mirror of https://github.com/rust-lang/rust
51 lines
1.3 KiB
Rust
51 lines
1.3 KiB
Rust
// Test where we might in theory be able to see that the relationship
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// between two bound regions is true within closure and hence have no
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// need to propagate; but in fact we do because identity of free
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// regions is erased.
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//@ compile-flags:-Zverbose-internals
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//@ check-pass
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#![feature(rustc_attrs)]
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use std::cell::Cell;
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// In theory, callee knows that:
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//
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// 'x: 'a
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// 'a: 'y
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//
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// and hence could satisfy that `'x: 'y` locally. However, in our
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// checking, we ignore the precise free regions that come into the
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// region and just assign each position a distinct universally bound
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// region. Hence, we propagate a constraint to our caller that will
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// wind up being solvable.
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fn establish_relationships<'a, F>(
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_cell_a: Cell<&'a u32>,
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_closure: F,
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) where
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F: for<'x, 'y> FnMut(
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Cell<&'a &'x u32>, // shows that 'x: 'a
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Cell<&'y &'a u32>, // shows that 'a: 'y
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Cell<&'x u32>,
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Cell<&'y u32>,
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),
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{
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}
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fn demand_y<'x, 'y>(_cell_x: Cell<&'x u32>, _cell_y: Cell<&'y u32>, _y: &'y u32) {}
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#[rustc_regions]
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fn supply<'a>(cell_a: Cell<&'a u32>) {
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establish_relationships(
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cell_a,
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|_outlives1, _outlives2, x, y| {
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// Only works if 'x: 'y:
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let p = x.get();
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demand_y(x, y, p)
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},
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);
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}
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fn main() {}
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