move from non zero impls to `libcore/convert/num.rs`

31 files changed, 555 insertions, 43 deletions

diff --git a/src/test/ui/pattern/issue-53820-slice-pattern-large-array.rs b/src/test/ui/pattern/issue-53820-slice-pattern-large-array.rs
new file mode 100644
index 00000000000..c910cded96b
--- /dev/null
+++ b/src/test/ui/pattern/issue-53820-slice-pattern-large-array.rs
@@ -0,0 +1,13 @@
+// check-pass
+
+// This used to cause a stack overflow in the compiler.
+
+#![feature(slice_patterns)]
+
+fn main() {
+    const LARGE_SIZE: usize = 1024 * 1024;
+    let [..] = [0u8; LARGE_SIZE];
+    match [0u8; LARGE_SIZE] {
+        [..] => {}
+    }
+}
diff --git a/src/test/ui/pattern/pat-tuple-bad-type.stderr b/src/test/ui/pattern/pat-tuple-bad-type.stderr
index 3da3bcb635f..95cca38f7de 100644
--- a/src/test/ui/pattern/pat-tuple-bad-type.stderr
+++ b/src/test/ui/pattern/pat-tuple-bad-type.stderr
@@ -13,10 +13,7 @@ error[E0308]: mismatched types
   --> $DIR/pat-tuple-bad-type.rs:10:9
    |
 LL |         (..) => {}
-   |         ^^^^ expected u8, found ()
-   |
-   = note: expected type `u8`
-              found type `()`
+   |         ^^^^ expected `u8`, found `()`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/pattern/pat-tuple-overfield.stderr b/src/test/ui/pattern/pat-tuple-overfield.stderr
index e64b6efb08d..25d02b8627c 100644
--- a/src/test/ui/pattern/pat-tuple-overfield.stderr
+++ b/src/test/ui/pattern/pat-tuple-overfield.stderr
@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |         (1, 2, 3, 4) => {}
    |         ^^^^^^^^^^^^ expected a tuple with 3 elements, found one with 4 elements
    |
-   = note: expected type `({integer}, {integer}, {integer})`
-              found type `(_, _, _, _)`
+   = note: expected tuple `({integer}, {integer}, {integer})`
+              found tuple `(_, _, _, _)`
 
 error[E0308]: mismatched types
   --> $DIR/pat-tuple-overfield.rs:6:9
@@ -13,8 +13,8 @@ error[E0308]: mismatched types
 LL |         (1, 2, .., 3, 4) => {}
    |         ^^^^^^^^^^^^^^^^ expected a tuple with 3 elements, found one with 4 elements
    |
-   = note: expected type `({integer}, {integer}, {integer})`
-              found type `(_, _, _, _)`
+   = note: expected tuple `({integer}, {integer}, {integer})`
+              found tuple `(_, _, _, _)`
 
 error[E0023]: this pattern has 4 fields, but the corresponding tuple struct has 3 fields
   --> $DIR/pat-tuple-overfield.rs:10:9
diff --git a/src/test/ui/pattern/patkind-litrange-no-expr.stderr b/src/test/ui/pattern/patkind-litrange-no-expr.stderr
index 7474d326793..78768d282e7 100644
--- a/src/test/ui/pattern/patkind-litrange-no-expr.stderr
+++ b/src/test/ui/pattern/patkind-litrange-no-expr.stderr
@@ -7,11 +7,11 @@ LL |     Arith = 1 + 1,
 error[E0029]: only char and numeric types are allowed in range patterns
   --> $DIR/patkind-litrange-no-expr.rs:20:13
    |
+LL |                 $( $value ..= 42 => Some($name::$variant), )* // PatKind::Range
+   |                               -- this is of type `{integer}`
+...
 LL |     Arith = 1 + 1,
-   |             ^^^^^ ranges require char or numeric types
-   |
-   = note: start type: {integer}
-   = note: end type: {integer}
+   |             ^^^^^ this is of type `_` but it should be `char` or numeric
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/pattern/pattern-error-continue.rs b/src/test/ui/pattern/pattern-error-continue.rs
index 79cc4b552a7..8635622ab37 100644
--- a/src/test/ui/pattern/pattern-error-continue.rs
+++ b/src/test/ui/pattern/pattern-error-continue.rs
@@ -21,15 +21,13 @@ fn main() {
     match 'c' {
         S { .. } => (),
         //~^ ERROR mismatched types
-        //~| expected type `char`
-        //~| found type `S`
-        //~| expected char, found struct `S`
+        //~| expected `char`, found struct `S`
 
