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feat(linter): @typescript-eslint/prefer-for-of (#2789)

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2
crates/oxc_linter/src/rules.rs
View file

@ -137,6 +137,7 @@ mod typescript {
pub mod no_unsafe_declaration_merging;
pub mod no_var_requires;
pub mod prefer_as_const;
pub mod prefer_for_of;
pub mod prefer_function_type;
pub mod prefer_ts_expect_error;
pub mod triple_slash_reference;
@ -469,6 +470,7 @@ oxc_macros::declare_all_lint_rules! {
typescript::no_unsafe_declaration_merging,
typescript::no_var_requires,
typescript::prefer_as_const,
typescript::prefer_for_of,
typescript::prefer_function_type,
typescript::prefer_ts_expect_error,
typescript::triple_slash_reference,

291
crates/oxc_linter/src/rules/typescript/prefer_for_of.rs Normal file
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@ -0,0 +1,291 @@
use oxc_ast::ast::{
AssignmentTarget, BindingPatternKind, Expression, ForStatementInit, SimpleAssignmentTarget,
VariableDeclarationKind,
};
use oxc_ast::AstKind;
use oxc_diagnostics::{
miette::{self, Diagnostic},
thiserror::Error,
};
use oxc_macros::declare_oxc_lint;
use oxc_span::{Atom, GetSpan, Span};
use oxc_syntax::operator::{AssignmentOperator, BinaryOperator, UnaryOperator, UpdateOperator};
use crate::{context::LintContext, rule::Rule, AstNode};
#[derive(Debug, Error, Diagnostic)]
#[error("typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.")]
#[diagnostic(severity(warning), help("Consider using a for-of loop for this simple iteration."))]
struct PreferForOfDiagnostic(#[label] pub Span);
#[derive(Debug, Default, Clone)]
pub struct PreferForOf;
declare_oxc_lint!(
/// ### What it does
/// Enforces the use of for-of loop instead of a for loop with a simple iteration.
///
/// ### Why is this bad?
/// Using a for loop with a simple iteration over an array can be replaced with a more concise
/// and readable for-of loop. For-of loops are easier to read and less error-prone, as they
/// eliminate the need for an index variable and manual array access.
///
/// ### Example
/// ```javascript
/// // Bad
/// for (let i = 0; i < arr.length; i++) {
/// console.log(arr[i]);
/// }
///
/// // Good
/// for (const item of arr) {
/// console.log(item);
/// }
/// ```
PreferForOf,
style
);
trait SpanExt {
fn contains(&self, other: Self) -> bool;
}
impl SpanExt for Span {
fn contains(&self, other: Self) -> bool {
self.start <= other.start && self.end >= other.end
}
}
trait ExpressionExt {
fn is_increment_of(&self, var_name: &Atom) -> bool;
}
impl<'a> ExpressionExt for Expression<'a> {
fn is_increment_of(&self, var_name: &Atom) -> bool {
match self {
Expression::UpdateExpression(expr) => match (&expr.argument, &expr.operator) {
(
SimpleAssignmentTarget::AssignmentTargetIdentifier(id),
UpdateOperator::Increment,
) => id.name == var_name,
_ => false,
},
Expression::AssignmentExpression(expr) => {
if !matches!(&expr.left,
AssignmentTarget::SimpleAssignmentTarget(
SimpleAssignmentTarget::AssignmentTargetIdentifier(id)
)
if id.name == var_name
) {
return false;
}
match expr.operator {
AssignmentOperator::Addition => {
matches!(&expr.right, Expression::NumericLiteral(lit)
if (lit.value - 1f64).abs() < f64::EPSILON)
}
AssignmentOperator::Assign => {
let Expression::BinaryExpression(bin_expr) = &expr.right else {
return false;
};
if bin_expr.operator != BinaryOperator::Addition {
return false;
}
match (&bin_expr.left, &bin_expr.right) {
(Expression::Identifier(id), Expression::NumericLiteral(lit))
| (Expression::NumericLiteral(lit), Expression::Identifier(id)) => {
id.name == var_name && (lit.value - 1f64).abs() < f64::EPSILON
}
_ => false,
}
}
_ => false,
}
}
_ => false,
}
}
}
impl Rule for PreferForOf {
fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
let AstKind::ForStatement(for_stmt) = node.kind() else { return };
let Some(ForStatementInit::VariableDeclaration(for_stmt_init)) = &for_stmt.init else {
return;
};
if for_stmt_init.declarations.len() != 1
|| for_stmt_init.kind == VariableDeclarationKind::Const
{
return;
}
let decl = &for_stmt_init.declarations[0];
let (var_name, var_symbol_id) = match &decl.id.kind {
BindingPatternKind::BindingIdentifier(id) => (&id.name, id.symbol_id.get()),
_ => return,
};
if !matches!(&decl.init,
Some(Expression::NumericLiteral(literal)) if literal.value == 0f64
