Clippy lint · Pedantic · checked with Clippy 0.1.99

clippy::unnecessary_literal_bound: Detects functions that are written to return &str that could return &'static str but instead return a &'a str

What it meansDetects functions that are written to return &str that could return &'static str but instead return a &'a str. It is in the pedantic group and off by default.

Does it matter?

This leaves the caller unable to use the &str as &'static str, causing unnecessary allocations or confusion. This is also most likely what you meant to write.

Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.

How to fix it

Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.

Flagged

impl MyType {
    fn returns_literal(&self) -> &str {
        "Literal"
    }
}

Write this instead

impl MyType {
    fn returns_literal(&self) -> &'static str {
        "Literal"
    }
}

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
unnecessary_literal_bound = "warn"

In code

#![warn(clippy::unnecessary_literal_bound)]

One run

cargo clippy -- -W clippy::unnecessary-literal-bound

The [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.

Pedanticgroup

allowdefault level

yesfixed by cargo clippy --fix

1.84.0added in Rust

Clippy's own documentation

What it does

Detects functions that are written to return &str that could return &'static str but instead return a &'a str.

Why is this bad?

This leaves the caller unable to use the &str as &'static str, causing unnecessary allocations or confusion. This is also most likely what you meant to write.

Example

impl MyType {
    fn returns_literal(&self) -> &str {
        "Literal"
    }
}

Use instead:

impl MyType {
    fn returns_literal(&self) -> &'static str {
        "Literal"
    }
}

Or, in case you may return a non-literal str in future:

impl MyType {
    fn returns_literal<'a>(&'a self) -> &'a str {
        "Literal"
    }
}

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

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