         _ => ()
     }
     f(true);
     //~^ ERROR mismatched types
-    //~| expected char, found bool
+    //~| expected `char`, found `bool`
 
     match () {
         E::V => {} //~ ERROR failed to resolve: use of undeclared type or module `E`
diff --git a/src/test/ui/pattern/pattern-error-continue.stderr b/src/test/ui/pattern/pattern-error-continue.stderr
index 5a7dab30d83..2f9fe1981bc 100644
--- a/src/test/ui/pattern/pattern-error-continue.stderr
+++ b/src/test/ui/pattern/pattern-error-continue.stderr
@@ -1,5 +1,5 @@
 error[E0433]: failed to resolve: use of undeclared type or module `E`
-  --> $DIR/pattern-error-continue.rs:35:9
+  --> $DIR/pattern-error-continue.rs:33:9
    |
 LL |         E::V => {}
    |         ^ use of undeclared type or module `E`
@@ -30,16 +30,13 @@ error[E0308]: mismatched types
 LL |     match 'c' {
    |           --- this match expression has type `char`
 LL |         S { .. } => (),
-   |         ^^^^^^^^ expected char, found struct `S`
-   |
-   = note: expected type `char`
-              found type `S`
+   |         ^^^^^^^^ expected `char`, found struct `S`
 
 error[E0308]: mismatched types
-  --> $DIR/pattern-error-continue.rs:30:7
+  --> $DIR/pattern-error-continue.rs:28:7
    |
 LL |     f(true);
-   |       ^^^^ expected char, found bool
+   |       ^^^^ expected `char`, found `bool`
 