) {
return;
}
let Some(Expression::BinaryExpression(test_expr)) = &for_stmt.test else { return };
if !matches!((&test_expr.left, test_expr.operator),
(Expression::Identifier(id), BinaryOperator::LessThan) if id.name == var_name
) {
return;
}
let array_name = {
let Expression::MemberExpression(mem_expr) = &test_expr.right else { return };
if !matches!(mem_expr.static_property_name(), Some(prop_name) if prop_name == "length")
{
return;
}
match &mem_expr.object() {
Expression::Identifier(id) => id.name.as_str(),
Expression::MemberExpression(mem_expr) => match mem_expr.static_property_name() {
Some(array_name) => array_name,
None => return,
},
_ => return,
}
};
let Some(update_expr) = &for_stmt.update else { return };
if !update_expr.is_increment_of(var_name) {
return;
}
let nodes = ctx.nodes();
let body_span = for_stmt.body.span();
let Some(var_symbol_id) = var_symbol_id else { return };
if ctx.semantic().symbol_references(var_symbol_id).any(|reference| {
let ref_id = reference.node_id();
let symbol_span = nodes.get_node(ref_id).kind().span();
if !body_span.contains(symbol_span) {
return false;
}
let Some(ref_parent) = nodes.parent_node(ref_id) else { return true };
if let Some(ref_grand_parent) = nodes.parent_node(ref_parent.id()) {
match ref_grand_parent.kind() {
AstKind::SimpleAssignmentTarget(_) => {
return true;
}
AstKind::UnaryExpression(unary_expr)
if unary_expr.operator == UnaryOperator::Delete =>
{
return true;
}
_ => {}
}
}
let parent_kind = ref_parent.kind();
let AstKind::MemberExpression(mem_expr) = parent_kind else { return true };
match mem_expr.object() {
Expression::Identifier(id) => id.name.as_str() != array_name,
Expression::MemberExpression(mem_expr) => match mem_expr.static_property_name() {
Some(prop_name) => prop_name != array_name,
None => true,
},
_ => true,
}
}) {
return;
}
let span = for_stmt_init.span.merge(&test_expr.span).merge(&update_expr.span());
ctx.diagnostic(PreferForOfDiagnostic(span));
}
}
#[test]
fn test() {
use crate::tester::Tester;
let pass = vec![
"for (let i = 0; i < arr1.length; i++) { const x = arr1[i] === arr2[i]; }",
"for (let i = 0; i < arr.length; i++) { arr[i] = 0; }",
"for (var c = 0; c < arr.length; c++) { doMath(c); }",
"for (var d = 0; d < arr.length; d++) doMath(d);",
"for (var e = 0; e < arr.length; e++) { if (e > 5) { doMath(e); } console.log(arr[e]); }",
"for (var f = 0; f <= 40; f++) { doMath(f); }",
"for (var g = 0; g <= 40; g++) doMath(g);",
"for (var h = 0, len = arr.length; h < len; h++) {}",
"for (var i = 0, len = arr.length; i < len; i++) arr[i];",
"var m = 0; for (;;) { if (m > 3) break; console.log(m); m++; }",
"var n = 0; for (; n < 9; n++) { console.log(n); }",
"var o = 0; for (; o < arr.length; o++) { console.log(arr[o]); }",
"for (; x < arr.length; x++) {}",
"for (let x = 0; ; x++) {}",
"for (let x = 0; x < arr.length; ) {}",
"for (let x = 0; NOTX < arr.length; x++) {}",
"for (let x = 0; x < arr.length; NOTX++) {}",
"for (let NOTX = 0; x < arr.length; x++) {}",
"for (let x = 0; x < arr.length; x--) {}",
"for (let x = 0; x <= arr.length; x++) {}",
"for (let x = 1; x < arr.length; x++) {}",
"for (let x = 0; x < arr.length(); x++) {}",
"for (let x = 0; x < arr.length; x += 11) {}",
"for (let x = arr.length; x > 1; x -= 1) {}",
"for (let x = 0; x < arr.length; x *= 2) {}",
"for (let x = 0; x < arr.length; x = x + 11) {}",
"for (let x = 0; x < arr.length; x++) { x++; }",
"for (let x = 0; true; x++) {}",
"for (var q in obj) { if (obj.hasOwnProperty(q)) { console.log(q); } }",
"for (var r of arr) { console.log(r); }",
"for (let x = 0; x < arr.length; x++) { let y = arr[x + 1]; }",
"for (let i = 0; i < arr.length; i++) { delete arr[i]; }",
"for (let i = 0; i < arr.length; i++) { [arr[i]] = [1]; }",
"for (let i = 0; i < arr.length; i++) { [...arr[i]] = [1]; }",
"for (let i = 0; i < arr1?.length; i++) { const x = arr1[i] === arr2[i]; }",
"for (let i = 0; i < arr?.length; i++) { arr[i] = 0; }",
"for (var c = 0; c < arr?.length; c++) { doMath(c); }",
"for (var d = 0; d < arr?.length; d++) doMath(d);",
"for (var c = 0; c < arr.length; c++) { doMath?.(c); }",
"for (var d = 0; d < arr.length; d++) doMath?.(d);",
"for (let i = 0; i < test.length; ++i) { this[i]; }",
"for (let i = 0; i < arr.length; i++) { ({ foo: arr[i] } = { foo: 1 }); }",
