oxc-project/oxc · info · OxcDiagnostic

Unnecessary use of conditional expression for default assign

Error message

Unnecessary use of conditional expression for default assignment

What it means

The second `no-unneeded-ternary` diagnostic, from `no_unneeded_ternary_conditional_expression_diagnostic`: it reports the default-assignment pattern `x ? x : y` when the rule's `defaultAssignment` option is set to `false` (default `true` allows it). The help text recommends removing the ternary and using the variable directly — i.e. the logical OR `x || y` (or `?? y` for nullish-only defaults).

Source

Thrown at crates/oxc_linter/src/rules/eslint/no_unneeded_ternary.rs:23

};
use oxc_ast::{
    AstKind,
    ast::{BinaryOperator, Expression},
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::{GetSpan, Span};
use schemars::JsonSchema;
use serde::Deserialize;

fn no_unneeded_ternary_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Unnecessary use of boolean literals in conditional expression")
        .with_help("Remove this ternary operator")
        .with_label(span)
}

fn no_unneeded_ternary_conditional_expression_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Unnecessary use of conditional expression for default assignment")
        .with_help("Remove this ternary operator and use the variable directly")
        .with_label(span)
}

#[derive(Debug, Clone, JsonSchema, Deserialize)]
#[serde(rename_all = "camelCase", default, deny_unknown_fields)]
pub struct NoUnneededTernary {
    /// Whether to allow the default assignment pattern `x ? x : y`.
    ///
    /// When set to `false`, the rule also flags cases like `x ? x : y` and suggests using
    /// the logical OR form `x || y` instead. When `true` (default), such default assignments
    /// are allowed and not reported.
    default_assignment: bool,
}

impl Default for NoUnneededTernary {
    fn default() -> Self {
        Self { default_assignment: true }

View on GitHub (pinned to e1e7af627c)

Solutions

1. Replace with logical OR: `foo(bar || 1)`.
2. If only null/undefined should trigger the default, use nullish coalescing: `input ?? 'default'` (safer for `0`/`''`).
3. If the ternary form is your team's accepted style, set `defaultAssignment: true` in the rule config.

Example fix

// before
const port = config.port ? config.port : 3000;

// after
const port = config.port ?? 3000;

# find default-assignment ternaries before turning on defaultAssignment: false
rg -n '\?\s*([A-Za-z_$][\w$]*)\s*:\s' src/ | rg '\1'

When it happens

Trigger: Enabling `"no-unneeded-ternary": ["error", { "defaultAssignment": false }]` and writing `foo(bar ? bar : 1)` or `const v = input ? input : 'default'`.

Common situations: Teams standardizing on `||`/`??` for defaults turning on this option; codebases migrating from older ternary-default idioms to nullish coalescing; config option discovered after upgrading oxlint versions where the option was added.

Related errors

• Unnecessary use of boolean literals in conditional expressio
• Empty array binding pattern
• Empty object binding pattern
• Expected method{method_name_str} to have this.
• {name} has a complexity of {complexity}. Maximum allowed is

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/71833c27a399b624. Report an issue: GitHub.