 error: aborting due to 5 previous errors
 
diff --git a/src/test/ui/pattern/pattern-ident-path-generics.stderr b/src/test/ui/pattern/pattern-ident-path-generics.stderr
index bfc10c5f866..338eb6ff0c8 100644
--- a/src/test/ui/pattern/pattern-ident-path-generics.stderr
+++ b/src/test/ui/pattern/pattern-ident-path-generics.stderr
@@ -2,10 +2,10 @@ error[E0308]: mismatched types
   --> $DIR/pattern-ident-path-generics.rs:3:9
    |
 LL |         None::<isize> => {}
-   |         ^^^^^^^^^^^^^ expected &str, found isize
+   |         ^^^^^^^^^^^^^ expected `&str`, found `isize`
    |
-   = note: expected type `std::option::Option<&str>`
-              found type `std::option::Option<isize>`
+   = note: expected enum `std::option::Option<&str>`
+              found enum `std::option::Option<isize>`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/pattern/pattern-tyvar.stderr b/src/test/ui/pattern/pattern-tyvar.stderr
index 54834703467..b2afeacdf68 100644
--- a/src/test/ui/pattern/pattern-tyvar.stderr
+++ b/src/test/ui/pattern/pattern-tyvar.stderr
@@ -4,10 +4,10 @@ error[E0308]: mismatched types
 LL |     match t {
    |           - this match expression has type `std::option::Option<std::vec::Vec<isize>>`
 LL |       Bar::T1(_, Some::<isize>(x)) => {
-   |                  ^^^^^^^^^^^^^^^^ expected struct `std::vec::Vec`, found isize
+   |                  ^^^^^^^^^^^^^^^^ expected struct `std::vec::Vec`, found `isize`
    |
-   = note: expected type `std::option::Option<std::vec::Vec<isize>>`
-              found type `std::option::Option<isize>`
+   = note: expected enum `std::option::Option<std::vec::Vec<isize>>`
+              found enum `std::option::Option<isize>`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/pattern/usefulness/65413-constants-and-slices-exhaustiveness.rs b/src/test/ui/pattern/usefulness/65413-constants-and-slices-exhaustiveness.rs
new file mode 100644
index 00000000000..6c54c938bf1
--- /dev/null
+++ b/src/test/ui/pattern/usefulness/65413-constants-and-slices-exhaustiveness.rs
@@ -0,0 +1,15 @@
+// check-pass
+#![feature(slice_patterns)]
+#![deny(unreachable_patterns)]
+
+const C0: &'static [u8] = b"\x00";
+
+fn main() {
+    let x: &[u8] = &[0];
+    match x {
+        &[] => {}
+        &[1..=255] => {}
+        C0 => {}
+        &[_, _, ..] => {}
+    }
+}
diff --git a/src/test/ui/pattern/usefulness/exhaustive_integer_patterns.rs b/src/test/ui/pattern/usefulness/exhaustive_integer_patterns.rs
index 59f74919897..d379dc44bf1 100644
--- a/src/test/ui/pattern/usefulness/exhaustive_integer_patterns.rs
+++ b/src/test/ui/pattern/usefulness/exhaustive_integer_patterns.rs
@@ -154,4 +154,19 @@ fn main() {
     match 0u128 { //~ ERROR non-exhaustive patterns
         4 ..= u128::MAX => {}
     }
+
+    const FOO: i32 = 42;
+    const BAR: &i32 = &42;
+    match &0 {
+        &42 => {}
+        &FOO => {} //~ ERROR unreachable pattern
+        BAR => {} // Not detected as unreachable because `try_eval_bits` fails on `BAR`.
+        _ => {}
+    }
+
+    // Regression test, see https://github.com/rust-lang/rust/pull/66326#issuecomment-552889933
+    match &0 {
+        BAR => {} // ok
+        _ => {}
+    }
 }
diff --git a/src/test/ui/pattern/usefulness/exhaustive_integer_patterns.stderr b/src/test/ui/pattern/usefulness/exhaustive_integer_patterns.stderr
index 7a3a36a820c..0fbeb981ea0 100644
--- a/src/test/ui/pattern/usefulness/exhaustive_integer_patterns.stderr
+++ b/src/test/ui/pattern/usefulness/exhaustive_integer_patterns.stderr
@@ -118,6 +118,12 @@ LL |     match 0u128 {
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
-error: aborting due to 14 previous errors
+error: unreachable pattern
+  --> $DIR/exhaustive_integer_patterns.rs:162:9
+   |
+LL |         &FOO => {}
+   |         ^^^^
+
+error: aborting due to 15 previous errors
 
 For more information about this error, try `rustc --explain E0004`.
diff --git a/src/test/ui/pattern/usefulness/match-byte-array-patterns-2.stderr b/src/test/ui/pattern/usefulness/match-byte-array-patterns-2.stderr
index d53e2e25b3d..539aa854f9e 100644
--- a/src/test/ui/pattern/usefulness/match-byte-array-patterns-2.stderr
+++ b/src/test/ui/pattern/usefulness/match-byte-array-patterns-2.stderr
@@ -1,16 +1,16 @@
-error[E0004]: non-exhaustive patterns: `&[_, _, _, _]` not covered
+error[E0004]: non-exhaustive patterns: `&[0u8..=64u8, _, _, _]` and `&[66u8..=std::u8::MAX, _, _, _]` not covered
   --> $DIR/match-byte-array-patterns-2.rs:4:11
    |
 LL |     match buf {
-   |           ^^^ pattern `&[_, _, _, _]` not covered
+   |           ^^^ patterns `&[0u8..=64u8, _, _, _]` and `&[66u8..=std::u8::MAX, _, _, _]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
-error[E0004]: non-exhaustive patterns: `&[]`, `&[_]`, `&[_, _]` and 3 more not covered
+error[E0004]: non-exhaustive patterns: `&[]`, `&[_]`, `&[_, _]` and 2 more not covered
   --> $DIR/match-byte-array-patterns-2.rs:10:11
    |
 LL |     match buf {
-   |           ^^^ patterns `&[]`, `&[_]`, `&[_, _]` and 3 more not covered
+   |           ^^^ patterns `&[]`, `&[_]`, `&[_, _]` and 2 more not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
diff --git a/src/test/ui/pattern/usefulness/match-privately-empty.rs b/src/test/ui/pattern/usefulness/match-privately-empty.rs
index 315eb03d165..ea608651387 100644
--- a/src/test/ui/pattern/usefulness/match-privately-empty.rs
+++ b/src/test/ui/pattern/usefulness/match-privately-empty.rs
@@ -1,4 +1,3 @@
-#![feature(never_type)]
 #![feature(exhaustive_patterns)]
 
