Add a few more tests of edge cases

Author: oli-obk

Diff for: src/test/ui/pattern/slice-pattern-const-2.rs

@@ -21,4 +21,11 @@ fn main() {
         MAGIC_TEST => (), // this should warn
         _ => (),
     }
+    const FOO: [u32; 1] = [4];
+    match [99] {
+        [0x00] => (),
+        [4] => (),
+        FOO => (), // this should warn
+        _ => (),
+    }
 }

Diff for: src/test/ui/pattern/slice-pattern-const-3.rs

@@ -21,4 +21,11 @@ fn main() {
         MAGIC_TEST => (), // this should warn
         _ => (),
     }
+    const FOO: [&str; 1] = ["boo"];
+    match ["baa"] {
+        ["0x00"] => (),
+        ["boo"] => (),
+        FOO => (), // this should warn
+        _ => (),
+    }
 }

Diff for: src/test/ui/pattern/slice-pattern-const.rs

@@ -21,4 +21,27 @@ fn main() {
         MAGIC_TEST => (), // this should warn
         _ => (),
     }
+    const FOO: [u8; 1] = [4];
+    match [99] {
+        [0x00] => (),
+        [4] => (),
+        FOO => (), // this should warn
+        _ => (),
+    }
+    const BAR: &[u8; 1] = &[4];
+    match &[99] {
+        [0x00] => (),
+        [4] => (),
+        BAR => (), // this should warn
+        b"a" => (),
+        _ => (),
+    }
+
+    const BOO: &[u8; 0] = &[];
+    match &[] {
+        [] => (),
+        BOO => (), // this should warn
+        b"" => (),
+        _ => (),
+    }
 }