Clippy lint · Suspicious · checked with Clippy 0.1.99

clippy::suspicious_open_options: Checks for the suspicious use of OpenOptions::create() without an explicit OpenOptions::truncate()

What it meansChecks for the suspicious use of OpenOptions::create() without an explicit OpenOptions::truncate(). It is in the suspicious group and warns by default.

Does it matter?

create() alone will either create a new file or open an existing file. If the file already exists, it will be overwritten when written to, but the file will not be truncated by default. If less data is written to the file than it already contains, the remainder of the file will remain unchanged, and the end of the file will contain old data. In most cases, one should either use create_new to ensure the file is created from scratch, or ensure truncate is called so that the truncation behaviour is explicit. truncate(true) will ensure the file is entirely overwritten with new data, whereas truncate(false) will explicitly keep the default behavior.

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

use std::fs::OpenOptions;

OpenOptions::new().create(true);

Write this instead

use std::fs::OpenOptions;

OpenOptions::new().create(true).truncate(true);

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
suspicious_open_options = "allow"

One run

cargo clippy -- -A clippy::suspicious-open-options

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

1.77.0added in Rust

Clippy's own documentation

What it does

Checks for the suspicious use of OpenOptions::create() without an explicit OpenOptions::truncate().

Why is this bad?

create() alone will either create a new file or open an existing file. If the file already exists, it will be overwritten when written to, but the file will not be truncated by default. If less data is written to the file than it already contains, the remainder of the file will remain unchanged, and the end of the file will contain old data. In most cases, one should either use create_new to ensure the file is created from scratch, or ensure truncate is called so that the truncation behaviour is explicit. truncate(true) will ensure the file is entirely overwritten with new data, whereas truncate(false) will explicitly keep the default behavior.

Example

use std::fs::OpenOptions;

OpenOptions::new().create(true);

Use instead:

use std::fs::OpenOptions;

OpenOptions::new().create(true).truncate(true);

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

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