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therewillbecodetherewillbecode
authoredMar 13, 2025··
feat(linter): Add eslint/no-lonely-if (#9660)
Relates to #479 . Rule details: https://eslint.org/docs/latest/rules/no-lonely-if
·
oxlint_v0.16.3crates_v0.59.0
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‎crates/oxc_linter/src/rules.rs

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@@ -104,6 +104,7 @@ mod eslint {
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pub mod no_label_var;
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pub mod no_labels;
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pub mod no_lone_blocks;
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pub mod no_lonely_if;
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pub mod no_loss_of_precision;
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pub mod no_magic_numbers;
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pub mod no_multi_assign;
@@ -577,6 +578,7 @@ oxc_macros::declare_all_lint_rules! {
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eslint::max_lines,
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eslint::max_params,
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eslint::new_cap,
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eslint::no_lonely_if,
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eslint::no_useless_call,
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eslint::no_unneeded_ternary,
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eslint::no_extra_label,

‎crates/oxc_linter/src/rules/eslint/no_lonely_if.rs

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@@ -0,0 +1,290 @@
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use crate::{AstNode, context::LintContext, rule::Rule};
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use oxc_ast::AstKind;
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use oxc_ast::ast::{Statement, Statement::BlockStatement};
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use oxc_diagnostics::OxcDiagnostic;
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use oxc_macros::declare_oxc_lint;
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use oxc_span::Span;
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fn no_lonely_if_diagnostic(span: Span) -> OxcDiagnostic {
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OxcDiagnostic::warn("Unexpected `if` as the only statement in an `else` block")
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.with_help("Consider using `else if` instead.")
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.with_label(span)
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}
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#[derive(Debug, Default, Clone)]
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pub struct NoLonelyIf;
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declare_oxc_lint!(
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/// ### What it does
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///
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/// Disallow `if` statements as the only statement in `else` blocks
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///
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/// ### Why is this bad?
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///
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/// When an `if` statement is the only statement in an `else` block, it is often clearer to use
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/// an `else if` instead.
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///
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/// ### Examples
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///
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/// Examples of **incorrect** code for this rule:
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/// ```js
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/// if (condition) {
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/// // ...
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/// } else {
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/// if (anotherCondition) {
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/// // ...
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/// }
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/// }
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/// ```
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///
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/// ```js
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/// if (condition) {
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/// // ...
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/// } else {
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/// if (anotherCondition) {
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/// // ...
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/// } else {
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/// // ...
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/// }
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/// }
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/// ```
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///
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/// Examples of **correct** code for this rule:
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/// ```js
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/// if (condition) {
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/// // ...
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/// } else if (anotherCondition) {
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/// // ...
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/// }
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/// ```
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///
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/// ```js
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/// if (condition) {
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/// // ...
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/// } else if (anotherCondition) {
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/// // ...
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/// } else {
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/// // ...
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/// }
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/// ```
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///
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/// ```js
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/// if (condition) {
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/// // ...
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/// } else {
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/// if (anotherCondition) {
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/// // ...
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/// }
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/// doSomething();
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/// }
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/// ```
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NoLonelyIf,
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eslint,
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pedantic,
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pending
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);
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impl Rule for NoLonelyIf {
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fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
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let AstKind::IfStatement(if_stmt) = node.kind() else {
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return;
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};
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let Some(ref alternate) = if_stmt.alternate else {
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return;
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};
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let BlockStatement(b) = alternate else {
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return;
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};
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if b.body.len() != 1 {
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return;
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};
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let Some(only_stmt) = b.body.first() else {
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return;
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};
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if let Some(AstKind::IfStatement(_)) = ctx.nodes().parent_kind(node.id()) {
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return;
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};
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if let Statement::BlockStatement(inner_block) = only_stmt {
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if inner_block.body.len() == 1 {
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if let Some(Statement::IfStatement(lonely_if)) = inner_block.body.first() {
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ctx.diagnostic(no_lonely_if_diagnostic(Span::sized(lonely_if.span.start, 2)));
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};
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}
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} else if let Statement::IfStatement(lonely_if) = only_stmt {
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ctx.diagnostic(no_lonely_if_diagnostic(Span::sized(lonely_if.span.start, 2)));
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};
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}
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}
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#[test]
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fn test() {
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use crate::tester::Tester;
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let pass = vec![
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"if (a) {;} else if (b) {;}",
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"if (a) {;} else { if (b) {;} ; }",
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"if (a) if (a) {} else { if (b) {} } else {}",
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"if (a) {
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if (b) {} else { }
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} else {
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if (c) { }
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if (d) { }
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}",
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];
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let fail = vec![
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"if (a) {;} else { if (b) {;} }",
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"if (foo) {} else { if (bar) baz(); }",
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"if (foo) {} else { if (bar) baz() } qux();",
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"if (foo) {} else { if (bar) baz(); } qux();",
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"if (a) {
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foo();
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} else {
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/* otherwise, do the other thing */ if (b) {
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bar();
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}
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}",
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"if (a) {
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foo();
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} else {
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if (b) {
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bar();
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} /* this comment will prevent this test case from being autofixed. */
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}",
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// No fix; removing the braces would cause a SyntaxError.
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"if (foo) {
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} else {
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if (bar) baz();
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}
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qux();",
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// Not fixed; removing the braces would change the semantics due to ASI.
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"if (foo) {
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} else {
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if (bar) baz();
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}
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[1, 2, 3].forEach(foo);",
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// Not fixed; removing the braces would change the semantics due to ASI.
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"if (foo) { } else {
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if (bar) baz++;
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}
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foo;",
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// Not fixed; bar() would be interpreted as a template literal tag
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"if (a) {
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foo();
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} else {
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if (b) bar();
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}
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`template literal`;",
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];
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/* Pending
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let fix = vec![
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(
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"if (a) {
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foo();
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} else {
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if (b) {
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bar();
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}
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}",
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"if (a) {
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foo();
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} else if (b) {
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bar();
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}",
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None,
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),
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(
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"if (a) {
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foo();
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} /* comment */
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else {
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if (b) {
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bar();
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}
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}",
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"if (a) {
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foo();
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} /* comment */
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else {
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if (b) {
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bar();
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}
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}",
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None,
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),
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(
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"if (a) {
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foo();
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} else {
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if ( /* this comment is ok */
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b) {
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bar();
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}
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}",
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"if (a) {
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foo();
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} else if ( /* this comment is ok */
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b) {
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bar();
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}",
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None,
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),
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(
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"if (foo) {} else { if (bar) baz(); }",
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"if (foo) {} else if (bar) baz();",
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None,
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),
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(
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"if (foo) { } else { if (bar) baz(); } qux();",
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"if (foo) { } else if (bar) baz(); qux();",
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None,
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),
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(
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"if (foo) { } else { if (bar) baz++; } foo;",
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"if (foo) { } else if (bar) baz++; foo;",
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None,
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),
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(
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"if (a) {
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foo();
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} else {
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if (b) {
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bar();
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} else if (c) {
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baz();
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} else {
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qux();
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}
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}",
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"if (a) {
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foo();
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} else if (b) {
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bar();
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} else if (c) {
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baz();
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} else {
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qux();
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}",
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None,
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),
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("if (a) {;} else { if (b) {;} }", "if (a) {;} else if (b) {;}", None),
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("if (foo) {} else { if (bar) baz(); }", "if (foo) {} else if (bar) baz();", None),
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(
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"if (foo) {} else { if (bar) baz(); } qux();",
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"if (foo) {} else if (bar) baz(); qux();",
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None,
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),
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];
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*/
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Tester::new(NoLonelyIf::NAME, NoLonelyIf::PLUGIN, pass, fail)
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// .expect_fix(fix)
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.test_and_snapshot();
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}

