oxc-project/oxc · warning · OxcDiagnostic

Expected expression to be used

Error message

Expected expression to be used

What it means

Diagnostic from oxlint's no-unused-expressions rule. An expression statement that only computes and discards a value has no effect and usually hides a missing call, assignment, or cast. Options: allowShortCircuit (a && b()), allowTernary (a ? b() : c()), allowTaggedTemplates, enforceForJSX, and ignoreDirectives for directive prologues.

Source

Thrown at crates/oxc_linter/src/rules/eslint/no_unused_expressions.rs:19

use oxc_ast::{
    AstKind,
    ast::{ChainElement, Expression, UnaryOperator},
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::Span;
use schemars::JsonSchema;
use serde::Deserialize;
use serde_json::Value;

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

fn no_unused_expressions_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Expected expression to be used")
        .with_help("Consider using this expression or removing it")
        .with_label(span)
}

#[derive(Debug, Default, Clone, Deserialize)]
pub struct NoUnusedExpressions(Box<NoUnusedExpressionsConfig>);

#[derive(Debug, Default, Clone, JsonSchema, Deserialize)]
#[serde(rename_all = "camelCase", default, deny_unknown_fields)]
pub struct NoUnusedExpressionsConfig {
    /// When set to `true`, allows short circuit evaluations in expressions.
    allow_short_circuit: bool,
    /// When set to `true`, allows ternary operators in expressions.
    allow_ternary: bool,
    /// When set to `true`, allows tagged template literals in expressions.
    allow_tagged_templates: bool,
    /// When set to `true`, enforces the rule for unused JSX expressions also.
    #[serde(rename = "enforceForJSX")]

View on GitHub (pinned to e1e7af627c)

Solutions

1. Delete the statement or give it an effect (call it, assign it, export it).
2. Enable "allowShortCircuit": true for a && b() style and "allowTernary": true for side-effectful ternaries in .oxlintrc.json.
3. Convert the ternary to if/else when you do not want to relax the rule.
4. Wrap intended template tags with "allowTaggedTemplates": true (e.g. gql`...`).

Example fix

// before
isReady && bootstrap();
// after
if (isReady) bootstrap();
// or .oxlintrc.json: "no-unused-expressions": ["error", { "allowShortCircuit": true }]

When it happens

Trigger: Set<number>; as a bare statement; 1 as number; window!; a + b; isReady && bootstrap(); without allowShortCircuit; cond ? f() : g(); without allowTernary.

Common situations: Guard-style short-circuit calls in a codebase where the options are off; leftover probe expressions from debugging; non-null assertions and type casts used as statements.

Related errors

• Expected method{method_name_str} to have this.
• {prefix} {{ after '{keyword}'{condition_if_needed}.
• Enforce default clauses in switch statements to be last
• Expected a function {style}.
• Accessor pair {getter_key} and {setter_key} should be groupe

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/a402b386f5711c73. Report an issue: GitHub.