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feat(no-unnecessary-await): add no-unnecessary-await rule #1523

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feat(no-unnecessary-await): add no-unnecessary-await rule #1523

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2585942
feat(no-unnecessary-await): add `no-unnecessary-await` rule
bartlomieju Jun 29, 2026
51d4728
fix(no-unnecessary-await): do not flag awaited logical expressions
bartlomieju Jul 6, 2026
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2 changes: 2 additions & 0 deletions src/rules.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,7 @@ pub mod no_this_before_super;
pub mod no_throw_literal;
pub mod no_top_level_await;
pub mod no_undef;
pub mod no_unnecessary_await;
pub mod no_unreachable;
pub mod no_unsafe_finally;
pub mod no_unsafe_negation;
Expand Down Expand Up @@ -352,6 +353,7 @@ fn get_all_rules_raw() -> Vec<Box<dyn LintRule>> {
Box::new(no_throw_literal::NoThrowLiteral),
Box::new(no_top_level_await::NoTopLevelAwait),
Box::new(no_undef::NoUndef),
Box::new(no_unnecessary_await::NoUnnecessaryAwait),
Box::new(no_unreachable::NoUnreachable),
Box::new(no_unsafe_finally::NoUnsafeFinally),
Box::new(no_unsafe_negation::NoUnsafeNegation),
Expand Down
229 changes: 229 additions & 0 deletions src/rules/no_unnecessary_await.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,229 @@
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.

use super::{Context, LintRule};
use crate::handler::{Handler, Traverse};
use crate::tags::{self, Tags};
use crate::Program;
use deno_ast::swc::ast::BinaryOp;
use deno_ast::view::{AwaitExpr, Expr};
use deno_ast::SourceRanged;
use derive_more::Display;

#[derive(Debug)]
pub struct NoUnnecessaryAwait;

const CODE: &str = "no-unnecessary-await";

#[derive(Display)]
enum NoUnnecessaryAwaitMessage {
#[display(fmt = "Unexpected `await` on a non-Promise value")]
Unexpected,
}

#[derive(Display)]
enum NoUnnecessaryAwaitHint {
#[display(fmt = "Consider removing the `await`")]
Remove,
}

impl LintRule for NoUnnecessaryAwait {
fn tags(&self) -> Tags {
&[tags::RECOMMENDED]
}

fn code(&self) -> &'static str {
CODE
}

fn lint_program_with_ast_view<'view>(
&self,
context: &mut Context,
program: Program<'_>,
) {
NoUnnecessaryAwaitHandler.traverse(program, context);
}
}

struct NoUnnecessaryAwaitHandler;

impl Handler for NoUnnecessaryAwaitHandler {
fn await_expr(&mut self, await_expr: &AwaitExpr, ctx: &mut Context) {
if not_promise(&await_expr.arg) {
ctx.add_diagnostic_with_hint(
await_expr.range(),
CODE,
NoUnnecessaryAwaitMessage::Unexpected,
NoUnnecessaryAwaitHint::Remove,
);
}
}
}

/// Returns `true` for expressions that are definitely not thenables/promises,
/// mirroring oxc's `not_promise`.
fn not_promise(expr: &Expr) -> bool {
match expr {
Expr::Array(_)
| Expr::Arrow(_)
| Expr::Await(_)
| Expr::Class(_)
| Expr::Fn(_)
| Expr::JSXElement(_)
| Expr::JSXFragment(_)
| Expr::Lit(_)
| Expr::Tpl(_)
| Expr::Unary(_)
| Expr::Update(_) => true,
// Logical expressions (`&&`, `||`, `??`) are represented as `BinExpr` in
// the swc AST, but they can evaluate to a promise, so they are not
// guaranteed to be non-promises. Only non-logical binary expressions are.
Expr::Bin(bin) => !matches!(
bin.op(),
BinaryOp::LogicalOr | BinaryOp::LogicalAnd | BinaryOp::NullishCoalescing
),
Expr::Seq(seq) => seq.exprs.last().is_some_and(not_promise),
Expr::Paren(paren) => not_promise(&paren.expr),
_ => false,
}
}

#[cfg(test)]
mod tests {
use super::*;

// Some tests are derived from
// https://github.com/oxc-project/oxc/blob/main/crates/oxc_linter/src/rules/unicorn/no_unnecessary_await.rs
// MIT Licensed.

#[test]
fn no_unnecessary_await_valid() {
assert_lint_ok! {
NoUnnecessaryAwait,
"await {then}",
"await a ? b : c",
"await a || b",
"await a && b",
"await a ?? b",
"await (a || b)",
"await (a && b)",
"await (a ?? b)",
"await new Foo()",
"await tagged``",
"class A { async foo() { await this }}",
"async function * foo() {await (yield bar);}",
"await (1, Promise.resolve())",
};
}

#[test]
fn no_unnecessary_await_invalid() {
assert_lint_err! {
NoUnnecessaryAwait,
"await []": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await [Promise.resolve()]": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await (() => {})": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await (() => Promise.resolve())": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await (a === b)": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await (a instanceof Promise)": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await (a > b)": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await class {}": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await class extends Promise {}": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await function() {}": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await function name() {}": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await function() { return Promise.resolve() }": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await 0": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await 1": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await \"\"": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await \"string\"": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await true": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await false": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await null": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await 0n": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await 1n": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await `${Promise.resolve()}`": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await !Promise.resolve()": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await void Promise.resolve()": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await +Promise.resolve()": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await ~1": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await ++foo": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await foo--": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await (Promise.resolve(), 1)": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"async function foo() {+await +1}": [
{ col: 23, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"async function foo() {-await-1}": [
{ col: 23, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"async function foo() {+await -1}": [
{ col: 23, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"await await this.assertTotalDocumentCount(expectedFormattedTotalDocCount);": [
{ col: 0, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"async function foo() {+await ++a}": [
{ col: 23, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
],
"async function foo() {-await --a}": [
{ col: 23, message: NoUnnecessaryAwaitMessage::Unexpected, hint: NoUnnecessaryAwaitHint::Remove }
]
};
}
}