mirror of https://github.com/rust-lang/rust
39 lines
1.2 KiB
Rust
39 lines
1.2 KiB
Rust
// Demonstrate that a type param in negative position causes dropck to reject code
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// that might indirectly access previously dropped value.
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//
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// Compare with run-pass/issue28498-ugeh-with-passed-to-fn.rs
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#[derive(Debug)]
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struct ScribbleOnDrop(String);
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impl Drop for ScribbleOnDrop {
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fn drop(&mut self) {
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self.0 = format!("DROPPED");
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}
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}
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struct Foo<T>(u32, T, Box<for <'r> fn(&'r T) -> String>);
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impl<T> Drop for Foo<T> {
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fn drop(&mut self) {
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// Use of `may_dangle` is unsound, because we pass `T` to the callback in `self.2`
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// below, and thus potentially read from borrowed data.
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println!("Dropping Foo({}, {})", self.0, (self.2)(&self.1));
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}
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}
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fn callback(s: & &ScribbleOnDrop) -> String { format!("{:?}", s) }
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fn main() {
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let (last_dropped, foo0);
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let (foo1, first_dropped);
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last_dropped = ScribbleOnDrop(format!("last"));
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first_dropped = ScribbleOnDrop(format!("first"));
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foo0 = Foo(0, &last_dropped, Box::new(callback)); // OK
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foo1 = Foo(1, &first_dropped, Box::new(callback));
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//~^ ERROR `first_dropped` does not live long enough
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println!("foo0.1: {:?} foo1.1: {:?}", foo0.1, foo1.1);
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}
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