83 lines
2.1 KiB
Rust
83 lines
2.1 KiB
Rust
// Test that we can propagate `T: 'a` obligations to our caller. See
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// `correct_region` for an explanation of how this test is setup; it's
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// somewhat intricate.
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// compile-flags:-Zverbose
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#![allow(warnings)]
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#![feature(rustc_attrs)]
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use std::cell::Cell;
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fn with_signature<'a, T, F>(a: Cell<&'a ()>, b: T, op: F)
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where
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F: FnOnce(Cell<&'a ()>, T),
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{
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op(a, b)
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}
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fn require<'a, T>(_a: &Cell<&'a ()>, _b: &T)
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where
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T: 'a,
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{
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}
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#[rustc_regions]
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fn no_region<'a, T>(a: Cell<&'a ()>, b: T) {
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with_signature(a, b, |x, y| {
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// See `correct_region`, which explains the point of this
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// test. The only difference is that, in the case of this
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// function, there is no where clause *anywhere*, and hence we
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// get an error (but reported by the closure creator).
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require(&x, &y)
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//~^ ERROR the parameter type `T` may not live long enough
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})
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}
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#[rustc_regions]
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fn correct_region<'a, T>(a: Cell<&'a ()>, b: T)
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where
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T: 'a,
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{
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with_signature(a, b, |x, y| {
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// Key point of this test:
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//
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// The *closure* is being type-checked with all of its free
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// regions "universalized". In particular, it does not know
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// that `x` has the type `Cell<&'a ()>`, but rather treats it
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// as if the type of `x` is `Cell<&'A ()>`, where `'A` is some
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// fresh, independent region distinct from the `'a` which
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// appears in the environment. The call to `require` here
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// forces us then to prove that `T: 'A`, but the closure
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// cannot do it on its own. It has to surface this requirement
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// to its creator (which knows that `'a == 'A`).
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require(&x, &y)
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})
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}
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#[rustc_regions]
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fn wrong_region<'a, 'b, T>(a: Cell<&'a ()>, b: T)
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where
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T: 'b,
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{
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with_signature(a, b, |x, y| {
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// See `correct_region`
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require(&x, &y)
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//~^ ERROR the parameter type `T` may not live long enough
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})
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}
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#[rustc_regions]
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fn outlives_region<'a, 'b, T>(a: Cell<&'a ()>, b: T)
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where
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T: 'b,
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'b: 'a,
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{
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with_signature(a, b, |x, y| {
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// See `correct_region`
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require(&x, &y)
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})
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}
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fn main() {}
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