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diannedianne
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add exhaustiveness/usefulness tests for deref patterns
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‎tests/ui/pattern/deref-patterns/usefulness/empty-types.rs

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//! Test that the place behind a deref pattern is treated as maybe-invalid, and thus empty arms
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//! cannot be omitted. This is handled the same as for refs and union fields, so this leaves the
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//! bulk of the testing to `tests/ui/pattern/usefulness/empty-types.rs`.
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// FIXME(deref_patterns): On stabilization, cases for deref patterns could be worked into that file
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// to keep the tests for empty types in one place and test more thoroughly.
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#![feature(deref_patterns)]
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#![expect(incomplete_features)]
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#![deny(unreachable_patterns)]
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enum Void {}
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fn main() {
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// Sanity check: matching on an empty type without pointer indirection lets us omit arms.
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let opt_void: Option<Void> = None;
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match opt_void {
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None => {}
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}
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// But if we hide it behind a smart pointer, we need an arm.
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let box_opt_void: Box<Option<Void>> = Box::new(None);
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match box_opt_void {
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//~^ ERROR non-exhaustive patterns: `deref!(Some(_))` not covered
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None => {}
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}
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match box_opt_void {
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None => {}
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Some(_) => {}
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}
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match box_opt_void {
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None => {}
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_ => {}
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}
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// For consistency, this behaves the same as if we manually dereferenced the scrutinee.
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match *box_opt_void {
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//~^ ERROR non-exhaustive patterns: `Some(_)` not covered
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None => {}
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}
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match *box_opt_void {
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None => {}
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Some(_) => {}
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}
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match *box_opt_void {
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None => {}
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_ => {}
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}
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}

‎tests/ui/pattern/deref-patterns/usefulness/empty-types.stderr

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error[E0004]: non-exhaustive patterns: `deref!(Some(_))` not covered
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--> $DIR/empty-types.rs:21:11
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|
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LL | match box_opt_void {
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| ^^^^^^^^^^^^ pattern `deref!(Some(_))` not covered
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|
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note: `Box<Option<Void>>` defined here
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--> $SRC_DIR/alloc/src/boxed.rs:LL:COL
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= note: the matched value is of type `Box<Option<Void>>`
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= note: `Void` is uninhabited but is not being matched by value, so a wildcard `_` is required
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help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
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|
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LL ~ None => {},
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LL + deref!(Some(_)) => todo!()
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|
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error[E0004]: non-exhaustive patterns: `Some(_)` not covered
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--> $DIR/empty-types.rs:35:11
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|
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LL | match *box_opt_void {
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| ^^^^^^^^^^^^^ pattern `Some(_)` not covered
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|
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note: `Option<Void>` defined here
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--> $SRC_DIR/core/src/option.rs:LL:COL
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::: $SRC_DIR/core/src/option.rs:LL:COL
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|
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= note: not covered
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= note: the matched value is of type `Option<Void>`
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= note: `Void` is uninhabited but is not being matched by value, so a wildcard `_` is required
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help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
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|
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LL ~ None => {},
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LL + Some(_) => todo!()
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|
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0004`.

‎tests/ui/pattern/deref-patterns/usefulness/non-exhaustive.rs

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//! Test non-exhaustive matches involving deref patterns.
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#![feature(deref_patterns)]
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#![expect(incomplete_features)]
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#![deny(unreachable_patterns)]
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fn main() {
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match Box::new(false) {
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//~^ ERROR non-exhaustive patterns: `deref!(true)` not covered
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false => {}
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}
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match Box::new(Box::new(false)) {
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//~^ ERROR non-exhaustive patterns: `deref!(deref!(false))` not covered
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true => {}
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}
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match Box::new((true, Box::new(false))) {
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//~^ ERROR non-exhaustive patterns: `deref!((false, deref!(false)))` and `deref!((true, deref!(true)))` not covered
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(true, false) => {}
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(false, true) => {}
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}
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enum T { A, B, C }
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match Box::new((Box::new(T::A), Box::new(T::A))) {
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//~^ ERROR non-exhaustive patterns: `deref!((deref!(T::C), _))` not covered
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(T::A | T::B, T::C) => {}
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}
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}

