oxc-project/oxc · warning · OxcDiagnostic

this expression is assigned to itself

Error message

this expression is assigned to itself

What it means

oxlint's port of ESLint `no-self-assign`. It fires when both sides of an assignment are structurally the same target: `a = a`, `obj.a = obj.a` (with `props: true`, the default), and equivalent destructuring/array forms. Self-assignment has no effect (unless a proxy/setter is involved) and almost always indicates a typo or unfinished refactor.

Source

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

        AssignmentTargetProperty, Expression, MemberExpression, ObjectProperty, ObjectPropertyKind,
        SimpleAssignmentTarget, match_assignment_target, match_simple_assignment_target,
    },
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::{GetSpan, Span};
use oxc_syntax::operator::AssignmentOperator;
use schemars::JsonSchema;
use serde::Deserialize;

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

fn no_self_assign_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("this expression is assigned to itself")
        .with_help("Remove the self-assignment or assign to a different variable.")
        .with_label(span)
}

#[derive(Debug, Clone, Deserialize, JsonSchema)]
#[serde(rename_all = "camelCase", default, deny_unknown_fields)]
pub struct NoSelfAssign {
    /// The `props` option when set to `false`, disables the checking of properties.
    ///
    /// With `props` set to `false` the following are examples of correct code:
    /// ```javascript
    /// obj.a = obj.a;
    /// obj.a.b = obj.a.b;
    /// obj["a"] = obj["a"];
    /// obj[a] = obj[a];
    /// ```
    props: bool,
}

View on GitHub (pinned to e1e7af627c)

Solutions

1. Delete the self-assignment statement.
2. Fix the intended right-hand side (`obj.a = obj.b;`).
3. If you truly need to invoke a setter, call an explicit method or use `void obj.a;` reading the property, and suppress with an `oxlint-ignore no-self-assign` comment.
4. Set `"props": false` when property self-assignment must be allowed wholesale.

Example fix

// before
obj.a = obj.a;

// after
obj.a = obj.b;

// AST-free heuristic for self-assignment lines
function selfAssignments(src) {
  return [...src.matchAll(/^\s*([\w$.]+)\s*=\s*\1\s*;?\s*$/gm)].map(m => m[0]);
}

When it happens

Trigger: `a = a;`, `this.x = this.x;`, `obj.a = obj.a` with default `props: true`; setting `"props": false` limits the check to plain identifiers. Array patterns like `[a] = [a];` are also covered.

Common situations: Rename refactors that missed one side; copy-paste of `x = y` lines; the rare intentional case of triggering a setter via `el.checked = el.checked`.

Related errors

• Both sides of this comparison are exactly the same
• Setter cannot return a value
• Empty array binding pattern
• Empty object binding pattern
• `debugger` statement is not allowed

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/88a0433832a6040a. Report an issue: GitHub.