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Rollup merge of rust-lang#129103 - Nadrieril:dont-warn-empty-unreacha…
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…ble, r=compiler-errors

Don't warn empty branches unreachable for now

The [stabilization](rust-lang#122792) of `min_exhaustive_patterns` updated the `unreachable_pattern` lint to trigger on empty arms too. This has caused some amount of churn, and imposes an unjoyful `#[allow(unreachable_patterns)]` onto library authors who want to stay backwards-compatible.

While I think the lint should eventually cover these cases, for transition's sake I'd prefer to revert linting to what it was prior to stabilization, at least for now.

Fixes rust-lang#129031.

r? ``@compiler-errors``
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workingjubilee authored Sep 11, 2024
2 parents 8d6b88b + 5b7be14 commit 6879ee6
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6 changes: 5 additions & 1 deletion compiler/rustc_pattern_analysis/src/usefulness.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -951,7 +951,11 @@ impl<Cx: PatCx> PlaceInfo<Cx> {
self.is_scrutinee && matches!(ctors_for_ty, ConstructorSet::NoConstructors);
// Whether empty patterns are counted as useful or not. We only warn an empty arm unreachable if
// it is guaranteed unreachable by the opsem (i.e. if the place is `known_valid`).
let empty_arms_are_unreachable = self.validity.is_known_valid();
// We don't want to warn empty patterns as unreachable by default just yet. We will in a
// later version of rust or under a different lint name, see
// https://github.com/rust-lang/rust/pull/129103.
let empty_arms_are_unreachable = self.validity.is_known_valid()
&& (is_toplevel_exception || cx.is_exhaustive_patterns_feature_on());
// Whether empty patterns can be omitted for exhaustiveness. We ignore place validity in the
// toplevel exception and `exhaustive_patterns` cases for backwards compatibility.
let can_omit_empty_arms = self.validity.is_known_valid()
Expand Down
188 changes: 1 addition & 187 deletions tests/ui/pattern/usefulness/empty-types.never_pats.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -43,30 +43,6 @@ LL + _ => todo!(),
LL + }
|

error: unreachable pattern
--> $DIR/empty-types.rs:70:9
|
LL | (_, _) => {}
| ^^^^^^ matches no values because `(u32, !)` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:76:9
|
LL | _ => {}
| ^ matches no values because `(!, !)` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:79:9
|
LL | (_, _) => {}
| ^^^^^^ matches no values because `(!, !)` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:83:9
|
Expand Down Expand Up @@ -94,22 +70,6 @@ LL + Ok(_) => todo!(),
LL + }
|

error: unreachable pattern
--> $DIR/empty-types.rs:94:9
|
LL | Err(_) => {}
| ^^^^^^ matches no values because `!` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:99:9
|
LL | Err(_) => {}
| ^^^^^^ matches no values because `!` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error[E0004]: non-exhaustive patterns: `Ok(1_u32..=u32::MAX)` not covered
--> $DIR/empty-types.rs:96:11
|
Expand Down Expand Up @@ -156,54 +116,6 @@ help: you might want to use `let else` to handle the variant that isn't matched
LL | let Ok(_x) = &res_u32_never else { todo!() };
| ++++++++++++++++

error: unreachable pattern
--> $DIR/empty-types.rs:112:9
|
LL | _ => {}
| ^ matches no values because `Result<!, !>` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:115:9
|
LL | Ok(_) => {}
| ^^^^^ matches no values because `Result<!, !>` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:118:9
|
LL | Ok(_) => {}
| ^^^^^ matches no values because `Result<!, !>` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:119:9
|
LL | _ => {}
| ^ matches no values because `Result<!, !>` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:122:9
|
LL | Ok(_) => {}
| ^^^^^ matches no values because `Result<!, !>` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:123:9
|
LL | Err(_) => {}
| ^^^^^^ matches no values because `Result<!, !>` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:132:13
|
Expand All @@ -220,22 +132,6 @@ LL | _ if false => {}
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:143:13
|
LL | Some(_) => {}
| ^^^^^^^ matches no values because `Void` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:147:13
|
LL | None => {}
| ---- matches all the relevant values
LL | _ => {}
| ^ no value can reach this

error[E0004]: non-exhaustive patterns: `Some(!)` not covered
--> $DIR/empty-types.rs:156:15
|
Expand Down Expand Up @@ -303,30 +199,6 @@ LL | _ => {}
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:284:9
|
LL | (_, _) => {}
| ^^^^^^ matches no values because `(!, !)` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:287:9
|
LL | Ok(_) => {}
| ^^^^^ matches no values because `Result<!, !>` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:288:9
|
LL | Err(_) => {}
| ^^^^^^ matches no values because `Result<!, !>` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error[E0005]: refutable pattern in local binding
--> $DIR/empty-types.rs:297:13
|
Expand Down Expand Up @@ -474,30 +346,6 @@ LL + _ => todo!(),
LL + }
|

error: unreachable pattern
--> $DIR/empty-types.rs:368:9
|
LL | _ => {}
| ^ matches no values because `[!; 3]` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:371:9
|
LL | [_, _, _] => {}
| ^^^^^^^^^ matches no values because `[!; 3]` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:374:9
|
LL | [_, ..] => {}
| ^^^^^^^ matches no values because `[!; 3]` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error[E0004]: non-exhaustive patterns: type `[!; 0]` is non-empty
--> $DIR/empty-types.rs:388:11
|
Expand Down Expand Up @@ -534,40 +382,6 @@ LL ~ [..] if false => {},
LL + [] => todo!()
|

error: unreachable pattern
--> $DIR/empty-types.rs:416:9
|
LL | Some(_) => {}
| ^^^^^^^ matches no values because `!` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:421:9
|
LL | Some(_a) => {}
| ^^^^^^^^ matches no values because `!` is uninhabited
|
= note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types

error: unreachable pattern
--> $DIR/empty-types.rs:426:9
|
LL | None => {}
| ---- matches all the relevant values
LL | // !useful, !reachable
LL | _ => {}
| ^ no value can reach this

error: unreachable pattern
--> $DIR/empty-types.rs:431:9
|
LL | None => {}
| ---- matches all the relevant values
LL | // !useful, !reachable
LL | _a => {}
| ^^ no value can reach this

error[E0004]: non-exhaustive patterns: `&Some(!)` not covered
--> $DIR/empty-types.rs:451:11
|
Expand Down Expand Up @@ -744,7 +558,7 @@ LL ~ None => {},
LL + Some(!)
|

error: aborting due to 65 previous errors; 1 warning emitted
error: aborting due to 42 previous errors; 1 warning emitted

Some errors have detailed explanations: E0004, E0005.
For more information about an error, try `rustc --explain E0004`.
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