rust/tests/ui/drop/field-replace-in-struct-with-drop.rs

//! Circa 2016-06-05, `fn inline` below issued an
//! erroneous warning from the elaborate_drops pass about moving out of
//! a field in `Foo`, which has a destructor (and thus cannot have
//! content moved out of it). The reason that the warning is erroneous
//! in this case is that we are doing a *replace*, not a move, of the
//! content in question, and it is okay to replace fields within `Foo`.
//!
//! Another more subtle problem was that the elaborate_drops was
//! creating a separate drop flag for that internally replaced content,
//! even though the compiler should enforce an invariant that any drop
//! flag for such subcontent of `Foo` will always have the same value
//! as the drop flag for `Foo` itself.
//!
//! Regression test for <https://github.com/rust-lang/rust/issues/34101>.

//@ check-pass

struct Foo(String);

impl Drop for Foo {
    fn drop(&mut self) {}
}

fn test_inline_replacement() {
    // dummy variable so `f` gets assigned `var1` in MIR for both functions
    let _s = ();
    let mut f = Foo(String::from("foo"));
    f.0 = String::from("bar"); // This should not warn
}

fn test_outline_replacement() {
    let _s = String::from("foo");
    let mut f = Foo(_s);
    f.0 = String::from("bar"); // This should not warn either
}

fn main() {
    test_inline_replacement();
    test_outline_replacement();
}