Test empty types better

tests/ui/pattern/usefulness/empty-match-check-notes.exhaustive_patterns.stderr

@@ -0,0 +1,63 @@
+error: unreachable pattern
+  --> $DIR/empty-match-check-notes.rs:17:9
+   |
+LL |         _ => {}
+   |         ^
+   |
+note: the lint level is defined here
+  --> $DIR/empty-match-check-notes.rs:7:9
+   |
+LL | #![deny(unreachable_patterns)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/empty-match-check-notes.rs:20:9
+   |
+LL |         _ if false => {}
+   |         ^
+
+error: unreachable pattern
+  --> $DIR/empty-match-check-notes.rs:27:9
+   |
+LL |         _ => {}
+   |         ^
+
+error: unreachable pattern
+  --> $DIR/empty-match-check-notes.rs:30:9
+   |
+LL |         _ if false => {}
+   |         ^
+
+error[E0005]: refutable pattern in local binding
+  --> $DIR/empty-match-check-notes.rs:35:9
+   |
+LL |     let None = x;
+   |         ^^^^ pattern `Some(_)` not covered
+   |
+   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
+   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
+   = note: pattern `Some(_)` is currently uninhabited, but this variant contains private fields which may become inhabited in the future
+   = note: the matched value is of type `Option<SecretlyUninhabitedForeignStruct>`
+help: you might want to use `if let` to ignore the variant that isn't matched
+   |
+LL |     if let None = x { todo!() };
+   |     ++              +++++++++++
+
+error[E0004]: non-exhaustive patterns: `_` not covered
+  --> $DIR/empty-match-check-notes.rs:45:11
+   |
+LL |     match 0u8 {
+   |           ^^^ pattern `_` not covered
+   |
+   = note: the matched value is of type `u8`
+   = note: match arms with guards don't count towards exhaustivity
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
+   |
+LL ~         _ if false => {},
+LL +         _ => todo!()
+   |
+
+error: aborting due to 6 previous errors
+
+Some errors have detailed explanations: E0004, E0005.
+For more information about an error, try `rustc --explain E0004`.

tests/ui/pattern/usefulness/empty-match-check-notes.normal.stderr

@@ -0,0 +1,62 @@
+error: unreachable pattern
+  --> $DIR/empty-match-check-notes.rs:17:9
+   |
+LL |         _ => {}
+   |         ^
+   |
+note: the lint level is defined here
+  --> $DIR/empty-match-check-notes.rs:7:9
+   |
+LL | #![deny(unreachable_patterns)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/empty-match-check-notes.rs:20:9
+   |
+LL |         _ if false => {}
+   |         ^
+
+error: unreachable pattern
+  --> $DIR/empty-match-check-notes.rs:27:9
+   |
+LL |         _ => {}
+   |         ^
+
+error: unreachable pattern
+  --> $DIR/empty-match-check-notes.rs:30:9
+   |
+LL |         _ if false => {}
+   |         ^
+
+error[E0005]: refutable pattern in local binding
+  --> $DIR/empty-match-check-notes.rs:35:9
+   |
+LL |     let None = x;
+   |         ^^^^ pattern `Some(_)` not covered
+   |
+   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
+   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
+   = note: the matched value is of type `Option<SecretlyUninhabitedForeignStruct>`
+help: you might want to use `if let` to ignore the variant that isn't matched
+   |
+LL |     if let None = x { todo!() };
+   |     ++              +++++++++++
+
+error[E0004]: non-exhaustive patterns: `_` not covered
+  --> $DIR/empty-match-check-notes.rs:45:11
+   |
+LL |     match 0u8 {
+   |           ^^^ pattern `_` not covered
+   |
+   = note: the matched value is of type `u8`
+   = note: match arms with guards don't count towards exhaustivity
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
+   |
+LL ~         _ if false => {},
+LL +         _ => todo!()
+   |
+
+error: aborting due to 6 previous errors
+
+Some errors have detailed explanations: E0004, E0005.
+For more information about an error, try `rustc --explain E0004`.

tests/ui/pattern/usefulness/empty-match-check-notes.rs

@@ -0,0 +1,52 @@
+// aux-build:empty.rs
+// revisions: normal exhaustive_patterns
+//
+// This tests a match with no arms on various types, and checks NOTEs.
+#![feature(never_type)]
+#![cfg_attr(exhaustive_patterns, feature(exhaustive_patterns))]
+#![deny(unreachable_patterns)]
+//~^ NOTE the lint level is defined here
+
+extern crate empty;
+
+enum EmptyEnum {}
+
+fn empty_enum(x: EmptyEnum) {
+    match x {} // ok
+    match x {
+        _ => {} //~ ERROR unreachable pattern
+    }
+    match x {
+        _ if false => {} //~ ERROR unreachable pattern
+    }
+}
+
+fn empty_foreign_enum(x: empty::EmptyForeignEnum) {
+    match x {} // ok
+    match x {
+        _ => {} //~ ERROR unreachable pattern
+    }
+    match x {
+        _ if false => {} //~ ERROR unreachable pattern
+    }
+}
+
+fn empty_foreign_enum_private(x: Option<empty::SecretlyUninhabitedForeignStruct>) {
+    let None = x;
+    //~^ ERROR refutable pattern in local binding
+    //~| NOTE `let` bindings require an "irrefutable pattern"
+    //~| NOTE for more information, visit
+    //~| NOTE the matched value is of type
+    //~| NOTE pattern `Some(_)` not covered
+    //[exhaustive_patterns]~| NOTE currently uninhabited, but this variant contains private fields
+}
+
+fn main() {
+    match 0u8 {
+        //~^ ERROR `_` not covered
+        //~| NOTE the matched value is of type
+        //~| NOTE match arms with guards don't count towards exhaustivity
+        //~| NOTE pattern `_` not covered
+        _ if false => {}
+    }
+}