feat(linter): implement no-nested-ternary rule

crates/oxc_linter/src/rules.rs

@@ -93,6 +93,7 @@ mod eslint {
     pub mod no_loss_of_precision;
     pub mod no_magic_numbers;
     pub mod no_multi_str;
+    pub mod no_nested_ternary;
     pub mod no_new;
     pub mod no_new_func;
     pub mod no_new_native_nonconstructor;
@@ -535,6 +536,7 @@ oxc_macros::declare_all_lint_rules! {
     eslint::max_classes_per_file,
     eslint::max_lines,
     eslint::max_params,
+    eslint::no_nested_ternary,
     eslint::no_labels,
     eslint::no_restricted_imports,
     eslint::no_object_constructor,

crates/oxc_linter/src/rules/eslint/no_nested_ternary.rs

@@ -0,0 +1,103 @@
+use oxc_ast::ast::Expression;
+use oxc_ast::AstKind;
+use oxc_diagnostics::OxcDiagnostic;
+use oxc_macros::declare_oxc_lint;
+use oxc_span::Span;
+
+use crate::{context::LintContext, rule::Rule, AstNode};
+
+fn no_nested_ternary_diagnostic(span: Span) -> OxcDiagnostic {
+    OxcDiagnostic::warn("Do not nest ternary expressions.").with_label(span)
+}
+
+#[derive(Debug, Default, Clone)]
+pub struct NoNestedTernary;
+
+declare_oxc_lint!(
+    /// ### What it does
+    ///
+    /// Disallows nested ternary expressions to improve code readability and maintainability.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// Nested ternary expressions make code harder to read and understand. They can lead to complex, difficult-to-debug logic.
+    ///
+    /// ### Examples
+    ///
+    /// Examples of **incorrect** code for this rule:
+    /// ```js
+    /// const result = condition1 ? (condition2 ? "a" : "b") : "c";
+    /// ```
+    ///
+    /// Examples of **correct** code for this rule:
+    /// ```js
+    /// let result;
+    /// if (condition1) {
+    ///   result = condition2 ? "a" : "b";
+    /// } else {
+    ///   result = "c";
+    /// }
+    /// ```
+    NoNestedTernary,
+    style,
+);
+
+impl Rule for NoNestedTernary {
+    fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
+        if let AstKind::ConditionalExpression(node) = node.kind() {
+            let check_nested_ternary = |expr: &Expression| {
+                if matches!(expr, Expression::ConditionalExpression(_)) {
+                    true
+                } else {
+                    let inner_expr = expr.get_inner_expression();
+                    matches!(inner_expr, Expression::ConditionalExpression(_))
+                }
+            };
+
+            if check_nested_ternary(&node.consequent) || check_nested_ternary(&node.alternate) {
+                ctx.diagnostic(no_nested_ternary_diagnostic(node.span));
+            }
+        }
+    }
+}
+
+#[test]
+fn test() {
+    use crate::tester::Tester;
+
+    let pass = vec![
+        "foo ? doBar() : doBaz();",
+        "var foo = bar === baz ? qux : quxx;",
+        "var result = foo && bar ? baz : qux || quux;",
+        "var result = foo ? bar : baz === qux;",
+        "foo ? doSomething(a, b) : doSomethingElse(c, d);",
+        // Parenthesized Expressions
+        "var result = (foo ? bar : baz) || qux;",
+        "var result = (foo ? bar : baz) && qux;",
+        "var result = foo === bar ? (baz || qux) : quux;",
+        "var result = (foo ? bar : baz) ? qux : quux;",
+        // TypeScript
+        "var result = foo! ? bar : baz;",
+        "var result = foo ? bar! : baz;",
+        "var result = (foo as boolean) ? bar : baz;",
+        "var result = foo ? (bar as string) : baz;",
+    ];
+
+    let fail = vec![
+        "foo ? bar : baz === qux ? quxx : foobar;",
+        "foo ? baz === qux ? quxx : foobar : bar;",
+        // Parenthesized Expressions
+        "var result = foo ? (bar ? baz : qux) : quux;",
+        "var result = foo ? (bar === baz ? qux : quux) : foobar;",
+        "doSomething(foo ? bar : baz ? qux : quux);",
+        // Comment
+        "var result = foo /* comment */ ? bar : baz ? qux : quux;",
+        // TypeScript
+        "var result = foo! ? bar : baz! ? qux : quux;",
+        "var result = foo ? bar! : (baz! ? qux : quux);",
+        "var result = (foo as boolean) ? bar : (baz as string) ? qux : quux;",
+        "var result = foo ? (bar as string) : (baz as number ? qux : quux);",
+    ];
+
+    Tester::new(NoNestedTernary::NAME, NoNestedTernary::CATEGORY, pass, fail).test_and_snapshot();
+}

