Printed hint for lint `or_fun_call` is cropped and does not show the solution

[aleksanderkrauze]

Description

Desctiption

Following code snippet was correctly marked by clippy as or_fun_call. However it's output could be better. Problem here is at the last line of this block, but clippy's hint is cropped and this bottom part is not shown. It seams that clippy is omitting different lines in the warning and in the hint.

Code

self.frames
    .iter()
    .map(|f| f.encode())
    .reduce(|mut acc, mut f| {
        acc.append(&mut f);
        acc
    })
    .unwrap_or(Vec::new())

Clippy's output

warning: use of `unwrap_or` followed by a call to `new`
  --> src/server/frame.rs:89:9
   |
89 | /         self.frames
90 | |             .iter()
91 | |             .map(|f| f.encode())
92 | |             .reduce(|mut acc, mut f| {
...  |
95 | |             })
96 | |             .unwrap_or(Vec::new())
   | |__________________________________^
   |
   = note: `#[warn(clippy::or_fun_call)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#or_fun_call
help: try this
   |
89 ~         self.frames
90 +             .iter()
91 +             .map(|f| f.encode())
92 +             .reduce(|mut acc, mut f| {
93 +                 acc.append(&mut f);
94 +                 acc
 ...

Version

rustc 1.57.0 (f1edd0429 2021-11-29)
binary: rustc
commit-hash: f1edd0429582dd29cccacaf50fd134b05593bd9c
commit-date: 2021-11-29
host: x86_64-unknown-linux-gnu
release: 1.57.0
LLVM version: 13.0.0

Additional Labels

@rustbot label +C-enhancement

[marekdownar]

Isn't it strictly connected with current rustc diagnostics emitter?
pub const MAX_SUGGESTION_HIGHLIGHT_LINES: usize = 6;
It looks like DiagnosticBuilder span_suggestion formats the result suggestion with max 6 lines of output.

[xFrednet]

This is strictly connected. However, we can adjust the help message to say try using `unwrap_or_else(Vec::new)`: to make the suggestion clear if the snippet spans over multiple lines. Or we could restrict the suggestion span to the .unwrap_or(Vec::new()) call, as the previous text stays the same. Both would be valid solutions 🙃