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The SCCs of the region graph are not a reliable heuristic to use for blaming an interesting constraint for diagnostics. For region errors, if the outlived region is `'static`, or the involved types are invariant in their lifetiems, there will be cycles in the constraint graph containing both the target region and the most interesting constraints to blame. To get better diagnostics in these cases, this commit removes that heuristic.
40 lines
1.1 KiB
Rust
40 lines
1.1 KiB
Rust
// Test a case where we are trying to prove `'x: 'y` and are forced to
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// approximate the shorter end-point (`'y`) to with `'static`. This is
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// because `'y` is higher-ranked but we know of no relations to other
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// regions. Note that `'static` shows up in the stderr output as `'0`.
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//@ compile-flags:-Zverbose-internals
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#![feature(rustc_attrs)]
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use std::cell::Cell;
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// Callee knows that:
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//
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// 'x: 'a
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//
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// so the only way we can ensure that `'x: 'y` is to show that
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// `'a: 'static`.
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fn establish_relationships<'a, 'b, F>(_cell_a: &Cell<&'a u32>, _cell_b: &Cell<&'b u32>, _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<&'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, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
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establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
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// Only works if 'x: 'y:
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demand_y(x, y, x.get())
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//~^ ERROR borrowed data escapes outside of function
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});
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}
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fn main() {}
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