feat(linter): implement unicorn/no-negation-in-equality-check (#4034)

Fixes https://github.com/oxc-project/oxc/issues/3869

Hey there, thought I'd give this a try as it's tagged "good first issue"
:) Let me know if there's anything that needs to change, I wasn't sure
about the rule category so left as TODO.

crates/oxc_linter/src/rules.rs

@@ -260,6 +260,7 @@ mod unicorn {
     pub mod no_lonely_if;
     pub mod no_magic_array_flat_depth;
     pub mod no_negated_condition;
+    pub mod no_negation_in_equality_check;
     pub mod no_nested_ternary;
     pub mod no_new_array;
     pub mod no_new_buffer;
@@ -619,6 +620,7 @@ oxc_macros::declare_all_lint_rules! {
     unicorn::no_lonely_if,
     unicorn::no_magic_array_flat_depth,
     unicorn::no_negated_condition,
+    unicorn::no_negation_in_equality_check,
     unicorn::no_nested_ternary,
     unicorn::no_new_array,
     unicorn::no_new_buffer,

crates/oxc_linter/src/rules/unicorn/no_negation_in_equality_check.rs

@@ -0,0 +1,135 @@
+use oxc_ast::{ast::Expression, AstKind};
+use oxc_diagnostics::OxcDiagnostic;
+use oxc_macros::declare_oxc_lint;
+use oxc_span::Span;
+use oxc_syntax::operator::{BinaryOperator, UnaryOperator};
+
+use crate::{context::LintContext, rule::Rule, AstNode};
+
+fn no_negation_in_equality_check_diagnostic(
+    span0: Span,
+    current_operator: BinaryOperator,
+    suggested_operator: BinaryOperator,
+) -> OxcDiagnostic {
+    OxcDiagnostic::warn(
+        "eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.",
+    )
+    .with_help(format!("Remove the negation operator and use '{}' instead of '{}'.", suggested_operator.as_str(), current_operator.as_str()))
+    .with_label(span0)
+}
+
+#[derive(Debug, Default, Clone)]
+pub struct NoNegationInEqualityCheck;
+
+declare_oxc_lint!(
+    /// ### What it does
+    ///
+    /// Disallow negated expressions on the left of (in)equality checks.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// A negated expression on the left of an (in)equality check is likely a mistake from trying to negate the whole condition.
+    ///
+    /// ### Example
+    /// ```javascript
+    /// // Bad
+    ///
+    /// if (!foo === bar) {}
+    ///
+    /// if (!foo !== bar) {}
+    ///
+    /// // Good
+    ///
+    /// if (foo !== bar) {}
+    ///
+    /// if (!(foo === bar)) {}
+    /// ```
+    NoNegationInEqualityCheck,
+    correctness,
+);
+
+impl Rule for NoNegationInEqualityCheck {
+    fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
+        if let AstKind::BinaryExpression(binary_expr) = node.kind() {
+            let Expression::UnaryExpression(left_unary_expr) = &binary_expr.left else {
+                return;
+            };
+
+            if left_unary_expr.operator != UnaryOperator::LogicalNot {
+                return;
+            }
+
+            if let Expression::UnaryExpression(left_nested_unary_expr) = &left_unary_expr.argument {
+                if left_nested_unary_expr.operator == UnaryOperator::LogicalNot {
+                    return;
+                }
+            }
+
+            if !binary_expr.operator.is_equality() {
+                return;
+            }
+
+            let Some(suggested_operator) = binary_expr.operator.equality_inverse_operator() else {
+                return;
+            };
+
+            ctx.diagnostic(no_negation_in_equality_check_diagnostic(
+                left_unary_expr.span,
+                binary_expr.operator,
+                suggested_operator,
+            ));
+        }
+    }
+}
+
+#[test]
+fn test() {
+    use crate::tester::Tester;
+
+    let pass = vec![
+        "!foo instanceof bar",
+        "+foo === bar",
+        "!(foo === bar)",
+        "!!foo === bar",
+        "!!!foo === bar",
+        "foo === !bar",
+    ];
+
+    let fail = vec![
+        "!foo === bar",
+        "!foo !== bar",
+        "!foo == bar",
+        "!foo != bar",
+        "
+						function x() {
+							return!foo === bar;
+						}
+					",
+        "
+						function x() {
+							return!
+								foo === bar;
+							throw!
+								foo === bar;
+						}
+					",
+        "
+						foo
+						!(a) === b
+					",
+        "
+						foo
+						![a, b].join('') === c
+					",
+        "
+						foo
+						! [a, b].join('') === c
+					",
+        "
+						foo
+						!/* comment */[a, b].join('') === c
+					",
+    ];
+
+    Tester::new(NoNegationInEqualityCheck::NAME, pass, fail).test_and_snapshot();
+}

