Clippy lint · Pedantic · checked with Clippy 0.1.99

clippy::case_sensitive_file_extension_comparisons: case-sensitive file extension comparison

What it meansChecks for calls to ends_with with possible file extensions and suggests to use a case-insensitive approach instead. It is in the pedantic group and off by default.

What you see

warning: case-sensitive file extension comparison
 --> main.rs:4:5
  |
4 |     filename.ends_with(".rs")
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: consider using a case-insensitive comparison instead
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#case_sensitive_file_extension_comparisons
  = note: `-W clippy::case-sensitive-file-extension-comparisons` implied by `-W clippy::pedantic`
help: use std::path::Path
  |
4 ~     std::path::Path::new(filename)
5 +         .extension()
6 +         .is_some_and(|ext| ext.eq_ignore_ascii_case("rs"))
  |

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?

ends_with is case-sensitive and may not detect files with a valid extension.

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

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

fn is_rust_file(filename: &str) -> bool {
    filename.ends_with(".rs")
}

Write this instead

fn is_rust_file(filename: &str) -> bool {
    let filename = std::path::Path::new(filename);
    filename.extension()
        .map_or(false, |ext| ext.eq_ignore_ascii_case("rs"))
}

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]
case_sensitive_file_extension_comparisons = "warn"

In code

#![warn(clippy::case_sensitive_file_extension_comparisons)]

One run

cargo clippy -- -W clippy::case-sensitive-file-extension-comparisons

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

nofixed by cargo clippy --fix

1.51.0added in Rust

Clippy's own documentation

What it does

Checks for calls to ends_with with possible file extensions and suggests to use a case-insensitive approach instead.

Why is this bad?

ends_with is case-sensitive and may not detect files with a valid extension.

Example

fn is_rust_file(filename: &str) -> bool {
    filename.ends_with(".rs")
}

Use instead:

fn is_rust_file(filename: &str) -> bool {
    let filename = std::path::Path::new(filename);
    filename.extension()
        .map_or(false, |ext| ext.eq_ignore_ascii_case("rs"))
}

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

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