 mod private {
diff --git a/src/test/ui/pattern/usefulness/match-privately-empty.stderr b/src/test/ui/pattern/usefulness/match-privately-empty.stderr
index f79d180a1b8..66d0d958774 100644
--- a/src/test/ui/pattern/usefulness/match-privately-empty.stderr
+++ b/src/test/ui/pattern/usefulness/match-privately-empty.stderr
@@ -1,5 +1,5 @@
 error[E0004]: non-exhaustive patterns: `Some(Private { misc: true, .. })` not covered
-  --> $DIR/match-privately-empty.rs:13:11
+  --> $DIR/match-privately-empty.rs:12:11
    |
 LL |     match private::DATA {
    |           ^^^^^^^^^^^^^ pattern `Some(Private { misc: true, .. })` not covered
diff --git a/src/test/ui/pattern/usefulness/match-slice-patterns.rs b/src/test/ui/pattern/usefulness/match-slice-patterns.rs
index afbeb61e441..af7fd53a1f1 100644
--- a/src/test/ui/pattern/usefulness/match-slice-patterns.rs
+++ b/src/test/ui/pattern/usefulness/match-slice-patterns.rs
@@ -2,7 +2,7 @@
 
 fn check(list: &[Option<()>]) {
     match list {
-    //~^ ERROR `&[_, Some(_), None, _]` not covered
+    //~^ ERROR `&[_, Some(_), .., None, _]` not covered
         &[] => {},
         &[_] => {},
         &[_, _] => {},
diff --git a/src/test/ui/pattern/usefulness/match-slice-patterns.stderr b/src/test/ui/pattern/usefulness/match-slice-patterns.stderr
index 24769db34c9..72ae5d5fe3b 100644
--- a/src/test/ui/pattern/usefulness/match-slice-patterns.stderr
+++ b/src/test/ui/pattern/usefulness/match-slice-patterns.stderr
@@ -1,8 +1,8 @@
-error[E0004]: non-exhaustive patterns: `&[_, Some(_), None, _]` not covered
+error[E0004]: non-exhaustive patterns: `&[_, Some(_), .., None, _]` not covered
   --> $DIR/match-slice-patterns.rs:4:11
    |
 LL |     match list {
-   |           ^^^^ pattern `&[_, Some(_), None, _]` not covered
+   |           ^^^^ pattern `&[_, Some(_), .., None, _]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
diff --git a/src/test/ui/pattern/usefulness/non-exhaustive-match.rs b/src/test/ui/pattern/usefulness/non-exhaustive-match.rs
index 0e5a9203c5f..bfca5352353 100644
--- a/src/test/ui/pattern/usefulness/non-exhaustive-match.rs
+++ b/src/test/ui/pattern/usefulness/non-exhaustive-match.rs
@@ -44,7 +44,7 @@ fn main() {
     }
     let vec = vec![0.5f32];
     let vec: &[f32] = &vec;
-    match *vec { //~ ERROR non-exhaustive patterns: `[_, _, _, _]` not covered
+    match *vec { //~ ERROR non-exhaustive patterns: `[_, _, _, _, ..]` not covered
         [0.1, 0.2, 0.3] => (),
         [0.1, 0.2] => (),
         [0.1] => (),
diff --git a/src/test/ui/pattern/usefulness/non-exhaustive-match.stderr b/src/test/ui/pattern/usefulness/non-exhaustive-match.stderr
index 5dba05e1642..577867e4e71 100644
--- a/src/test/ui/pattern/usefulness/non-exhaustive-match.stderr
+++ b/src/test/ui/pattern/usefulness/non-exhaustive-match.stderr
@@ -66,11 +66,11 @@ LL |     match *vec {
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
-error[E0004]: non-exhaustive patterns: `[_, _, _, _]` not covered
+error[E0004]: non-exhaustive patterns: `[_, _, _, _, ..]` not covered
   --> $DIR/non-exhaustive-match.rs:47:11
    |
 LL |     match *vec {
-   |           ^^^^ pattern `[_, _, _, _]` not covered
+   |           ^^^^ pattern `[_, _, _, _, ..]` not covered
    |
    = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
 