‎tests/ui/pattern/deref-patterns/usefulness/non-exhaustive.stderr

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error[E0004]: non-exhaustive patterns: `deref!(true)` not covered
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--> $DIR/non-exhaustive.rs:7:11
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|
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LL | match Box::new(false) {
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| ^^^^^^^^^^^^^^^ pattern `deref!(true)` not covered
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|
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note: `Box<bool>` defined here
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--> $SRC_DIR/alloc/src/boxed.rs:LL:COL
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= note: the matched value is of type `Box<bool>`
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help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
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|
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LL ~ false => {},
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LL + deref!(true) => todo!()
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|
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error[E0004]: non-exhaustive patterns: `deref!(deref!(false))` not covered
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--> $DIR/non-exhaustive.rs:12:11
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|
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LL | match Box::new(Box::new(false)) {
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| ^^^^^^^^^^^^^^^^^^^^^^^^^ pattern `deref!(deref!(false))` not covered
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|
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note: `Box<Box<bool>>` defined here
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--> $SRC_DIR/alloc/src/boxed.rs:LL:COL
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= note: the matched value is of type `Box<Box<bool>>`
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help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
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|
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LL ~ true => {},
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LL + deref!(deref!(false)) => todo!()
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|
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error[E0004]: non-exhaustive patterns: `deref!((false, deref!(false)))` and `deref!((true, deref!(true)))` not covered
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--> $DIR/non-exhaustive.rs:17:11
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|
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LL | match Box::new((true, Box::new(false))) {
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ patterns `deref!((false, deref!(false)))` and `deref!((true, deref!(true)))` not covered
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|
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note: `Box<(bool, Box<bool>)>` defined here
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--> $SRC_DIR/alloc/src/boxed.rs:LL:COL
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= note: the matched value is of type `Box<(bool, Box<bool>)>`
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help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern, a match arm with multiple or-patterns as shown, or multiple match arms
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|
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LL ~ (false, true) => {},
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LL + deref!((false, deref!(false))) | deref!((true, deref!(true))) => todo!()
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|
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error[E0004]: non-exhaustive patterns: `deref!((deref!(T::C), _))` not covered
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--> $DIR/non-exhaustive.rs:24:11
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|
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LL | match Box::new((Box::new(T::A), Box::new(T::A))) {
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ pattern `deref!((deref!(T::C), _))` not covered
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|
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note: `Box<(Box<T>, Box<T>)>` defined here
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--> $SRC_DIR/alloc/src/boxed.rs:LL:COL
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= note: the matched value is of type `Box<(Box<T>, Box<T>)>`
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help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
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|
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LL ~ (T::A | T::B, T::C) => {},
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LL + deref!((deref!(T::C), _)) => todo!()
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|
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error: aborting due to 4 previous errors
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For more information about this error, try `rustc --explain E0004`.

‎tests/ui/pattern/deref-patterns/usefulness/unreachable-patterns.rs

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//! Test unreachable patterns involving deref patterns.
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#![feature(deref_patterns)]
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#![expect(incomplete_features)]
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#![deny(unreachable_patterns)]
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fn main() {
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match Box::new(false) {
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true => {}
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false => {}
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false => {} //~ ERROR unreachable pattern
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}
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match Box::new(Box::new(false)) {
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true => {}
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false => {}
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true => {} //~ ERROR unreachable pattern
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}
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match Box::new((true, Box::new(false))) {
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(true, _) => {}
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(_, true) => {}
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(false, false) => {}
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_ => {} //~ ERROR unreachable pattern
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}
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enum T { A, B, C }
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match Box::new((Box::new(T::A), Box::new(T::A))) {
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(T::A | T::B, T::A | T::C) => {}
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(T::A, T::C) => {} //~ ERROR unreachable pattern
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(T::B, T::A) => {} //~ ERROR unreachable pattern
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_ => {}
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}
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}

‎tests/ui/pattern/deref-patterns/usefulness/unreachable-patterns.stderr

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error: unreachable pattern
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--> $DIR/unreachable-patterns.rs:10:9
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|
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LL | false => {}
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| ----- matches all the relevant values
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LL | false => {}
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| ^^^^^ no value can reach this
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|
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note: the lint level is defined here
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--> $DIR/unreachable-patterns.rs:4:9
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|
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LL | #![deny(unreachable_patterns)]
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| ^^^^^^^^^^^^^^^^^^^^
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error: unreachable pattern
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--> $DIR/unreachable-patterns.rs:16:9
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|
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LL | true => {}
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| ---- matches all the relevant values
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LL | false => {}
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LL | true => {}
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| ^^^^ no value can reach this
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error: unreachable pattern
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--> $DIR/unreachable-patterns.rs:23:9
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|
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LL | _ => {}
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| ^ no value can reach this
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|
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note: multiple earlier patterns match some of the same values
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--> $DIR/unreachable-patterns.rs:23:9
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|
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LL | (true, _) => {}
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| --------- matches some of the same values
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LL | (_, true) => {}
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| --------- matches some of the same values
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LL | (false, false) => {}
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| -------------- matches some of the same values
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LL | _ => {}
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| ^ collectively making this unreachable
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error: unreachable pattern
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--> $DIR/unreachable-patterns.rs:29:9
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|
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LL | (T::A | T::B, T::A | T::C) => {}
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| -------------------------- matches all the relevant values
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LL | (T::A, T::C) => {}
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| ^^^^^^^^^^^^ no value can reach this
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error: unreachable pattern
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--> $DIR/unreachable-patterns.rs:30:9
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|
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LL | (T::A | T::B, T::A | T::C) => {}
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| -------------------------- matches all the relevant values
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LL | (T::A, T::C) => {}
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LL | (T::B, T::A) => {}
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| ^^^^^^^^^^^^ no value can reach this
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error: aborting due to 5 previous errors
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