Clippy lints / Restriction
Clippy lint · Restriction · checked with Clippy 0.1.99
clippy::string_slice: indexing into a string may panic if the index is within a UTF-8 character
What it meansChecks for slice operations on strings It is in the restriction group and off by default.
What you see
warning: indexing into a string may panic if the index is within a UTF-8 character --> main.rs:3:2 | 3 | &"Ölkanne"[1..]; | ^^^^^^^^^^^^^^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#string_slice = note: requested on the command line with `-W clippy::string-slice`
Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.
Does it matter?
UTF-8 characters span multiple bytes, and it is easy to inadvertently confuse character counts and string indices. This may lead to panics, and should warrant some test cases containing wide UTF-8 characters. This lint is most useful in code that should avoid panics at all costs.
Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.
How to fix it
Clippy does not fix this one automatically. Change the code by hand:
Flagged
&"Ölkanne"[1..];
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]
string_slice = "warn"In code
#![warn(clippy::string_slice)]One run
cargo clippy -- -W clippy::string-sliceThe [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
Checks for slice operations on strings
Why restrict this?
UTF-8 characters span multiple bytes, and it is easy to inadvertently confuse character counts and string indices. This may lead to panics, and should warrant some test cases containing wide UTF-8 characters. This lint is most useful in code that should avoid panics at all costs.
Known problems
Probably lots of false positives. If an index comes from a known valid position (e.g.
obtained via char_indices over the same string), it is totally OK.
Example
&"Ölkanne"[1..];
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- unwrap_usedChecks for .unwrap() or .unwrap_err() calls on Results and .unwrap() call on Options
- module_name_repetitionsDetects public item names that are prefixed or suffixed by the containing public module’s name
- expect_usedChecks for .expect() or .expect_err() calls on Results and .expect() call on Options
- str_to_string`to_string()` called on a `&str`
- string_addyou added something to a string. Consider using `String::push_str()` instead
- string_lit_chars_anyChecks for <string_lit>.chars().any(|i| i == c)
- suspicious_xor_used_as_pow`^` is not the exponentiation operator
- tests_outside_test_moduleTriggers when a testing function (marked with the #[test] attribute) isn’t inside a testing module (marked with #[cfg(test)])
- todo`todo` should not be present in production code
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
Up next
Related lintclippy::unwrap_usedChecks for .unwrap() or .unwrap_err() calls on Results and .unwrap() call on OptionsRead it next →Did this answer your question?