Clippy lint · Suspicious · checked with Clippy 0.1.99

clippy::ineffective_open_options: Checks if both .write(true) and .append(true) methods are called on a same OpenOptions

What it meansChecks if both .write(true) and .append(true) methods are called on a same OpenOptions. It is in the suspicious group and warns by default.

Does it matter?

.append(true) already enables write(true), making this one superfluous.

Code that is most likely wrong or useless. Warns by default.

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

let _ = OpenOptions::new()
           .write(true)
           .append(true)
           .create(true)
           .open("file.json");

Write this instead

let _ = OpenOptions::new()
           .append(true)
           .create(true)
           .open("file.json");

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
ineffective_open_options = "allow"

One run

cargo clippy -- -A clippy::ineffective-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

yesfixed by cargo clippy --fix

1.76.0added in Rust

Clippy's own documentation

What it does

Checks if both .write(true) and .append(true) methods are called on a same OpenOptions.

Why is this bad?

.append(true) already enables write(true), making this one superfluous.

Example

let _ = OpenOptions::new()
           .write(true)
           .append(true)
           .create(true)
           .open("file.json");

Use instead:

let _ = OpenOptions::new()
           .append(true)
           .create(true)
           .open("file.json");

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

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