crates/oxc_linter/src/snapshots/no_negation_in_equality_check.snap

@@ -0,0 +1,93 @@
+---
+source: crates/oxc_linter/src/tester.rs
+---
+  ⚠ eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.
+   ╭─[no_negation_in_equality_check.tsx:1:1]
+ 1 │ !foo === bar
+   · ────
+   ╰────
+  help: Remove the negation operator and use '!==' instead of '==='.
+
+  ⚠ eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.
+   ╭─[no_negation_in_equality_check.tsx:1:1]
+ 1 │ !foo !== bar
+   · ────
+   ╰────
+  help: Remove the negation operator and use '===' instead of '!=='.
+
+  ⚠ eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.
+   ╭─[no_negation_in_equality_check.tsx:1:1]
+ 1 │ !foo == bar
+   · ────
+   ╰────
+  help: Remove the negation operator and use '!=' instead of '=='.
+
+  ⚠ eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.
+   ╭─[no_negation_in_equality_check.tsx:1:1]
+ 1 │ !foo != bar
+   · ────
+   ╰────
+  help: Remove the negation operator and use '==' instead of '!='.
+
+  ⚠ eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.
+   ╭─[no_negation_in_equality_check.tsx:3:14]
+ 2 │                         function x() {
+ 3 │                             return!foo === bar;
+   ·                                   ────
+ 4 │                         }
+   ╰────
+  help: Remove the negation operator and use '!==' instead of '==='.
+
+  ⚠ eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.
+   ╭─[no_negation_in_equality_check.tsx:3:14]
+ 2 │                             function x() {
+ 3 │ ╭─▶                             return!
+ 4 │ ╰─▶                                 foo === bar;
+ 5 │                                 throw!
+   ╰────
+  help: Remove the negation operator and use '!==' instead of '==='.
+
+  ⚠ eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.
+   ╭─[no_negation_in_equality_check.tsx:5:13]
+ 4 │                                     foo === bar;
+ 5 │ ╭─▶                             throw!
+ 6 │ ╰─▶                                 foo === bar;
+ 7 │                             }
+   ╰────
+  help: Remove the negation operator and use '!==' instead of '==='.
+
+  ⚠ eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.
+   ╭─[no_negation_in_equality_check.tsx:3:7]
+ 2 │                         foo
+ 3 │                         !(a) === b
+   ·                         ────
+ 4 │                     
+   ╰────
+  help: Remove the negation operator and use '!==' instead of '==='.
+
+  ⚠ eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.
+   ╭─[no_negation_in_equality_check.tsx:3:7]
+ 2 │                         foo
+ 3 │                         ![a, b].join('') === c
+   ·                         ────────────────
+ 4 │                     
+   ╰────
+  help: Remove the negation operator and use '!==' instead of '==='.
+
+  ⚠ eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.
+   ╭─[no_negation_in_equality_check.tsx:3:7]
+ 2 │                         foo
+ 3 │                         ! [a, b].join('') === c
+   ·                         ─────────────────
+ 4 │                     
+   ╰────
+  help: Remove the negation operator and use '!==' instead of '==='.
+
+  ⚠ eslint-plugin-unicorn(no-negation-in-equality-check): Negated expression is not allowed in equality check.
+   ╭─[no_negation_in_equality_check.tsx:3:7]
+ 2 │                         foo
+ 3 │                         !/* comment */[a, b].join('') === c
+   ·                         ─────────────────────────────
+ 4 │                     
+   ╰────
+  help: Remove the negation operator and use '!==' instead of '==='.