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feat(linter): eslint-plugin-unicorn/no-nested-ternary (#1417)
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This PR implements the
[eslint-plugin-unicorn/no-nested-ternary](https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/docs/rules/no-nested-ternary.md)
rule.

Tests taken from
https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/test/no-nested-ternary.mjs.

Related issue: #684
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@haocheng6
haocheng6 committed Nov 19, 2023
1 parent b72f83b commit 5543e8c
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2 changes: 2 additions & 0 deletions crates/oxc_linter/src/rules.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -159,6 +159,7 @@ mod unicorn {
pub mod no_invalid_remove_event_listener;
pub mod no_lonely_if;
pub mod no_negated_condition;
pub mod no_nested_ternary;
pub mod no_new_array;
pub mod no_new_buffer;
pub mod no_object_as_default_parameter;
Expand Down Expand Up @@ -317,6 +318,7 @@ oxc_macros::declare_all_lint_rules! {
unicorn::no_invalid_remove_event_listener,
unicorn::no_lonely_if,
unicorn::no_negated_condition,
unicorn::no_nested_ternary,
unicorn::no_new_array,
unicorn::no_new_buffer,
unicorn::no_object_as_default_parameter,
Expand Down
186 changes: 186 additions & 0 deletions crates/oxc_linter/src/rules/unicorn/no_nested_ternary.rs
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@@ -0,0 +1,186 @@
use oxc_ast::{ast::Expression, AstKind};
use oxc_diagnostics::{
miette::{self, Diagnostic},
thiserror::Error,
};
use oxc_macros::declare_oxc_lint;
use oxc_span::Span;

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

#[derive(Debug, Error, Diagnostic)]
enum NoNestedTernaryDiagnostic {
#[error("eslint-plugin-unicorn(no-nested-ternary): Unexpected nested ternary expression without parentheses.")]
#[diagnostic(severity(warning), help("Add parentheses around the nested ternary expression."))]
UnparenthesizedNestedTernary(#[label] Span),
#[error(
"eslint-plugin-unicorn(no-nested-ternary): Unexpected deeply nested ternary expression."
)]
#[diagnostic(
severity(warning),
help("Avoid nesting ternary expressions for more than one level.")
)]
DeeplyNestedTernary(#[label] Span),
}

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

declare_oxc_lint!(
/// ### What it does
/// This rule disallows deeply nested ternary expressions.
/// Nested ternary expressions that are only one level deep and wrapped in parentheses are allowed.
///
/// ### Why is this bad?
/// Nesting ternary expressions can make code more difficult to understand.
///
/// ### Example
/// ```javascript
/// // Fail
/// const foo = i > 5 ? i < 100 ? true : false : true;
/// const foo = i > 5 ? true : (i < 100 ? true : (i < 1000 ? true : false));
///
/// // Pass
/// const foo = i > 5 ? (i < 100 ? true : false) : true;
/// const foo = i > 5 ? (i < 100 ? true : false) : (i < 100 ? true : false);
/// ```
NoNestedTernary,
restriction
);

impl Rule for NoNestedTernary {
fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
let AstKind::ConditionalExpression(cond_expr) = node.kind() else { return };

if matches!(&cond_expr.test.get_inner_expression(), Expression::ConditionalExpression(_))
|| matches!(
&cond_expr.consequent.get_inner_expression(),
Expression::ConditionalExpression(_)
)
|| matches!(
&cond_expr.alternate.get_inner_expression(),
Expression::ConditionalExpression(_)
)
{
return;
}

let mut nested_level = 0;
let mut current_node = node;
while let Some(parent_node) = ctx.nodes().parent_node(current_node.id()) {
match parent_node.kind() {
AstKind::ConditionalExpression(_) => {
nested_level += 1;
}
AstKind::ParenthesizedExpression(_) => {}
_ => break,
}
if nested_level == 2 {
break;
}
current_node = parent_node;
}

match nested_level {
0 => {}
1 => {
let Some(parent_node) = ctx.nodes().parent_node(node.id()) else { unreachable!() };
if let AstKind::ParenthesizedExpression(_) = parent_node.kind() {
return;
}
ctx.diagnostic_with_fix(
NoNestedTernaryDiagnostic::UnparenthesizedNestedTernary(cond_expr.span),
|| {
Fix::new(
format!("({})", cond_expr.span.source_text(ctx.source_text())),
cond_expr.span,
)
},
);
}
2 => {
ctx.diagnostic(NoNestedTernaryDiagnostic::DeeplyNestedTernary(cond_expr.span));
}
_ => unreachable!(),
}
}
}