diff --git a/src/test/ui/pattern/slice-pattern-const-2.rs b/src/test/ui/pattern/usefulness/slice-pattern-const-2.rs
index a36c550f530..a36c550f530 100644
--- a/src/test/ui/pattern/slice-pattern-const-2.rs
+++ b/src/test/ui/pattern/usefulness/slice-pattern-const-2.rs
diff --git a/src/test/ui/pattern/slice-pattern-const-2.stderr b/src/test/ui/pattern/usefulness/slice-pattern-const-2.stderr
index 0c7401269df..0c7401269df 100644
--- a/src/test/ui/pattern/slice-pattern-const-2.stderr
+++ b/src/test/ui/pattern/usefulness/slice-pattern-const-2.stderr
diff --git a/src/test/ui/pattern/slice-pattern-const-3.rs b/src/test/ui/pattern/usefulness/slice-pattern-const-3.rs
index 8805c43ba02..8805c43ba02 100644
--- a/src/test/ui/pattern/slice-pattern-const-3.rs
+++ b/src/test/ui/pattern/usefulness/slice-pattern-const-3.rs
diff --git a/src/test/ui/pattern/slice-pattern-const-3.stderr b/src/test/ui/pattern/usefulness/slice-pattern-const-3.stderr
index eab4fc3f086..eab4fc3f086 100644
--- a/src/test/ui/pattern/slice-pattern-const-3.stderr
+++ b/src/test/ui/pattern/usefulness/slice-pattern-const-3.stderr
diff --git a/src/test/ui/pattern/slice-pattern-const.rs b/src/test/ui/pattern/usefulness/slice-pattern-const.rs
index f0a04513f91..89195d5b11e 100644
--- a/src/test/ui/pattern/slice-pattern-const.rs
+++ b/src/test/ui/pattern/usefulness/slice-pattern-const.rs
@@ -44,4 +44,11 @@ fn main() {
         b"" => (), //~ ERROR unreachable pattern
         _ => (), //~ ERROR unreachable pattern
     }
+
+    const CONST1: &[bool; 1] = &[true];
+    match &[false] {
+        CONST1 => {}
+        [true] => {} //~ ERROR unreachable pattern
+        [false] => {}
+    }
 }
diff --git a/src/test/ui/pattern/slice-pattern-const.stderr b/src/test/ui/pattern/usefulness/slice-pattern-const.stderr
index 2dd10a0478a..d274d6d7c67 100644
--- a/src/test/ui/pattern/slice-pattern-const.stderr
+++ b/src/test/ui/pattern/usefulness/slice-pattern-const.stderr
@@ -52,5 +52,11 @@ error: unreachable pattern
 LL |         _ => (),
    |         ^
 
-error: aborting due to 8 previous errors
+error: unreachable pattern
+  --> $DIR/slice-pattern-const.rs:51:9
+   |
+LL |         [true] => {}
+   |         ^^^^^^
+
+error: aborting due to 9 previous errors
 
