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-rw-r--r--tests/ui/nll/ty-outlives/ty-param-closure-outlives-from-where-clause.rs82
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diff --git a/tests/ui/nll/ty-outlives/ty-param-closure-outlives-from-where-clause.rs b/tests/ui/nll/ty-outlives/ty-param-closure-outlives-from-where-clause.rs
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+++ b/tests/ui/nll/ty-outlives/ty-param-closure-outlives-from-where-clause.rs
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+// Test that we can propagate `T: 'a` obligations to our caller. See
+// `correct_region` for an explanation of how this test is setup; it's
+// somewhat intricate.
+
+// compile-flags:-Zverbose
+
+#![allow(warnings)]
+#![feature(rustc_attrs)]
+
+use std::cell::Cell;
+
+fn with_signature<'a, T, F>(a: Cell<&'a ()>, b: T, op: F)
+where
+ F: FnOnce(Cell<&'a ()>, T),
+{
+ op(a, b)
+}
+
+fn require<'a, T>(_a: &Cell<&'a ()>, _b: &T)
+where
+ T: 'a,
+{
+}
+
+#[rustc_regions]
+fn no_region<'a, T>(a: Cell<&'a ()>, b: T) {
+ with_signature(a, b, |x, y| {
+ // See `correct_region`, which explains the point of this
+ // test. The only difference is that, in the case of this
+ // function, there is no where clause *anywhere*, and hence we
+ // get an error (but reported by the closure creator).
+ require(&x, &y)
+ //~^ ERROR the parameter type `T` may not live long enough
+ })
+}
+
+#[rustc_regions]
+fn correct_region<'a, T>(a: Cell<&'a ()>, b: T)
+where
+ T: 'a,
+{
+ with_signature(a, b, |x, y| {
+ // Key point of this test:
+ //
+ // The *closure* is being type-checked with all of its free
+ // regions "universalized". In particular, it does not know
+ // that `x` has the type `Cell<&'a ()>`, but rather treats it
+ // as if the type of `x` is `Cell<&'A ()>`, where `'A` is some
+ // fresh, independent region distinct from the `'a` which
+ // appears in the environment. The call to `require` here
+ // forces us then to prove that `T: 'A`, but the closure
+ // cannot do it on its own. It has to surface this requirement
+ // to its creator (which knows that `'a == 'A`).
+ require(&x, &y)
+ })
+}
+
+#[rustc_regions]
+fn wrong_region<'a, 'b, T>(a: Cell<&'a ()>, b: T)
+where
+ T: 'b,
+{
+ with_signature(a, b, |x, y| {
+ // See `correct_region`
+ require(&x, &y)
+ //~^ ERROR the parameter type `T` may not live long enough
+ })
+}
+
+#[rustc_regions]
+fn outlives_region<'a, 'b, T>(a: Cell<&'a ()>, b: T)
+where
+ T: 'b,
+ 'b: 'a,
+{
+ with_signature(a, b, |x, y| {
+ // See `correct_region`
+ require(&x, &y)
+ })
+}
+
+fn main() {}