#[test]
fn test() {
use crate::tester::Tester;

let pass = vec![
r"const foo = i > 5 ? true : false;",
r"const foo = i > 5 ? true : (i < 100 ? true : false);",
r"const foo = i > 5 ? (i < 100 ? true : false) : true;",
r"const foo = i > 5 ? (i < 100 ? true : false) : (i < 100 ? true : false);",
r"const foo = i > 5 ? true : (i < 100 ? FOO(i > 50 ? false : true) : false);",
r"foo ? doBar() : doBaz();",
r"var foo = bar === baz ? qux : quxx;",
r"
const pluginName = isAbsolute ?
pluginPath.slice(pluginPath.lastIndexOf('/') + 1) :
(
isNamespaced ?
pluginPath.split('@')[1].split('/')[1] :
pluginPath
);
",
];

let fail = vec![
r"const foo = i > 5 ? true : (i < 100 ? true : (i < 1000 ? true : false));",
r"const foo = i > 5 ? true : (i < 100 ? (i > 50 ? false : true) : false);",
r"const foo = i > 5 ? i < 100 ? true : false : true;",
r"const foo = i > 5 ? i < 100 ? true : false : i < 100 ? true : false;",
r"const foo = i > 5 ? true : i < 100 ? true : false;",
r"foo ? bar : baz === qux ? quxx : foobar;",
r"foo ? baz === qux ? quxx : foobar : bar;",
r"
const foo = a ?
b :
(
c ?
d :
(
e ?
f :
(g ? h : i)
)
)
",
];

let fix = vec![
(
"const foo = i > 5 ? i < 100 ? true : false : true;",
"const foo = i > 5 ? (i < 100 ? true : false) : true;",
None,
),
(
"const foo = i > 5 ? i < 100 ? true : false : i < 100 ? true : false;",
"const foo = i > 5 ? (i < 100 ? true : false) : (i < 100 ? true : false);",
None,
),
(
"const foo = i > 5 ? true : i < 100 ? true : false;",
"const foo = i > 5 ? true : (i < 100 ? true : false);",
None,
),
(
"foo ? bar : baz === qux ? quxx : foobar;",
"foo ? bar : (baz === qux ? quxx : foobar);",
None,
),
(
"foo ? baz === qux ? quxx : foobar : bar;",
"foo ? (baz === qux ? quxx : foobar) : bar;",
None,
),
];

Tester::new_without_config(NoNestedTernary::NAME, pass, fail)
.expect_fix(fix)
.test_and_snapshot();
}
70 changes: 70 additions & 0 deletions crates/oxc_linter/src/snapshots/no_nested_ternary.snap
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---
source: crates/oxc_linter/src/tester.rs
expression: no_nested_ternary
---
⚠ eslint-plugin-unicorn(no-nested-ternary): Unexpected deeply nested ternary expression.
╭─[no_nested_ternary.tsx:1:1]
1 │ const foo = i > 5 ? true : (i < 100 ? true : (i < 1000 ? true : false));
· ───────────────────────
╰────
help: Avoid nesting ternary expressions for more than one level.

⚠ eslint-plugin-unicorn(no-nested-ternary): Unexpected deeply nested ternary expression.
╭─[no_nested_ternary.tsx:1:1]
1 │ const foo = i > 5 ? true : (i < 100 ? (i > 50 ? false : true) : false);
· ─────────────────────
╰────
help: Avoid nesting ternary expressions for more than one level.

⚠ eslint-plugin-unicorn(no-nested-ternary): Unexpected nested ternary expression without parentheses.
╭─[no_nested_ternary.tsx:1:1]
1 │ const foo = i > 5 ? i < 100 ? true : false : true;
· ──────────────────────
╰────
help: Add parentheses around the nested ternary expression.

⚠ eslint-plugin-unicorn(no-nested-ternary): Unexpected nested ternary expression without parentheses.
╭─[no_nested_ternary.tsx:1:1]
1 │ const foo = i > 5 ? i < 100 ? true : false : i < 100 ? true : false;
· ──────────────────────
╰────
help: Add parentheses around the nested ternary expression.

⚠ eslint-plugin-unicorn(no-nested-ternary): Unexpected nested ternary expression without parentheses.
╭─[no_nested_ternary.tsx:1:1]
1 │ const foo = i > 5 ? i < 100 ? true : false : i < 100 ? true : false;
· ──────────────────────
╰────
help: Add parentheses around the nested ternary expression.

⚠ eslint-plugin-unicorn(no-nested-ternary): Unexpected nested ternary expression without parentheses.
╭─[no_nested_ternary.tsx:1:1]
1 │ const foo = i > 5 ? true : i < 100 ? true : false;
· ──────────────────────
╰────
help: Add parentheses around the nested ternary expression.

⚠ eslint-plugin-unicorn(no-nested-ternary): Unexpected nested ternary expression without parentheses.
╭─[no_nested_ternary.tsx:1:1]
1 │ foo ? bar : baz === qux ? quxx : foobar;
· ───────────────────────────
╰────
help: Add parentheses around the nested ternary expression.

⚠ eslint-plugin-unicorn(no-nested-ternary): Unexpected nested ternary expression without parentheses.
╭─[no_nested_ternary.tsx:1:1]
1 │ foo ? baz === qux ? quxx : foobar : bar;
· ───────────────────────────
╰────
help: Add parentheses around the nested ternary expression.

⚠ eslint-plugin-unicorn(no-nested-ternary): Unexpected deeply nested ternary expression.
╭─[no_nested_ternary.tsx:9:1]
9 │ f :
10 │ (g ? h : i)
· ─────────
11 │ )
╰────
help: Avoid nesting ternary expressions for more than one level.


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