diff --git a/src/test/ui/pattern/usefulness/slice-patterns-exhaustiveness.rs b/src/test/ui/pattern/usefulness/slice-patterns-exhaustiveness.rs
new file mode 100644
index 00000000000..41ba2cc4501
--- /dev/null
+++ b/src/test/ui/pattern/usefulness/slice-patterns-exhaustiveness.rs
@@ -0,0 +1,107 @@
+#![feature(slice_patterns)]
+
+fn main() {
+    let s: &[bool] = &[true; 0];
+    let s1: &[bool; 1] = &[false; 1];
+    let s2: &[bool; 2] = &[false; 2];
+    let s3: &[bool; 3] = &[false; 3];
+    let s10: &[bool; 10] = &[false; 10];
+
+    match s2 {
+    //~^ ERROR `&[false, _]` not covered
+        [true, .., true] => {}
+    }
+    match s3 {
+    //~^ ERROR `&[false, ..]` not covered
+        [true, .., true] => {}
+    }
+    match s10 {
+    //~^ ERROR `&[false, ..]` not covered
+        [true, .., true] => {}
+    }
+
+    match s1 {
+        [true, ..] => {}
+        [.., false] => {}
+    }
+    match s2 {
+    //~^ ERROR `&[false, true]` not covered
+        [true, ..] => {}
+        [.., false] => {}
+    }
+    match s3 {
+    //~^ ERROR `&[false, .., true]` not covered
+        [true, ..] => {}
+        [.., false] => {}
+    }
+    match s {
+    //~^ ERROR `&[false, .., true]` not covered
+        [] => {}
+        [true, ..] => {}
+        [.., false] => {}
+    }
+
+    match s {
+    //~^ ERROR `&[_, ..]` not covered
+        [] => {}
+    }
+    match s {
+    //~^ ERROR `&[_, _, ..]` not covered
+        [] => {}
+        [_] => {}
+    }
+    match s {
+    //~^ ERROR `&[false, ..]` not covered
+        [] => {}
+        [true, ..] => {}
+    }
+    match s {
+    //~^ ERROR `&[false, _, ..]` not covered
+        [] => {}
+        [_] => {}
+        [true, ..] => {}
+    }
+    match s {
+    //~^ ERROR `&[_, .., false]` not covered
+        [] => {}
+        [_] => {}
+        [.., true] => {}
+    }
+
+    match s {
+    //~^ ERROR `&[_, _, .., true]` not covered
+        [] => {}
+        [_] => {}
+        [_, _] => {}
+        [.., false] => {}
+    }
+    match s {
+    //~^ ERROR `&[true, _, .., _]` not covered
+        [] => {}
+        [_] => {}
+        [_, _] => {}
+        [false, .., false] => {}
+    }
+
+    const CONST: &[bool] = &[true];
+    match s {
+    //~^ ERROR `&[..]` not covered
+        CONST => {}
+    }
+    match s {
+    //~^ ERROR `&[true]` not covered
+        [] => {},
+        [false] => {},
+        CONST => {},
+        [_, _, ..] => {}
+    }
+    const CONST1: &[bool; 1] = &[true];
+    match s1 {
+    //~^ ERROR `&[false]` not covered
+        CONST1 => {}
+    }
+    match s1 {
+        CONST1 => {}
+        [false] => {}
+    }
+}
diff --git a/src/test/ui/pattern/usefulness/slice-patterns-exhaustiveness.stderr b/src/test/ui/pattern/usefulness/slice-patterns-exhaustiveness.stderr
new file mode 100644
index 00000000000..8cb342f33df
--- /dev/null
+++ b/src/test/ui/pattern/usefulness/slice-patterns-exhaustiveness.stderr
@@ -0,0 +1,131 @@
+error[E0004]: non-exhaustive patterns: `&[false, _]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:10:11
+   |
+LL |     match s2 {
+   |           ^^ pattern `&[false, _]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[false, ..]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:14:11
+   |
+LL |     match s3 {
+   |           ^^ pattern `&[false, ..]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[false, ..]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:18:11
+   |
+LL |     match s10 {
+   |           ^^^ pattern `&[false, ..]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[false, true]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:27:11
+   |
+LL |     match s2 {
+   |           ^^ pattern `&[false, true]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[false, .., true]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:32:11
+   |
+LL |     match s3 {
+   |           ^^ pattern `&[false, .., true]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[false, .., true]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:37:11
+   |
+LL |     match s {
+   |           ^ pattern `&[false, .., true]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[_, ..]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:44:11
+   |
