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Sep 19, 2025
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clean-up single_match a bit #15641

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27 changes: 15 additions & 12 deletions clippy_lints/src/matches/single_match.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,17 +24,16 @@ use super::{MATCH_BOOL, SINGLE_MATCH, SINGLE_MATCH_ELSE};
/// span, e.g. a string literal `"//"`, but we know that this isn't the case for empty
/// match arms.
fn empty_arm_has_comment(cx: &LateContext<'_>, span: Span) -> bool {
if let Some(ff) = span.get_source_range(cx)
&& let Some(text) = ff.as_str()
{
text.as_bytes().windows(2).any(|w| w == b"//" || w == b"/*")
} else {
false
}
span.check_source_text(cx, |text| text.as_bytes().windows(2).any(|w| w == b"//" || w == b"/*"))
}

#[rustfmt::skip]
pub(crate) fn check<'tcx>(cx: &LateContext<'tcx>, ex: &'tcx Expr<'_>, arms: &'tcx [Arm<'_>], expr: &'tcx Expr<'_>, contains_comments: bool) {
pub(crate) fn check<'tcx>(
cx: &LateContext<'tcx>,
ex: &'tcx Expr<'_>,
arms: &'tcx [Arm<'_>],
expr: &'tcx Expr<'_>,
contains_comments: bool,
) {
if let [arm1, arm2] = arms
&& !arms.iter().any(|arm| arm.guard.is_some() || arm.pat.span.from_expansion())
&& !expr.span.from_expansion()
Expand Down Expand Up @@ -226,13 +225,13 @@ enum PatState<'a> {
Wild,
/// A std enum we know won't be extended. Tracks the states of each variant separately.
///
/// This is not used for `Option` since it uses the current pattern to track it's state.
/// This is not used for `Option` since it uses the current pattern to track its state.
StdEnum(&'a mut [PatState<'a>]),
/// Either the initial state for a pattern or a non-std enum. There is currently no need to
/// distinguish these cases.
///
/// For non-std enums there's no need to track the state of sub-patterns as the state of just
/// this pattern on it's own is enough for linting. Consider two cases:
/// this pattern on its own is enough for linting. Consider two cases:
/// * This enum has no wild match. This case alone is enough to determine we can lint.
/// * This enum has a wild match and therefore all sub-patterns also have a wild match.
///
Expand Down Expand Up @@ -380,7 +379,11 @@ impl<'a> PatState<'a> {
self.add_pat(cx, pat)
},
PatKind::Tuple([sub_pat], pos)
if pos.as_opt_usize().is_none() || cx.typeck.pat_ty(pat).tuple_fields().len() == 1 =>
// `pat` looks like `(sub_pat)`, without a `..` -- has only one sub-pattern
if pos.as_opt_usize().is_none()
// `pat` looks like `(sub_pat, ..)` or `(.., sub_pat)`, but its type is a unary tuple,
// so it still only has one sub-pattern
|| cx.typeck.pat_ty(pat).tuple_fields().len() == 1 =>
{
self.add_pat(cx, sub_pat)
},
Expand Down
5 changes: 3 additions & 2 deletions tests/ui/single_match.fixed
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Expand Up @@ -218,7 +218,7 @@ fn main() {
};
}

fn issue_10808(bar: Option<i32>) {
fn issue10808(bar: Option<i32>) {
if let Some(v) = bar { unsafe {
let r = &v as *const i32;
println!("{}", *r);
Expand Down Expand Up @@ -330,6 +330,7 @@ pub struct Data([u8; 4]);
const DATA: Data = Data([1, 2, 3, 4]);
const CONST_I32: i32 = 1;

// https://github.com/rust-lang/rust-clippy/issues/13012
fn irrefutable_match() {
println!();
//~^^^^ single_match
Expand Down Expand Up @@ -367,7 +368,7 @@ fn irrefutable_match() {
//~| NOTE: you might want to preserve the comments from inside the `match`
}

fn issue_14493() {
fn issue14493() {
macro_rules! mac {
(some) => {
Some(42)
Expand Down
5 changes: 3 additions & 2 deletions tests/ui/single_match.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -269,7 +269,7 @@ fn main() {
};
}

fn issue_10808(bar: Option<i32>) {
fn issue10808(bar: Option<i32>) {
match bar {
Some(v) => unsafe {
let r = &v as *const i32;
Expand Down Expand Up @@ -397,6 +397,7 @@ pub struct Data([u8; 4]);
const DATA: Data = Data([1, 2, 3, 4]);
const CONST_I32: i32 = 1;

