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fix(linter): Fix default behavior of the eslint/eqeqeq rule, and also the config option docs for it #16560

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Merged
camchenry merged 6 commits into from
Dec 10, 2025
Merged

fix(linter): Fix default behavior of the eslint/eqeqeq rule, and also the config option docs for it #16560

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ee262b3
Reorganize eqeqeq a bit.
connorshea Dec 6, 2025
ed59871
fix(linter): Update eqeqeq rule to use DefaultRuleConfig and have cor…
connorshea Dec 6, 2025
353d993
fix(linter): Fix test in eqeqeq rule.
connorshea Dec 6, 2025
0cc24ef
Simplify the code a bit and handle defaults via serde.
connorshea Dec 6, 2025
2cf8229
Improve docs.
connorshea Dec 6, 2025
2ba5292
Fix phrasing.
connorshea Dec 6, 2025
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151 changes: 60 additions & 91 deletions crates/oxc_linter/src/rules/eslint/eqeqeq.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,21 +7,54 @@ use oxc_macros::declare_oxc_lint;
use oxc_span::{GetSpan, Span};
use oxc_syntax::operator::{BinaryOperator, UnaryOperator};
use schemars::JsonSchema;
use serde::Deserialize;

use crate::fixer::{RuleFix, RuleFixer};
use crate::{AstNode, context::LintContext, rule::Rule};
use crate::{
fixer::{RuleFix, RuleFixer},
rule::DefaultRuleConfig,
};

fn eqeqeq_diagnostic(actual: &str, expected: &str, span: Span) -> OxcDiagnostic {
OxcDiagnostic::warn(format!("Expected {expected} and instead saw {actual}"))
.with_help(format!("Prefer {expected} operator"))
.with_label(span)
}

#[derive(Debug, Default, Clone, JsonSchema)]
#[derive(Debug, Default, Clone, JsonSchema, Deserialize)]
#[serde(rename_all = "camelCase", default)]
pub struct Eqeqeq(CompareType, EqeqeqOptions);

#[derive(Debug, Default, Clone, JsonSchema, Deserialize)]
#[serde(rename_all = "camelCase", default)]
pub struct Eqeqeq {
compare_type: CompareType,
null_type: NullType,
pub struct EqeqeqOptions {
/// Configuration for whether to allow/disallow comparisons against `null`,
/// e.g. `foo == null` or `foo != null`
null: NullType,
}

#[derive(Debug, Default, Clone, JsonSchema, Deserialize)]
#[serde(rename_all = "kebab-case")]
enum CompareType {
/// Always require triple-equal comparisons, `===`/`!==`.
/// This is the default.
#[default]
Always,
/// Allow certain safe comparisons to use `==`/`!=` (`typeof`, literals, nullish).
Smart,
}

#[derive(Debug, Default, Clone, JsonSchema, Deserialize)]
#[serde(rename_all = "kebab-case")]
enum NullType {
/// Always require triple-equals when comparing with null, `=== null`/`!== null`.
/// This is the default.
#[default]
Always,
/// Never require triple-equals when comparing with null, always use `== null`/`!= null`.
Never,
/// Ignore null comparisons, allow either `== null`/`!= null` or `=== null`/`!== null`.
Ignore,
}

