What causes "Unexpected `if` as the only statement in an `else` block" in oxc-project/oxc?

Merge into an else-if chain: 'if (a) {...} else if (b) {...}'

oxc-project/oxc · warning · OxcDiagnostic

Unexpected `if` as the only statement in an `else` block

Error message

Unexpected `if` as the only statement in an `else` block

What it means

Diagnostic from oxlint's eslint/no-lonely-if rule (crates/oxc_linter/src/rules/eslint/no_lonely_if.rs:10). It reports an if statement that is the only statement inside an else block: 'if (a) {...} else { if (b) {...} }'. The idiomatic form is 'else if', which avoids the extra indentation and brace level. The label is placed on the span of the lonely if keyword.

Solutions

Merge into an else-if chain: 'if (a) {...} else if (b) {...}'
If the nested if has its own else, flatten the whole chain with else-if at each level
When the chain grows long, consider a lookup table, switch, or early-return guard clauses instead

Example fix

// before
if (a) {
  doA();
} else {
  if (b) {
    doB();
  }
}

// after
if (a) {
  doA();
} else if (b) {
  doB();
}

Defensive patterns

Strategy: validation

Prevention

When adding a condition to an if/else chain, append 'else if' instead of nesting inside the else block
Prefer guard clauses/early return over growing else chains
Enable no-lonely-if in the shared config so reviewers see it automatically

When it happens

Trigger: An else clause whose block contains exactly one statement and that statement is an if (with or without its own else chain); commonly produced when adding a new condition to an existing if/else by hand.

Common situations: Incrementally grown conditionals during bug fixes; code formatted with the else block always braced; developers unaware that 'else if' is just else followed by an if statement.

Related errors

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/0f87b44d5a1c750f. Report an issue: GitHub.

Appendix: source

Thrown at crates/oxc_linter/src/rules/eslint/no_lonely_if.rs:10

use crate::{AstNode, context::LintContext, rule::Rule};
use oxc_ast::AstKind;
use oxc_ast::ast::{IfStatement, Statement};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::Span;

fn no_lonely_if_diagnostic(lonely_if: &IfStatement) -> OxcDiagnostic {
    let span = Span::sized(lonely_if.span.start, 2);
    OxcDiagnostic::warn("Unexpected `if` as the only statement in an `else` block")
        .with_help("Consider using `else if` instead.")
        .with_label(span)
}

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

declare_oxc_lint!(
    /// ### What it does
    ///
    /// Disallow `if` statements as the only statement in `else` blocks.
    ///
    /// ### Why is this bad?
    ///
    /// When an `if` statement is the only statement in an `else` block, it is often clearer to use
    /// an `else if` instead.
    ///
    /// ### Examples

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