1 files changed, 135 insertions, 0 deletions
diff --git a/tests/ui/rfc-1445-restrict-constants-in-patterns/fn-ptr-is-structurally-matchable.rs b/tests/ui/rfc-1445-restrict-constants-in-patterns/fn-ptr-is-structurally-matchable.rs
new file mode 100644
index 00000000000..2b3fbd2a4d2
--- /dev/null
+++ b/tests/ui/rfc-1445-restrict-constants-in-patterns/fn-ptr-is-structurally-matchable.rs
@@ -0,0 +1,135 @@
+// run-pass
+
+// This file checks that fn ptrs are considered structurally matchable.
+// See also rust-lang/rust#63479.
+
+fn main() {
+    let mut count = 0;
+
+    // A type which is not structurally matchable:
+    struct NotSM;
+
+    // And one that is:
+    #[derive(PartialEq, Eq)]
+    struct SM;
+
+    fn trivial() {}
+
+    fn sm_to(_: SM) {}
+    fn not_sm_to(_: NotSM) {}
+    fn to_sm() -> SM { SM }
+    fn to_not_sm() -> NotSM { NotSM }
+
+    // To recreate the scenario of interest in #63479, we need to add
+    // a ref-level-of-indirection so that we descend into the type.
+
+    fn r_sm_to(_: &SM) {}
+    fn r_not_sm_to(_: &NotSM) {}
+    fn r_to_r_sm(_: &()) -> &SM { &SM }
+    fn r_to_r_not_sm(_: &()) -> &NotSM { &NotSM }
+
+    #[derive(PartialEq, Eq)]
+    struct Wrap<T>(T);
+
+    // In the code below, we put the match input into a local so that
+    // we can assign it an explicit type that is an fn ptr instead of
+    // a singleton type of the fn itself that the type inference would
+    // otherwise assign.
+
+    // Check that fn() is structural-match
+    const CFN1: Wrap<fn()> = Wrap(trivial);
+    let input: Wrap<fn()> = Wrap(trivial);
+    match Wrap(input) {
+        Wrap(CFN1) => count += 1,
+        Wrap(_) => {}
+    };
+
+    // Check that fn(T) is structural-match when T is too.
+    const CFN2: Wrap<fn(SM)> = Wrap(sm_to);
+    let input: Wrap<fn(SM)> = Wrap(sm_to);
+    match Wrap(input) {
+        Wrap(CFN2) => count += 1,
+        Wrap(_) => {}
+    };
+
+    // Check that fn() -> T is structural-match when T is too.
+    const CFN3: Wrap<fn() -> SM> = Wrap(to_sm);
+    let input: Wrap<fn() -> SM> = Wrap(to_sm);
+    match Wrap(input) {
+        Wrap(CFN3) => count += 1,
+        Wrap(_) => {}
+    };
+
+    // Check that fn(T) is structural-match even if T is not.
+    const CFN4: Wrap<fn(NotSM)> = Wrap(not_sm_to);
+    let input: Wrap<fn(NotSM)> = Wrap(not_sm_to);
+    match Wrap(input) {
+        Wrap(CFN4) => count += 1,
+        Wrap(_) => {}
+    };
+
+    // Check that fn() -> T is structural-match even if T is not.
+    const CFN5: Wrap<fn() -> NotSM> = Wrap(to_not_sm);
+    let input: Wrap<fn() -> NotSM> = Wrap(to_not_sm);
+    match Wrap(input) {
+        Wrap(CFN5) => count += 1,
+        Wrap(_) => {}
+    };
+
+    // Check that fn(&T) is structural-match when T is too.
+    const CFN6: Wrap<fn(&SM)> = Wrap(r_sm_to);
+    let input: Wrap<fn(&SM)> = Wrap(r_sm_to);
+    match Wrap(input) {
+        Wrap(CFN6) => count += 1,
+        Wrap(_) => {}
+    };
+
+    // Check that fn() -> &T is structural-match when T is too.
+    const CFN7: Wrap<fn(&()) -> &SM> = Wrap(r_to_r_sm);
+    let input: Wrap<fn(&()) -> &SM> = Wrap(r_to_r_sm);
+    match Wrap(input) {
+        Wrap(CFN7) => count += 1,
+        Wrap(_) => {}
+    };
+
+    // Check that fn(T) is structural-match even if T is not.
+    const CFN8: Wrap<fn(&NotSM)> = Wrap(r_not_sm_to);
+    let input: Wrap<fn(&NotSM)> = Wrap(r_not_sm_to);
+    match Wrap(input) {
+        Wrap(CFN8) => count += 1,
+        Wrap(_) => {}
+    };
+
+    // Check that fn() -> T is structural-match even if T is not.
+    const CFN9: Wrap<fn(&()) -> &NotSM> = Wrap(r_to_r_not_sm);
+    let input: Wrap<fn(&()) -> &NotSM> = Wrap(r_to_r_not_sm);
+    match Wrap(input) {
+        Wrap(CFN9) => count += 1,
+        Wrap(_) => {}
+    };
+
+    // Check that a type which has fn ptrs is structural-match.
+    #[derive(PartialEq, Eq)]
+    struct Foo {
+        alpha: fn(NotSM),
+        beta: fn() -> NotSM,
+        gamma: fn(SM),
+        delta: fn() -> SM,
+    }
+
+    const CFOO: Foo = Foo {
+        alpha: not_sm_to,
+        beta: to_not_sm,
+        gamma: sm_to,
+        delta: to_sm,
+    };
+
+    let input = Foo { alpha: not_sm_to, beta: to_not_sm, gamma: sm_to, delta: to_sm };
+    match input {
+        CFOO => count += 1,
+        Foo { .. } => {}
+    };
+
+    // Final count must be 10 now if all
+    assert_eq!(count, 10);
+}