automatically applied the compiler reported errors within these files:

  * examples/threads.rs

This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see 
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag

The following errors were reported:
error[E0277]: the `?` operator can only be used in an async block that returns `Result` or `Option` (or another type that implements `std::ops::FromResidual`)
  --> examples/threads.rs:61:32
   |
60 |       rt.block_on(async {
   |  _______________________-
61 | |         client.register().await?
   | |                                ^ cannot use the `?` operator in an async block that returns `()`
62 | |     })?;
   | |_____- this function should return `Result` or `Option` to accept `?`
   |
   = help: the trait `std::ops::FromResidual<std::result::Result<std::convert::Infallible, std::boxed::Box<dyn std::error::Error + std::marker::Send + std::marker::Sync>>>` is not implemented for `()`

error[E0277]: the `?` operator can only be applied to values that implement `std::ops::Try`
  --> examples/threads.rs:60:5
   |
60 | /     rt.block_on(async {
61 | |         client.register().await?
62 | |     })?;
   | |_______^ the `?` operator cannot be applied to type `()`
   |
   = help: the trait `std::ops::Try` is not implemented for `()`

error: aborting due to 2 previous errors

I would be happy if either the lint didn't fire, or if clippy fixed things with code that works.

Meta

The same error occurs with nightly.

rustc --version --verbose:

rustc 1.64.0 (a55dd71d5 2022-09-19)
rustc 1.66.0-nightly (57f097ea2 2022-10-01)

[Alexendoo]

Could you share the output of running cargo clippy without --fix, or the code this occurred on?

[rbtcollins]

https://github.com/rbtcollins/unleash-client-rust/blob/744b0e64d879b7c681fe14f922bbcf943d8efdf5/examples/threads.rs#L61-L68

[rbtcollins]

The allow was added after this.

    rt.block_on(async {
        if let Err(e) = client.register().await {
            Err(e)
        } else {
            Ok(())
        }
    })?;

for permanence

[BenjaminBrienen]

I also get this.

warning: failed to automatically apply fixes suggested by rustc to crate `wgsl_analyzer`

after fixes were automatically applied the compiler reported errors within these files:

  * crates/wgsl-analyzer/src/lsp/capabilities.rs

This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust-clippy/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag

The following errors were reported:
error[E0277]: the `?` operator can only be used in a method that returns `Result` or `Option` (or another type that implements `std::ops::FromResidual`)
   --> crates/wgsl-analyzer/src/lsp/capabilities.rs:142:34
    |
138 |     fn code_action_capabilities(&self) -> CodeActionProviderCapability {
    |     ------------------------------------------------------------------ this function should return `Result` or `Option` to accept `?`
...
142 |                         .as_ref()?;
    |                                  ^ cannot use the `?` operator in a method that returns `lsp_types::CodeActionProviderCapability`

error[E0277]: the `?` operator can only be used in a method that returns `Result` or `Option` (or another type that implements `std::ops::FromResidual`)
   --> crates/wgsl-analyzer/src/lsp/capabilities.rs:459:34
    |
455 |     pub fn inlay_hint_resolve_support_properties(&self) -> FxHashSet<&str> {
    |     ---------------------------------------------------------------------- this function should return `Result` or `Option` to accept `?`
...
459 |                         .as_ref()?;
    |                                  ^ cannot use the `?` operator in a method that returns `std::collections::HashSet<&str, rustc_hash::FxBuildHasher>`

error[E0277]: the `?` operator can only be used in a method that returns `Result` or `Option` (or another type that implements `std::ops::FromResidual`)
   --> crates/wgsl-analyzer/src/lsp/capabilities.rs:474:34
    |
470 |     pub fn completion_resolve_support_properties(&self) -> FxHashSet<&str> {
    |     ---------------------------------------------------------------------- this function should return `Result` or `Option` to accept `?`
...
474 |                         .as_ref()?;
    |                                  ^ cannot use the `?` operator in a method that returns `std::collections::HashSet<&str, rustc_hash::FxBuildHasher>`

error: aborting due to 3 previous errors

[blyxyas]

This issue is currently not happening anymore in the repo's current state. Could you post an example of the problematic code @BenjaminBrienen? =^w^=

[BenjaminBrienen]

This code would cause it if you remove the closure wrapper

https://github.com/rust-lang/rust/blob/8de4c7234dd9b97c9d76b58671343fdbbc9a433e/src/tools/rust-analyzer/crates/rust-analyzer/src/lsp/capabilities.rs#L211

[blyxyas]

Minimized example of this behaviour:

fn a() -> bool {
    (|| {
        Some(true)
    })() == Some(true)
}

Which rustfix tries to change into:

fn a() -> bool {
    {
        Some(true)
    } == Some(true)
}

which produces:

error: expected expression, found `==`
 --> src/lib.rs:4:7
  |
4 |     } == Some(true)
  |       ^^ expected expression

error[E0308]: mismatched types
 --> src/lib.rs:3:9
  |
3 |         Some(true)
  |         ^^^^^^^^^^ expected `()`, found `Option<bool>`
  |
  = note: expected unit type `()`
                  found enum `std::option::Option<bool>`

[odysa]

@rustbot claim

[odysa]

I think the expected behavior is

(|| { Some(true) })() == Some(true)
// suggested as
Some(true) == Some(true)

[odysa]

Possible solution:
If the closure body is a block, and the block contains no statements but has a final expression, we can suggest replacing the entire closure with just that expression.
For example, (|| { Some(true) })() can be simplified to Some(true).

if let ExprKind::Block(block, _) = body.kind
     && block.stmts.is_empty()
     && let Some(expr) = block.expr {
		// suggest inner expr
}