oxc-project/oxc · error · OxcDiagnostic

No duplicate props allowed. The prop

Error message

No duplicate props allowed. The prop "{prop_name}" is duplicated.

What it means

Diagnostic from react/jsx-no-duplicate-props (category: correctness). The same attribute name appears twice on one JSX opening element; the diagnostic carries labels on both the original and duplicate spans. React silently applies only the last duplicate prop, so a duplicate almost always hides a bug rather than being intentional. Note: this oxc port intentionally does NOT support the ignoreCase option — props are compared case-sensitively, so <App foo Foo /> is not flagged.

Solutions

1. Delete one of the duplicated attributes, keeping the intended value (remember React uses the LAST occurrence)
2. If the duplicate comes from a merge conflict, re-resolve the conflict instead of keeping both sides
3. If you were relying on eslint-plugin-react's ignoreCase, note it is unsupported here: make casing consistent instead
4. Add a pre-commit oxlint run so duplicates never land

Example fix

// before
<App a="1" b="2" a="3" />

// after
<App a="3" b="2" />

npx oxlint -D react/jsx-no-duplicate-props src/

When it happens

Trigger: <App a a />, <App foo={2} bar baz foo={3} />, <App a="a" {...this.props} a="a" /> — i.e. the same JSXAttribute identifier name occurring twice among the element's attributes (spread attributes are skipped, only plain attributes are tracked in a name->span map).

Common situations: Merging props from multiple sources during refactor (base props + override props copy-pasted); long attribute lists where a prop is added twice by different people; class components migrating defaultProps inline; merge conflicts duplicating an attribute block.

Related errors

• Invalid handler prop name
• Bad handler name
• `button` elements must have a valid `type` attribute.
• `button` elements must have an explicit `type` attribute.
• `checked` should be used with either `onChange` or…

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/47bc8b95ce2cecfc. Report an issue: GitHub.

Appendix: source

Thrown at crates/oxc_linter/src/rules/react/jsx_no_duplicate_props.rs:18

use oxc_ast::{
    AstKind,
    ast::{JSXAttributeItem, JSXAttributeName},
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::Span;
use oxc_str::Str;
use rustc_hash::FxHashMap;

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

fn jsx_no_duplicate_props_diagnostic(prop_name: &str, span1: Span, span2: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn(format!(
        "No duplicate props allowed. The prop \"{prop_name}\" is duplicated."
    ))
    .with_help("Remove one of the props, or rename them so each prop is distinct.")
    .with_labels([span1, span2])
}

#[derive(Debug, Default, Clone)]
pub struct JsxNoDuplicateProps;

declare_oxc_lint!(
    /// ### What it does
    ///
    /// This rule prevents duplicate props in JSX elements.
    ///
    /// ### Why is this bad?
    ///
    /// Having duplicate props in a JSX element is most likely a mistake.
    /// Creating JSX elements with duplicate props can cause unexpected behavior in your application.

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