Add test for issue-50900

Author: JohnTitor

Diff for: src/test/ui/issues/issue-50900.rs

@@ -0,0 +1,19 @@
+#[derive(PartialEq, Eq)]
+pub struct Tag(pub Context, pub u16);
+
+#[derive(PartialEq, Eq)]
+pub enum Context {
+    Tiff,
+    Exif,
+}
+
+impl Tag {
+    const ExifIFDPointer: Tag = Tag(Context::Tiff, 34665);
+}
+
+fn main() {
+    match Tag::ExifIFDPointer {
+    //~^ ERROR: non-exhaustive patterns: `Tag(Exif, _)` not covered
+        Tag::ExifIFDPointer => {}
+    }
+}

Diff for: src/test/ui/issues/issue-50900.stderr

@@ -0,0 +1,14 @@
+error[E0004]: non-exhaustive patterns: `Tag(Exif, _)` not covered
+  --> $DIR/issue-50900.rs:15:11
+   |
+LL | pub struct Tag(pub Context, pub u16);
+   | ------------------------------------- `Tag` defined here
+...
+LL |     match Tag::ExifIFDPointer {
+   |           ^^^^^^^^^^^^^^^^^^^ pattern `Tag(Exif, _)` not covered
+   |
+   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0004`.