Refactor slice pattern usefulness checking

src/test/ui/pattern/usefulness/slice-patterns.rs

@@ -0,0 +1,96 @@
+#![feature(slice_patterns)]
+#![deny(unreachable_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 s3: &[bool; 3] = &[false; 3];
+
+    let [] = s0;
+    let [_] = s1;
+    let [_, _] = s2;
+
+    let [..] = s;
+    let [..] = s0;
+    let [..] = s1;
+    let [..] = s2;
+    let [..] = s3;
+
+    let [_, _, ..] = s2;
+    let [_, .., _] = s2;
+    let [.., _, _] = s2;
+
+    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 s3 {
+    //~^ ERROR `&[false, _, _]` not covered
+        [true, .., true] => {}
+    }
+    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 {
+        [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] => {}
+        [..] => {}
+    }
+}

src/test/ui/pattern/usefulness/slice-patterns.stderr

@@ -0,0 +1,117 @@
+error[E0004]: non-exhaustive patterns: `&[false, true]` not covered
+  --> $DIR/slice-patterns.rs:29:11
+   |
+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.rs:34:11
+   |
+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.rs:39:11
+   |
+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: `&[false, _, _]` not covered
+  --> $DIR/slice-patterns.rs:46:11
+   |
+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: `&[_]` not covered
+  --> $DIR/slice-patterns.rs:50:11
+   |
+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.rs:54:11
+   |
+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.rs:59:11
+   |
+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.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: `&[_, false]` not covered
+  --> $DIR/slice-patterns.rs:70:11
+   |
+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: unreachable pattern
+  --> $DIR/slice-patterns.rs:79:9
+   |
+LL |         [true, ..] => {}
+   |         ^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/slice-patterns.rs:2:9
+   |
+LL | #![deny(unreachable_patterns)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/slice-patterns.rs:80:9
+   |
+LL |         [true] => {}
+   |         ^^^^^^
+
+error: unreachable pattern
+  --> $DIR/slice-patterns.rs:85:9
+   |
+LL |         [.., true] => {}
+   |         ^^^^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/slice-patterns.rs:86:9
+   |
+LL |         [true] => {}
+   |         ^^^^^^
+
+error: unreachable pattern
+  --> $DIR/slice-patterns.rs:91:9
+   |
+LL |         [false, .., true] => {}
+   |         ^^^^^^^^^^^^^^^^^
+
+error: unreachable pattern
+  --> $DIR/slice-patterns.rs:92:9
+   |
+LL |         [false, true] => {}
+   |         ^^^^^^^^^^^^^
+
+error: aborting due to 15 previous errors
+
+For more information about this error, try `rustc --explain E0004`.