Add tests

Author: Nadrieril

src/test/ui/pattern/usefulness/const-private-fields.rs

@@ -0,0 +1,30 @@
+// check-pass
+//
+// Check that we don't ignore private fields in usefulness checking
+#![deny(unreachable_patterns)]
+
+mod inner {
+    #[derive(PartialEq, Eq)]
+    pub struct PrivateField {
+        pub x: bool,
+        y: bool,
+    }
+
+    pub const FOO: PrivateField = PrivateField { x: true, y: true };
+    pub const BAR: PrivateField = PrivateField { x: true, y: false };
+}
+use inner::*;
+
+fn main() {
+    match FOO {
+        FOO => {}
+        BAR => {}
+        _ => {}
+    }
+
+    match FOO {
+        FOO => {}
+        PrivateField { x: true, .. } => {}
+        _ => {}
+    }
+}

src/test/ui/pattern/usefulness/issue-82772-match-box-as-struct.rs

@@ -0,0 +1,6 @@
+// This used to ICE in exhaustiveness checking. Explanation here:
+// https://github.com/rust-lang/rust/issues/82772#issuecomment-905946768
+fn main() {
+    let Box { 1: _, .. }: Box<()>; //~ ERROR field `1` of
+    let Box { .. }: Box<()>;
+}

src/test/ui/pattern/usefulness/issue-82772-match-box-as-struct.stderr

@@ -0,0 +1,9 @@
+error[E0451]: field `1` of struct `Box` is private
+  --> $DIR/issue-82772-match-box-as-struct.rs:4:15
+   |
+LL |     let Box { 1: _, .. }: Box<()>;
+   |               ^^^^ private field
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0451`.