Lints - The Cargo Book

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# Lints

Note: Cargo’s linting system is unstable and can only be used on nightly toolchains

## Warn-by-default

These lints are all set to the ‘warn’ level by default.

- `blanket_hint_mostly_unused`
- `unknown_lints`

## `blanket_hint_mostly_unused`

Set to `warn` by default

### What it does

Checks if `hint-mostly-unused` being applied to all dependencies.

### Why it is bad

`hint-mostly-unused` indicates that most of a crate’s API surface will go unused by anything depending on it; this hint can speed up the build by attempting to minimize compilation time for items that aren’t used at all. Misapplication to crates that don’t fit that criteria will slow down the build rather than speeding it up. It should be selectively applied to dependencies that meet these criteria. Applying it globally is always a misapplication and will likely slow down the build.

### Example

    [profile.dev.package."*"]
    hint-mostly-unused = true

Should instead be:

    [profile.dev.package.huge-mostly-unused-dependency]
    hint-mostly-unused = true

## `unknown_lints`

Set to `warn` by default

### What it does

Checks for unknown lints in the `[lints.cargo]` table

### Why it is bad

- The lint name could be misspelled, leading to confusion as to why it is not working as expected
- The unknown lint could end up causing an error if `cargo` decides to make a lint with the same name in the future

### Example

    [lints.cargo]
    this-lint-does-not-exist = "warn"