+LL |     match s {
+   |           ^ pattern `&[_, ..]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[_, _, ..]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:48:11
+   |
+LL |     match s {
+   |           ^ pattern `&[_, _, ..]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[false, ..]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:53:11
+   |
+LL |     match s {
+   |           ^ pattern `&[false, ..]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[false, _, ..]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:58:11
+   |
+LL |     match s {
+   |           ^ pattern `&[false, _, ..]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[_, .., false]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:64:11
+   |
+LL |     match s {
+   |           ^ pattern `&[_, .., false]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[_, _, .., true]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:71:11
+   |
+LL |     match s {
+   |           ^ pattern `&[_, _, .., true]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[true, _, .., _]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:78:11
+   |
+LL |     match s {
+   |           ^ pattern `&[true, _, .., _]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[..]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:87:11
+   |
+LL |     match s {
+   |           ^ pattern `&[..]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[true]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:91:11
+   |
+LL |     match s {
+   |           ^ pattern `&[true]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error[E0004]: non-exhaustive patterns: `&[false]` not covered
+  --> $DIR/slice-patterns-exhaustiveness.rs:99:11
+   |
+LL |     match s1 {
+   |           ^^ pattern `&[false]` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error: aborting due to 16 previous errors
+
+For more information about this error, try `rustc --explain E0004`.
diff --git a/src/test/ui/pattern/usefulness/slice-patterns-irrefutable.rs b/src/test/ui/pattern/usefulness/slice-patterns-irrefutable.rs
new file mode 100644
index 00000000000..3b716bae772
--- /dev/null
+++ b/src/test/ui/pattern/usefulness/slice-patterns-irrefutable.rs
@@ -0,0 +1,27 @@
+// check-pass
+#![feature(slice_patterns)]
+
+fn main() {
+    let s: &[bool] = &[true; 0];
+    let s0: &[bool; 0] = &[];
+    let s1: &[bool; 1] = &[false; 1];
+    let s2: &[bool; 2] = &[false; 2];
+
+    let [] = s0;
+    let [_] = s1;
+    let [_, _] = s2;
+
+    let [..] = s;
+    let [..] = s0;
+    let [..] = s1;
+    let [..] = s2;
+
+    let [_, ..] = s1;
+    let [.., _] = s1;
+    let [_, ..] = s2;
+    let [.., _] = s2;
+
+    let [_, _, ..] = s2;
+    let [_, .., _] = s2;
+    let [.., _, _] = s2;
+}
diff --git a/src/test/ui/pattern/usefulness/slice-patterns-reachability.rs b/src/test/ui/pattern/usefulness/slice-patterns-reachability.rs
new file mode 100644
index 00000000000..cd229a0fcbe
--- /dev/null
+++ b/src/test/ui/pattern/usefulness/slice-patterns-reachability.rs
@@ -0,0 +1,26 @@
+#![feature(slice_patterns)]
+#![deny(unreachable_patterns)]
+
+fn main() {
+    let s: &[bool] = &[];
+
+    match s {
+        [true, ..] => {}
+        [true, ..] => {} //~ ERROR unreachable pattern
+        [true] => {} //~ ERROR unreachable pattern
+        [..] => {}
+    }
+    match s {
+        [.., true] => {}
+        [.., true] => {} //~ ERROR unreachable pattern
+        [true] => {} //~ ERROR unreachable pattern
+        [..] => {}
+    }
+    match s {
+        [false, .., true] => {}
+        [false, .., true] => {} //~ ERROR unreachable pattern
+        [false, true] => {} //~ ERROR unreachable pattern
+        [false] => {}
+        [..] => {}
+    }
+}
diff --git a/src/test/ui/pattern/usefulness/slice-patterns-reachability.stderr b/src/test/ui/pattern/usefulness/slice-patterns-reachability.stderr
new file mode 100644
index 00000000000..333ce170283
--- /dev/null
+++ b/src/test/ui/pattern/usefulness/slice-patterns-reachability.stderr
@@ -0,0 +1,44 @@
+error: unreachable pattern
+  --> $DIR/slice-patterns-reachability.rs:9:9
+   |
+LL |         [true, ..] => {}
+   |         ^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/slice-patterns-reachability.rs:2:9