crates/oxc_linter/src/snapshots/eslint_no_nested_ternary.snap

@@ -0,0 +1,63 @@
+---
+source: crates/oxc_linter/src/tester.rs
+snapshot_kind: text
+---
+  ⚠ eslint(no-nested-ternary): Do not nest ternary expressions.
+   ╭─[no_nested_ternary.tsx:1:1]
+ 1 │ foo ? bar : baz === qux ? quxx : foobar;
+   · ───────────────────────────────────────
+   ╰────
+
+  ⚠ eslint(no-nested-ternary): Do not nest ternary expressions.
+   ╭─[no_nested_ternary.tsx:1:1]
+ 1 │ foo ? baz === qux ? quxx : foobar : bar;
+   · ───────────────────────────────────────
+   ╰────
+
+  ⚠ eslint(no-nested-ternary): Do not nest ternary expressions.
+   ╭─[no_nested_ternary.tsx:1:14]
+ 1 │ var result = foo ? (bar ? baz : qux) : quux;
+   ·              ──────────────────────────────
+   ╰────
+
+  ⚠ eslint(no-nested-ternary): Do not nest ternary expressions.
+   ╭─[no_nested_ternary.tsx:1:14]
+ 1 │ var result = foo ? (bar === baz ? qux : quux) : foobar;
+   ·              ─────────────────────────────────────────
+   ╰────
+
+  ⚠ eslint(no-nested-ternary): Do not nest ternary expressions.
+   ╭─[no_nested_ternary.tsx:1:13]
+ 1 │ doSomething(foo ? bar : baz ? qux : quux);
+   ·             ────────────────────────────
+   ╰────
+
+  ⚠ eslint(no-nested-ternary): Do not nest ternary expressions.
+   ╭─[no_nested_ternary.tsx:1:14]
+ 1 │ var result = foo /* comment */ ? bar : baz ? qux : quux;
+   ·              ──────────────────────────────────────────
+   ╰────
+
+  ⚠ eslint(no-nested-ternary): Do not nest ternary expressions.
+   ╭─[no_nested_ternary.tsx:1:14]
+ 1 │ var result = foo! ? bar : baz! ? qux : quux;
+   ·              ──────────────────────────────
+   ╰────
+
+  ⚠ eslint(no-nested-ternary): Do not nest ternary expressions.
+   ╭─[no_nested_ternary.tsx:1:14]
+ 1 │ var result = foo ? bar! : (baz! ? qux : quux);
+   ·              ────────────────────────────────
+   ╰────
+
+  ⚠ eslint(no-nested-ternary): Do not nest ternary expressions.
+   ╭─[no_nested_ternary.tsx:1:14]
+ 1 │ var result = (foo as boolean) ? bar : (baz as string) ? qux : quux;
+   ·              ─────────────────────────────────────────────────────
+   ╰────
+
+  ⚠ eslint(no-nested-ternary): Do not nest ternary expressions.
+   ╭─[no_nested_ternary.tsx:1:14]
+ 1 │ var result = foo ? (bar as string) : (baz as number ? qux : quux);
+   ·              ────────────────────────────────────────────────────
+   ╰────