// https://github.com/rust-lang/rust-clippy/issues/13012
fn irrefutable_match() {
match DATA {
DATA => println!(),
Expand Down Expand Up @@ -462,7 +463,7 @@ fn irrefutable_match() {
//~| NOTE: you might want to preserve the comments from inside the `match`
}

fn issue_14493() {
fn issue14493() {
macro_rules! mac {
(some) => {
Some(42)
Expand Down
20 changes: 10 additions & 10 deletions tests/ui/single_match.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -225,7 +225,7 @@ LL | | }
| |_____^ help: try: `if &s[0..3] == b"foo" { println!() }`

error: this pattern is irrefutable, `match` is useless
--> tests/ui/single_match.rs:401:5
--> tests/ui/single_match.rs:402:5
|
LL | / match DATA {
LL | | DATA => println!(),
Expand All @@ -234,7 +234,7 @@ LL | | }
| |_____^ help: try: `println!();`

error: this pattern is irrefutable, `match` is useless
--> tests/ui/single_match.rs:407:5
--> tests/ui/single_match.rs:408:5
|
LL | / match CONST_I32 {
LL | | CONST_I32 => println!(),
Expand All @@ -243,7 +243,7 @@ LL | | }
| |_____^ help: try: `println!();`

error: this pattern is irrefutable, `match` is useless
--> tests/ui/single_match.rs:414:5
--> tests/ui/single_match.rs:415:5
|
LL | / match i {
LL | | i => {
Expand All @@ -263,7 +263,7 @@ LL + }
|

error: this pattern is irrefutable, `match` is useless
--> tests/ui/single_match.rs:423:5
--> tests/ui/single_match.rs:424:5
|
LL | / match i {
LL | | i => {},
Expand All @@ -272,7 +272,7 @@ LL | | }
| |_____^ help: `match` expression can be removed

error: this pattern is irrefutable, `match` is useless
--> tests/ui/single_match.rs:429:5
--> tests/ui/single_match.rs:430:5
|
LL | / match i {
LL | | i => (),
Expand All @@ -281,7 +281,7 @@ LL | | }
| |_____^ help: `match` expression can be removed

error: this pattern is irrefutable, `match` is useless
--> tests/ui/single_match.rs:435:5
--> tests/ui/single_match.rs:436:5
|
LL | / match CONST_I32 {
LL | | CONST_I32 => println!(),
Expand All @@ -290,7 +290,7 @@ LL | | }
| |_____^ help: try: `println!();`

error: you seem to be trying to use `match` for destructuring a single pattern. Consider using `if let`
--> tests/ui/single_match.rs:443:5
--> tests/ui/single_match.rs:444:5
|
LL | / match x.pop() {
LL | | // bla
Expand All @@ -302,7 +302,7 @@ LL | | }
= note: you might want to preserve the comments from inside the `match`

error: you seem to be trying to use `match` for destructuring a single pattern. Consider using `if let`
--> tests/ui/single_match.rs:452:5
--> tests/ui/single_match.rs:453:5
|
LL | / match x.pop() {
LL | | // bla
Expand All @@ -322,7 +322,7 @@ LL + }
|

error: you seem to be trying to use `match` for destructuring a single pattern. Consider using `if let`
--> tests/ui/single_match.rs:478:5
--> tests/ui/single_match.rs:479:5
|
LL | / match mac!(some) {
LL | | Some(u) => println!("{u}"),
Expand All @@ -331,7 +331,7 @@ LL | | }
| |_____^ help: try: `if let Some(u) = mac!(some) { println!("{u}") }`

error: you seem to be trying to use `match` for an equality check. Consider using `if`
--> tests/ui/single_match.rs:486:5
--> tests/ui/single_match.rs:487:5
|
LL | / match mac!(str) {
LL | | "foo" => println!("eq"),
Expand Down