declare_oxc_lint!(
Expand All @@ -35,24 +68,6 @@ declare_oxc_lint!(
///
/// ### Options
///
/// First option:
/// - Type: `string`
/// - Default: `"always"`
///
/// Possible values:
/// * `"always"` - always require `===`/`!==`
/// * `"smart"` - allow safe comparisons (`typeof`, literals, nullish)
///
/// Second option (only used with `"always"`):
/// - Type: `object`
/// - Properties:
/// - `null`: `string` (default: `"always"`) - `"ignore"` allows `== null` and `!= null`.
///
/// Possible values for `null`:
/// * `"always"` - always require `=== null`/`!== null`
/// * `"never"` - always require `== null`/`!= null`
/// * `"ignore"` - allow both `== null`/`!= null` and `=== null`/`!== null`
///
/// Example JSON configuration:
/// ```json
/// {
Expand All @@ -66,7 +81,7 @@ declare_oxc_lint!(
///
/// Examples of **incorrect** code for this rule:
/// ```js
/// /* eslint eqeqeq: "error" */
/// /* eqeqeq: "error" */
///
/// if (x == 42) {}
/// if ("" == text) {}
Expand All @@ -75,7 +90,7 @@ declare_oxc_lint!(
///
/// Examples of **correct** code for this rule:
/// ```js
/// /* eslint eqeqeq: "error" */
/// /* eqeqeq: "error" */
///
/// if (x === 42) {}
/// if ("" === text) {}
Expand All @@ -86,15 +101,15 @@ declare_oxc_lint!(
///
/// Examples of **incorrect** code for this rule with the `"smart"` option:
/// ```js
/// /* eslint eqeqeq: ["error", "smart"] */
/// /* eqeqeq: ["error", "smart"] */
///
/// if (x == 42) {}
/// if ("" == text) {}
/// ```
///
/// Examples of **correct** code for this rule with the `"smart"` option:
/// ```js
/// /* eslint eqeqeq: ["error", "smart"] */
/// /* eqeqeq: ["error", "smart"] */
///
/// if (typeof foo == "undefined") {}
/// if (foo == null) {}
Expand All @@ -105,14 +120,14 @@ declare_oxc_lint!(
///
/// Examples of **incorrect** code for this rule with the `{ "null": "ignore" }` option:
/// ```js
/// /* eslint eqeqeq: ["error", "always", { "null": "ignore" }] */
/// /* eqeqeq: ["error", "always", { "null": "ignore" }] */
/// if (x == 42) {}
/// if ("" == text) {}
/// ```
///
/// Examples of **correct** code for this rule with the `{ "null": "ignore" }` option:
/// ```js
/// /* eslint eqeqeq: ["error", "always", { "null": "ignore" }] */
/// /* eqeqeq: ["error", "always", { "null": "ignore" }] */
/// if (foo == null) {}
/// if (foo != null) {}
/// ```
Expand All @@ -121,15 +136,15 @@ declare_oxc_lint!(
///
/// Examples of **incorrect** code for this rule with the `{ "null": "always" }` option:
/// ```js
/// /* eslint eqeqeq: ["error", "always", { "null": "always" }] */
/// /* eqeqeq: ["error", "always", { "null": "always" }] */
///
/// if (foo == null) {}
/// if (foo != null) {}
/// ```
///
/// Examples of **correct** code for this rule with the `{ "null": "always" }` option:
/// ```js
/// /* eslint eqeqeq: ["error", "always", { "null": "always" }] */
/// /* eqeqeq: ["error", "always", { "null": "always" }] */
///
/// if (foo === null) {}
/// if (foo !== null) {}
Expand All @@ -139,7 +154,7 @@ declare_oxc_lint!(
///
/// Examples of **incorrect** code for this rule with the `{ "null": "never" }` option:
/// ```js
/// /* eslint eqeqeq: ["error", "always", { "null": "never" }] */
/// /* eqeqeq: ["error", "always", { "null": "never" }] */
///
/// if (x == 42) {}
/// if ("" == text) {}
Expand All @@ -149,60 +164,23 @@ declare_oxc_lint!(
///
/// Examples of **correct** code for this rule with the `{ "null": "never" }` option:
/// ```js
/// /* eslint eqeqeq: ["error", "always", { "null": "never" }] */
/// /* eqeqeq: ["error", "always", { "null": "never" }] */
///
/// if (x === 42) {}
/// if ("" === text) {}
/// if (foo == null) {}
/// if (foo != null) {}
/// ```
///
Eqeqeq,
eslint,
pedantic,
fix = conditional_fix_dangerous,
config = Eqeqeq,
);