‎crates/oxc_linter/src/snapshots/eslint_no_lonely_if.snap

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1+
---
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source: crates/oxc_linter/src/tester.rs
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---
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⚠ eslint(no-lonely-if): Unexpected `if` as the only statement in an `else` block
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╭─[no_lonely_if.tsx:1:19]
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1 │ if (a) {;} else { if (b) {;} }
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· ──
8+
╰────
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help: Consider using `else if` instead.
10+
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⚠ eslint(no-lonely-if): Unexpected `if` as the only statement in an `else` block
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╭─[no_lonely_if.tsx:1:20]
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1 │ if (foo) {} else { if (bar) baz(); }
14+
· ──
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╰────
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help: Consider using `else if` instead.
17+
18+
⚠ eslint(no-lonely-if): Unexpected `if` as the only statement in an `else` block
19+
╭─[no_lonely_if.tsx:1:20]
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1 │ if (foo) {} else { if (bar) baz() } qux();
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· ──
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╰────
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help: Consider using `else if` instead.
24+
25+
⚠ eslint(no-lonely-if): Unexpected `if` as the only statement in an `else` block
26+
╭─[no_lonely_if.tsx:1:20]
27+
1 │ if (foo) {} else { if (bar) baz(); } qux();
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· ──
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╰────
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help: Consider using `else if` instead.
31+
32+
⚠ eslint(no-lonely-if): Unexpected `if` as the only statement in an `else` block
33+
╭─[no_lonely_if.tsx:4:48]
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3 │ } else {
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4 │ /* otherwise, do the other thing */ if (b) {
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· ──
37+
5 │ bar();
38+
╰────
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help: Consider using `else if` instead.
40+
41+
⚠ eslint(no-lonely-if): Unexpected `if` as the only statement in an `else` block
42+
╭─[no_lonely_if.tsx:4:12]
43+
3 │ } else {
44+
4 │ if (b) {
45+
· ──
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5 │ bar();
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╰────
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help: Consider using `else if` instead.
49+
50+
⚠ eslint(no-lonely-if): Unexpected `if` as the only statement in an `else` block
51+
╭─[no_lonely_if.tsx:3:12]
52+
2 │ } else {
53+
3 │ if (bar) baz();
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· ──
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4 │ }
56+
╰────
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help: Consider using `else if` instead.
58+
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⚠ eslint(no-lonely-if): Unexpected `if` as the only statement in an `else` block
60+
╭─[no_lonely_if.tsx:3:12]
61+
2 │ } else {
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3 │ if (bar) baz();
63+
· ──
64+
4 │ }
65+
╰────
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help: Consider using `else if` instead.
67+
68+
⚠ eslint(no-lonely-if): Unexpected `if` as the only statement in an `else` block
69+
╭─[no_lonely_if.tsx:2:12]
70+
1 │ if (foo) { } else {
71+
2 │ if (bar) baz++;
72+
· ──
73+
3 │ }
74+
╰────
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help: Consider using `else if` instead.
76+
77+
⚠ eslint(no-lonely-if): Unexpected `if` as the only statement in an `else` block
78+
╭─[no_lonely_if.tsx:4:12]
79+
3 │ } else {
80+
4 │ if (b) bar();
81+
· ──
82+
5 │ }
83+
╰────
84+
help: Consider using `else if` instead.

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