Clippy lint · Suspicious · checked with Clippy 0.1.99

clippy::octal_escapes: octal-looking escape in a literal

What it meansChecks for \0 escapes in string and byte literals that look like octal character escapes in C. It is in the suspicious group and warns by default.

What you see

warning: octal-looking escape in a literal
 --> main.rs:3:12
  |
3 | let one = "\033[1m Bold? \033[0m";  // \033 intended as escape
  |            ^^^^
  |
  = help: octal escapes are not supported, `\0` is always null
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#octal_escapes
  = note: `#[warn(clippy::octal_escapes)]` on by default
help: if an octal escape is intended, use a hex escape instead
  |
3 - let one = "\033[1m Bold? \033[0m";  // \033 intended as escape
3 + let one = "\x1b[1m Bold? \033[0m";  // \033 intended as escape
  |
help: if a null escape is intended, disambiguate using
  |
3 | let one = "\x0033[1m Bold? \033[0m";  // \033 intended as escape
  |             ++

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?

C and other languages support octal character escapes in strings, where a backslash is followed by up to three octal digits. For example, \033 stands for the ASCII character 27 (ESC). Rust does not support this notation, but has the escape code \0 which stands for a null byte/character, and any following digits do not form part of the escape sequence. Therefore, \033 is not a compiler error but the result may be surprising.

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

let one = "\033[1m Bold? \033[0m";  // \033 intended as escape
let two = "\033\0";                 // \033 intended as null-3-3

Write this instead

let one = "\x1b[1mWill this be bold?\x1b[0m";
let two = "\x0033\x00";

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::octal_escapes)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
octal_escapes = "allow"

One run

cargo clippy -- -A clippy::octal-escapes

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.

Suspiciousgroup

warndefault level

nofixed by cargo clippy --fix

1.59.0added in Rust

Clippy's own documentation

What it does

Checks for \0 escapes in string and byte literals that look like octal character escapes in C.

Why is this bad?

C and other languages support octal character escapes in strings, where a backslash is followed by up to three octal digits. For example, \033 stands for the ASCII character 27 (ESC). Rust does not support this notation, but has the escape code \0 which stands for a null byte/character, and any following digits do not form part of the escape sequence. Therefore, \033 is not a compiler error but the result may be surprising.

Known problems

The actual meaning can be the intended one. \x00 can be used in these cases to be unambiguous.

The lint does not trigger for format strings in print!(), write!() and friends since the string is already preprocessed when Clippy lints can see it.

Example

let one = "\033[1m Bold? \033[0m";  // \033 intended as escape
let two = "\033\0";                 // \033 intended as null-3-3

Use instead:

let one = "\x1b[1mWill this be bold?\x1b[0m";
let two = "\x0033\x00";

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

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