+   |
+LL | #![deny(unreachable_patterns)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/slice-patterns-reachability.rs:10:9
+   |
+LL |         [true] => {}
+   |         ^^^^^^
+
+error: unreachable pattern
+  --> $DIR/slice-patterns-reachability.rs:15:9
+   |
+LL |         [.., true] => {}
+   |         ^^^^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/slice-patterns-reachability.rs:16:9
+   |
+LL |         [true] => {}
+   |         ^^^^^^
+
+error: unreachable pattern
+  --> $DIR/slice-patterns-reachability.rs:21:9
+   |
+LL |         [false, .., true] => {}
+   |         ^^^^^^^^^^^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/slice-patterns-reachability.rs:22:9
+   |
+LL |         [false, true] => {}
+   |         ^^^^^^^^^^^^^
+
+error: aborting due to 6 previous errors
+
diff --git a/src/test/ui/pattern/usefulness/top-level-alternation.rs b/src/test/ui/pattern/usefulness/top-level-alternation.rs
new file mode 100644
index 00000000000..4b47b978930
--- /dev/null
+++ b/src/test/ui/pattern/usefulness/top-level-alternation.rs
@@ -0,0 +1,56 @@
+#![deny(unreachable_patterns)]
+
+fn main() {
+    while let 0..=2 | 1 = 0 {} //~ ERROR unreachable pattern
+    if let 0..=2 | 1 = 0 {} //~ ERROR unreachable pattern
+
+    match 0u8 {
+        0
+            | 0 => {} //~ ERROR unreachable pattern
+        _ => {}
+    }
+    match Some(0u8) {
+        Some(0)
+            | Some(0) => {} //~ ERROR unreachable pattern
+        _ => {}
+    }
+    match (0u8, 0u8) {
+        (0, _) | (_, 0) => {}
+        (0, 0) => {} //~ ERROR unreachable pattern
+        (1, 1) => {}
+        _ => {}
+    }
+    match (0u8, 0u8) {
+        (0, 1) | (2, 3) => {}
+        (0, 3) => {}
+        (2, 1) => {}
+        _ => {}
+    }
+    match (0u8, 0u8) {
+        (_, 0) | (_, 1) => {}
+        _ => {}
+    }
+    match (0u8, 0u8) {
+        (0, _) | (1, _) => {}
+        _ => {}
+    }
+    match Some(0u8) {
+        None | Some(_) => {}
+        _ => {} //~ ERROR unreachable pattern
+    }
+    match Some(0u8) {
+        None | Some(_) => {}
+        Some(_) => {} //~ ERROR unreachable pattern
+        None => {} //~ ERROR unreachable pattern
+    }
+    match Some(0u8) {
+        Some(_) => {}
+        None => {}
+        None | Some(_) => {} //~ ERROR unreachable pattern
+    }
+    match 0u8 {
+        1 | 2 => {},
+        1..=2 => {}, //~ ERROR unreachable pattern
+        _ => {},
+    }
+}
diff --git a/src/test/ui/pattern/usefulness/top-level-alternation.stderr b/src/test/ui/pattern/usefulness/top-level-alternation.stderr
new file mode 100644
index 00000000000..7c7c4fc4eba
--- /dev/null
+++ b/src/test/ui/pattern/usefulness/top-level-alternation.stderr
@@ -0,0 +1,68 @@
+error: unreachable pattern
+  --> $DIR/top-level-alternation.rs:4:23
+   |
+LL |     while let 0..=2 | 1 = 0 {}
+   |                       ^
+   |
+note: lint level defined here
+  --> $DIR/top-level-alternation.rs:1:9
+   |
+LL | #![deny(unreachable_patterns)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/top-level-alternation.rs:5:20
+   |
+LL |     if let 0..=2 | 1 = 0 {}
+   |                    ^
+
+error: unreachable pattern
+  --> $DIR/top-level-alternation.rs:9:15
+   |
+LL |             | 0 => {}
+   |               ^
+
+error: unreachable pattern
+  --> $DIR/top-level-alternation.rs:14:15
+   |
+LL |             | Some(0) => {}
+   |               ^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/top-level-alternation.rs:19:9
+   |
+LL |         (0, 0) => {}
+   |         ^^^^^^
+
+error: unreachable pattern
+  --> $DIR/top-level-alternation.rs:39:9
+   |
+LL |         _ => {}
+   |         ^
+
+error: unreachable pattern
+  --> $DIR/top-level-alternation.rs:43:9
+   |
+LL |         Some(_) => {}
+   |         ^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/top-level-alternation.rs:44:9
+   |
+LL |         None => {}
+   |         ^^^^
+
+error: unreachable pattern
+  --> $DIR/top-level-alternation.rs:49:9
+   |
+LL |         None | Some(_) => {}
+   |         ^^^^^^^^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/top-level-alternation.rs:53:9
+   |
+LL |         1..=2 => {},
+   |         ^^^^^
+
+error: aborting due to 10 previous errors
+