#[derive(Debug, Default, Clone, JsonSchema)]
#[serde(rename_all = "lowercase")]
enum CompareType {
#[default]
Always,
Smart,
}

impl CompareType {
pub fn from(raw: &str) -> Self {
match raw {
"smart" => Self::Smart,
_ => Self::Always,
}
}
}

#[derive(Debug, Default, Clone, JsonSchema)]
#[serde(rename_all = "lowercase")]
enum NullType {
#[default]
Always,
Never,
Ignore,
}

impl NullType {
pub fn from(raw: &str) -> Self {
match raw {
"always" => Self::Always,
"never" => Self::Never,
_ => Self::Ignore,
}
}
}

impl Eqeqeq {
fn report_inverse_null_comparison(&self, binary_expr: &BinaryExpression, ctx: &LintContext) {
if !matches!(self.null_type, NullType::Never) {
if !matches!(self.1.null, NullType::Never) {
return;
}
let operator = binary_expr.operator.as_str();
Expand All @@ -216,26 +194,17 @@ impl Eqeqeq {

impl Rule for Eqeqeq {
fn from_configuration(value: serde_json::Value) -> Self {
let first_arg = value.get(0).and_then(serde_json::Value::as_str);

let null_type = value
.get(usize::from(first_arg.is_some()))
.and_then(|v| v.get("null"))
.and_then(serde_json::Value::as_str)
.map(NullType::from)
.unwrap_or_default();

let compare_type = first_arg.map(CompareType::from).unwrap_or_default();

Self { compare_type, null_type }
serde_json::from_value::<DefaultRuleConfig<Eqeqeq>>(value).unwrap_or_default().into_inner()
}

fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
let AstKind::BinaryExpression(binary_expr) = node.kind() else {
return;
};
let Eqeqeq(compare_type, options) = self.clone();

let is_null_comparison = is_null_check(binary_expr);
let must_enforce_null = matches!(self.null_type, NullType::Always);
let must_enforce_null = matches!(options.null, NullType::Always);

if !matches!(binary_expr.operator, BinaryOperator::Equality | BinaryOperator::Inequality) {
if is_null_comparison {
Expand All @@ -251,7 +220,7 @@ impl Rule for Eqeqeq {
// - Comparing two literal values
// - Evaluating the value of typeof
// - Comparing against null
if matches!(self.compare_type, CompareType::Smart)
if matches!(compare_type, CompareType::Smart)
&& (is_typeof_check || is_same_type_literals || is_null_comparison)
{
return;
Expand Down Expand Up @@ -361,18 +330,18 @@ fn test() {
("foo == null", Some(json!(["smart"]))),
("foo === null", None),
// Always use === or !== with `null`
("null === null", Some(json!(["always", {"null": "always"}]))),
("null === null", Some(json!(["always", { "null": "always" }]))),
// Never use === or !== with `null`
("null == null", Some(json!(["always", {"null": "never"}]))),
("null == null", Some(json!(["always", { "null": "never" }]))),
// Do not apply this rule to `null`.
("null == null", Some(json!(["smart", {"null": "ignore"}]))),
("null == null", Some(json!(["smart", { "null": "ignore" }]))),
// Issue: <https://github.com/oxc-project/oxc/issues/8773>
("href != null", Some(json!([{"null": "ignore"}]))),
("href != null", Some(json!(["always", { "null": "ignore" }]))),
];

let fail = vec![
// ESLint will perform like below case
("null >= 1", Some(json!(["always", {"null": "never"}]))),
("null >= 1", Some(json!(["always", { "null": "never" }]))),
("typeof foo == 'undefined'", None),
("'hello' != 'world'", None),
("0 == 0", None),
Expand All @@ -382,7 +351,7 @@ fn test() {
("foo == true", None),
("bananas != 1", None),
("value == undefined", None),
("null == null", Some(json!(["always", {"null": "always"}]))),
("null == null", Some(json!(["always", { "null": "always" }]))),
];

let fix = vec![
Expand Down
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