clippy::missing_assert_message: Checks assertions without a custom panic message

fn call(service: Service) {
    assert!(service.ready);
}

fn call(service: Service) {
    assert!(service.ready, "`service.poll_ready()` must be called first to ensure that service is ready to receive requests");
}

[lints.clippy]
missing_assert_message = "warn"

#![warn(clippy::missing_assert_message)]

cargo clippy -- -W clippy::missing-assert-message

Clippy's own documentation

What it does

Checks assertions without a custom panic message.

Why restrict this?

Without a good custom message, it’d be hard to understand what went wrong when the assertion fails. A good custom message should be more about why the failure of the assertion is problematic and not what is failed because the assertion already conveys that.

Although the same reasoning applies to testing functions, this lint ignores them as they would be too noisy. Also, in most cases understanding the test failure would be easier compared to understanding a complex invariant distributed around the codebase.

Known problems

This lint cannot check the quality of the custom panic messages. Hence, you can suppress this lint simply by adding placeholder messages like “assertion failed”. However, we recommend coming up with good messages that provide useful information instead of placeholder messages that don’t provide any extra information.

Example

fn call(service: Service) {
    assert!(service.ready);
}

Use instead:

fn call(service: Service) {
    assert!(service.ready, "`service.poll_ready()` must be called first to ensure that service is ready to receive requests");
}

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
• map_with_unused_argument_over_rangesmap of a closure that does not depend on its parameter over a range
• mem_forgetChecks for usage of std::mem::forget(t) where t is Drop or has a field that implements Drop
• min_ident_charsChecks for identifiers which consist of a single character (or fewer than the configured threshold). Note: This lint can be very noisy when enabled; it may be desirable to only enable it temporarily
• missing_asserts_for_indexingindexing into a slice multiple times without an `assert`
• missing_docs_in_private_itemsWarns if there is missing documentation for any private documentable item
• missing_inline_in_public_itemsmissing `#[inline]` on a publicly callable function

All 847 Clippy lints · Rust compiler errors · Cargo.toml checker