# Optional Oxlint plugin

Source: https://smartassertions.dev/oxlint-plugin-rules/
Index of every page: https://smartassertions.dev/llms.txt

The `@kensio/smartass` package also exports an optional
[Oxlint](https://oxc.rs/docs/guide/usage/linter.html) plugin that discourages less specific
assertion usage. For example:

```typescript
assertIdentical(foo.length, 2);
// suggested improvement:
assertArrayLength(foo, 2);
```

The plugin reports the same suggestions as the
[optional ESLint config](https://smartassertions.dev/eslint-config-rules/): both are generated from a single table of
selectors, so the two linters report identically and you only need whichever one you already run.

## Setup

The `@kensio/smartass/oxlint` export is an
[Oxlint JS plugin](https://oxc.rs/docs/guide/usage/linter/js-plugins.html). Register it under
`jsPlugins` in your `.oxlintrc.json` and turn the rule on:

```json
{
  "jsPlugins": [{ "name": "smartass", "specifier": "@kensio/smartass/oxlint" }],
  "rules": {
    "smartass/prefer-specific-assertions": "warn"
  }
}
```

The `name` you give the plugin is the prefix the rule is configured under, so a different name means
a different rule name — `"name": "sa"` would make the rule `sa/prefer-specific-assertions`.

## The rule

`smartass/prefer-specific-assertions` is the plugin's only rule. It takes no options, so `"warn"` or
`"error"` is the whole of its configuration. It reports a suggestion wherever a broad assertion is
doing a job one of the specific assertions describes better, and never rewrites your code: every
report is a message, with no fixer.

Only calls to smartass assertion functions are matched — every selector is anchored to an
`assert*` call by name, so an `expect()` or a helper of your own with a similar shape is left
alone.

Some examples of the replacements the rule will suggest:

- `assertIdentical(value, true)` → `assertTrue(value)`
- `assertIdentical(value, false)` → `assertFalse(value)`
- `assertIdentical(value, undefined)` → `assertUndefined(value)`
- `assertTrue(value != null)` → `assertNonNullable(value)`
- `assertIdentical(typeof value, "string")` → `assertTypeString(value)`
- `assertIdentical(value instanceof MyClass, true)` → `assertInstanceOf(value, MyClass)`
- `assertIdentical("key" in object, true)` → `assertObjectHasProperty(object, "key")`
- `assertIdentical(value.length, expected)` → `assertArrayLength()` etc.
- `assertIdentical(value.size, expected)` → `assertSetSize()` etc.
- `assertTrue(array.length > 0)` → `assertArrayNotEmpty(array)`
- `assertTrue(value.includes(expected))` → `assertStringIncludes()` etc.
- `assertTrue(value.startsWith(prefix))` → `assertStringStartsWith(value, prefix)`
- `assertTrue(value.endsWith(suffix))` → `assertStringEndsWith(value, suffix)`
- `assertTrue(stats.isDirectory())` → `assertDirectoryExists()` etc.

## Requirements

JS plugins are loaded from a `jsPlugins` entry, which needs an Oxlint version that supports them.
The plugin is exercised against Oxlint's own `RuleTester`, from `oxlint/plugins-dev`, on Oxlint
1.77 and later.

`@kensio/smartass/oxlint` does not depend on Oxlint itself: the plugin types are declared
structurally, so adding the plugin adds no Oxlint version constraint to your install.