manual_map thinks rust has non-local control flow in closures

[jyn514]

Lint name: manual_map

I tried this code:

        let github_repo = match self.github_stats {
            Some(stats) => Some(stats.create(&mut self.db.conn())?),
            None => None,
        };

I expected to see this happen: No warning, because this is non-trivial to replicate with combinators.

Instead, this happened: Clippy warned that this can use map:

warning: manual implementation of `Option::map`
   --> src/test/fakes.rs:319:27
    |
319 |           let github_repo = match self.github_stats {
    |  ___________________________^
320 | |             Some(stats) => Some(stats.create(&mut self.db.conn())?),
321 | |             None => None,
322 | |         };
    | |_________^ help: try this: `self.github_stats.map(|stats| stats.create(&mut self.db.conn())?)`
    |
    = note: `#[warn(clippy::manual_map)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_map

and then fails to apply its own suggestion:

The following errors were reported:
error[E0277]: the `?` operator can only be used in a closure that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
   --> src/test/fakes.rs:319:57
    |
319 |         let github_repo = self.github_stats.map(|stats| stats.create(&mut self.db.conn())?);
    |                                                 --------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |                                                 |       |
    |                                                 |       cannot use the `?` operator in a closure that returns `std::string::String`
    |                                                 this function should return `Result` or `Option` to accept `?`
    |
    = help: the trait `std::ops::Try` is not implemented for `std::string::String`
    = note: required by `std::ops::Try::from_error`

error: aborting due to previous error

Meta

• cargo clippy -V: clippy 0.1.52 (45b3c28 2021-03-04)
• rustc -Vv:

rustc 1.52.0-nightly (45b3c2851 2021-03-04)
binary: rustc
commit-hash: 45b3c28518e4c45dfd12bc2c4400c0d0e9639927
commit-date: 2021-03-04
host: x86_64-unknown-linux-gnu
release: 1.52.0-nightly
LLVM version: 12.0.0

[llogiq]

I think the problem may be that it only looks at the parent item's return type instead of the closure's one.

[Y-Nak]

I think this was fixed in #6801.

#![warn(clippy::manual_map)]

struct Foo {
    x: i32,
}

impl Foo {
    fn add(&self, arg: i32) -> Result<i32, String> {
        Ok(self.x + arg)
    }
}

fn f() -> Result<i32, String> {
    let obj = Foo { x: 1 };

    match Some(0) {
        Some(x) => Some(obj.add(x)?),
        None => None,
    };

    Ok(1)
}

fn main() {}

doesn't trigger the lint in the current version, while it triggers the lint in the version right before #6801 was merged.

[jyn514]

Yup, works great on the latest nightly, thanks!