"for (let i = 0; i < arr.length; i++) { arr[i]++; }",
"function* gen() { for (let i = 0; i < this.length; ++i) { yield this[i]; } }",
];
let fail = vec![
"for (var a = 0; a < obj.arr.length; a++) { console.log(obj.arr[a]); }",
"for (var b = 0; b < arr.length; b++) console.log(arr[b]);",
"for (let a = 0; a < arr.length; a++) { console.log(arr[a]); }",
"for (var b = 0; b < arr.length; b++) console?.log(arr[b]);",
"for (let a = 0; a < arr.length; a++) { console?.log(arr[a]); }",
"for (let a = 0; a < arr.length; ++a) { arr[a].whatever(); }",
"for (let x = 0; x < arr.length; x++) {}",
"for (let x = 0; x < arr.length; x += 1) {}",
"for (let x = 0; x < arr.length; x = x + 1) {}",
"for (let x = 0; x < arr.length; x = 1 + x) {}",
"for (let shadow = 0; shadow < arr.length; shadow++) {
for (let shadow = 0; shadow < arr.length; shadow++) {}
}",
"for (let i = 0; i < arr.length; i++) { obj[arr[i]] = 1; }",
"for (let i = 0; i < arr.length; i++) { delete obj[arr[i]]; }",
"for (let i = 0; i < arr.length; i++) { [obj[arr[i]]] = [1]; }",
"for (let i = 0; i < arr.length; i++) { [...obj[arr[i]]] = [1]; }",
"for (let i = 0; i < arr.length; i++) { ({ foo: obj[arr[i]] } = { foo: 1 }); }",
"for (let i = 0; i < this.item.length; ++i) { this.item[i]; }",
"function* gen() { for (let i = 0; i < this.array.length; ++i) { yield this.array[i]; } }",
];
Tester::new(PreferForOf::NAME, pass, fail).test_and_snapshot();
}

139
crates/oxc_linter/src/snapshots/prefer_for_of.snap Normal file
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@ -0,0 +1,139 @@
---
source: crates/oxc_linter/src/tester.rs
expression: prefer_for_of
---
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (var a = 0; a < obj.arr.length; a++) { console.log(obj.arr[a]); }
· ──────────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (var b = 0; b < arr.length; b++) console.log(arr[b]);
· ──────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let a = 0; a < arr.length; a++) { console.log(arr[a]); }
· ──────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (var b = 0; b < arr.length; b++) console?.log(arr[b]);
· ──────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let a = 0; a < arr.length; a++) { console?.log(arr[a]); }
· ──────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let a = 0; a < arr.length; ++a) { arr[a].whatever(); }
· ──────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let x = 0; x < arr.length; x++) {}
· ──────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let x = 0; x < arr.length; x += 1) {}
· ─────────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let x = 0; x < arr.length; x = x + 1) {}
· ────────────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let x = 0; x < arr.length; x = 1 + x) {}
· ────────────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let shadow = 0; shadow < arr.length; shadow++) {
· ─────────────────────────────────────────────
2 │ for (let shadow = 0; shadow < arr.length; shadow++) {}
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:2:18]
1 │ for (let shadow = 0; shadow < arr.length; shadow++) {
2 │ for (let shadow = 0; shadow < arr.length; shadow++) {}
· ─────────────────────────────────────────────
3 │ }
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let i = 0; i < arr.length; i++) { obj[arr[i]] = 1; }
· ──────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let i = 0; i < arr.length; i++) { delete obj[arr[i]]; }
· ──────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let i = 0; i < arr.length; i++) { [obj[arr[i]]] = [1]; }
· ──────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let i = 0; i < arr.length; i++) { [...obj[arr[i]]] = [1]; }
· ──────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let i = 0; i < arr.length; i++) { ({ foo: obj[arr[i]] } = { foo: 1 }); }
· ──────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:6]
1 │ for (let i = 0; i < this.item.length; ++i) { this.item[i]; }
· ────────────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.
⚠ typescript-eslint(prefer-for-of): Expected a `for-of` loop instead of a `for` loop with this simple iteration.
╭─[prefer_for_of.tsx:1:24]
1 │ function* gen() { for (let i = 0; i < this.array.length; ++i) { yield this.array[i]; } }
· ─────────────────────────────────────
╰────
help: Consider using a for-of loop for this simple iteration.