oxc-project/oxc · error · OxcDiagnostic

constraining the generic type {generic_type:?} to {constrain

Error message

constraining the generic type {generic_type:?} to {constraint:?} does nothing and is unnecessary

What it means

Raised by typescript/no-unnecessary-type-constraint when a generic type parameter is constrained to its default implicit bound, e.g. <T extends any> or <T extends unknown>. The constraint adds no restriction.

Source

Thrown at crates/oxc_linter/src/rules/typescript/no_unnecessary_type_constraint.rs:21

    ast::{TSType, TSTypeParameter, TSTypeParameterDeclaration},
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::{FileExtension, Span};

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

fn no_unnecessary_type_constraint_diagnostic(
    generic_type: &str,
    constraint: &str,
    span: Span,
    constraint_span: Span,
) -> OxcDiagnostic {
    OxcDiagnostic::warn(format!(
        "constraining the generic type {generic_type:?} to {constraint:?} does nothing and is unnecessary"
    ))
    .with_help(format!("Remove the unnecessary {constraint:?} constraint"))
    .with_labels([span, constraint_span])
}

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

declare_oxc_lint!(
    /// ### What it does
    ///
    /// Disallow unnecessary constraints on generic types.
    ///
    /// ### Why is this bad?
    ///
    /// Generic type parameters (`<T>`) in TypeScript may be "constrained" with an `extends`
    /// keyword. When no `extends` is provided, type parameters default a constraint to `unknown`.

View on GitHub (pinned to e1e7af627c)

Solutions

1. Remove the `extends any`/`extends unknown` constraint from the type parameter.

When it happens

Trigger: Thrown at crates/oxc_linter/src/rules/typescript/no_unnecessary_type_constraint.rs:21 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/2f65e4f2e9765243. Report an issue: GitHub.