clippy::range_plus_one: Checks for exclusive ranges where 1 is added to the upper bound, e.g., x..(y+1)

for i in x..(y+1) {
    // ..
}

for i in x..=y {
    // ..
}

[lints.clippy]
range_plus_one = "warn"

#![warn(clippy::range_plus_one)]

cargo clippy -- -W clippy::range-plus-one

Clippy's own documentation

What it does

Checks for exclusive ranges where 1 is added to the upper bound, e.g., x..(y+1).

Why is this bad?

The code is more readable with an inclusive range like x..=y.

Limitations

The lint is conservative and will trigger only when switching from an exclusive to an inclusive range is provably safe from a typing point of view. This corresponds to situations where the range is used as an iterator, or for indexing.

Known problems

Will add unnecessary pair of parentheses when the expression is not wrapped in a pair but starts with an opening parenthesis and ends with a closing one. I.e., let _ = (f()+1)..(f()+1) results in let _ = ((f()+1)..=f()).

Also in many cases, inclusive ranges are still slower to run than exclusive ranges, because they essentially add an extra branch that LLVM may fail to hoist out of the loop.

Example

for i in x..(y+1) {
    // ..
}

Use instead:

for i in x..=y {
    // ..
}

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

Related lints

• too_many_linesChecks for functions with a large amount of lines
• missing_errors_docChecks the doc comments of publicly visible functions that return a Result type and warns if there is no # Errors section
• must_use_candidateChecks for public functions that have no #[must_use] attribute, but return something not already marked must-use, have no mutable arg and mutate no statics
• ptr_offset_by_literaluse of `offset` with a literal
• pub_underscore_fieldsChecks whether any field of the struct is prefixed with an _ (underscore) and also marked pub (public)
• range_minus_oneChecks for inclusive ranges where 1 is subtracted from the upper bound, e.g., x..=(y-1)
• redundant_closure_for_method_callsredundant closure
• redundant_elseredundant else block
• ref_as_ptrreference as raw pointer

All 847 Clippy lints · Rust compiler errors · Cargo.toml checker