make PhantomData #[structural_match].

src/test/ui/rfc1445/phantom-data-is-structurally-matchable.rs

@@ -0,0 +1,53 @@
+// run-pass
+
+// This file checks that `PhantomData` is considered structurally matchable.
+
+use std::marker::PhantomData;
+
+fn main() {
+    let mut count = 0;
+
+    // A type which is not structurally matchable:
+    struct NotSM;
+
+    // And one that is:
+    #[derive(PartialEq, Eq)]
+    struct SM;
+
+    // Check that SM is #[structural_match]:
+    const CSM: SM = SM;
+    match SM {
+        CSM => count += 1,
+    };
+
+    // Check that PhantomData<T> is #[structural_match] even if T is not.
+    const CPD1: PhantomData<NotSM> = PhantomData;
+    match PhantomData {
+        CPD1 => count += 1,
+    };
+
+    // Check that PhantomData<T> is #[structural_match] when T is.
+    const CPD2: PhantomData<SM> = PhantomData;
+    match PhantomData {
+        CPD2 => count += 1,
+    };
+
+    // Check that a type which has a PhantomData is `#[structural_match]`.
+    #[derive(PartialEq, Eq, Default)]
+    struct Foo {
+        alpha: PhantomData<NotSM>,
+        beta: PhantomData<SM>,
+    }
+
+    const CFOO: Foo = Foo {
+        alpha: PhantomData,
+        beta: PhantomData,
+    };
+
+    match Foo::default() {
+        CFOO => count += 1,
+    };
+
+    // Final count must be 4 now if all
+    assert_eq!(count, 4);
+}