Clippy lints / Suspicious
Clippy lint · Suspicious · checked with Clippy 0.1.99
clippy::block_scrutinee: Warns when a match, if let, or while let scrutinee is wrapped in a block. This lint only triggers on the 2021 edition and older
What it meansWarns when a match, if let, or while let scrutinee is wrapped in a block. This lint only triggers on the 2021 edition and older. It is in the suspicious group and warns by default.
Does it matter?
It is unusual to write { expr } when you could just have written expr, and it is unlikely that anyone would write that for any reason other than wanting temporaries in expr to be dropped before executing the body of the match/if let/while statement. However, prior to the 2024 edition, wrapping the scrutinee in a block did not drop temporaries before the body executes.
Code that is most likely wrong or useless. Warns by default.
How to fix it
Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:
Flagged
if let Some(x) = { my_function() } { .. }
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::block_scrutinee)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
block_scrutinee = "allow"One run
cargo clippy -- -A clippy::block-scrutineeThe [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.
Clippy's own documentation
What it does
Warns when a match, if let, or while let scrutinee is wrapped in a block. This lint only triggers on the 2021 edition and older.
Why is this bad?
It is unusual to write { expr } when you could just have written
expr, and it is unlikely that anyone would write that for any reason
other than wanting temporaries in expr to be dropped before executing
the body of the match/if let/while statement. However, prior to
the 2024 edition, wrapping the scrutinee in a block did not drop
temporaries before the body executes.
Example
if let Some(x) = { my_function() } { .. }
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
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- by_ref_peekable_peekcalling `.by_ref().peekable().peek()` will advance the underlying iterator and consume its first output
- cast_abs_to_unsignedcasting the result of `i32::abs()` to u32
- cast_enum_constructorcast of an enum tuple constructor to an integer
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
Up next
Related lintclippy::await_holding_lockChecks for calls to await while holding a non-async-aware MutexGuardRead it next →Did this answer your question?