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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-30 03:57:31 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-30 03:57:31 +0000
commitdc0db358abe19481e475e10c32149b53370f1a1c (patch)
treeab8ce99c4b255ce46f99ef402c27916055b899ee /tests/ui/higher-ranked/trait-bounds/hrtb-exists-forall-trait-invariant.rs
parentReleasing progress-linux version 1.71.1+dfsg1-2~progress7.99u1. (diff)
downloadrustc-dc0db358abe19481e475e10c32149b53370f1a1c.tar.xz
rustc-dc0db358abe19481e475e10c32149b53370f1a1c.zip
Merging upstream version 1.72.1+dfsg1.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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diff --git a/tests/ui/higher-ranked/trait-bounds/hrtb-exists-forall-trait-invariant.rs b/tests/ui/higher-ranked/trait-bounds/hrtb-exists-forall-trait-invariant.rs
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+// Test an `exists<'a> { forall<'b> { 'a = 'b } }` pattern -- which should not compile!
+//
+// In particular, we test this pattern in trait solving, where it is not connected
+// to any part of the source code.
+
+use std::cell::Cell;
+
+trait Trait<T> {}
+
+fn foo<T>()
+where
+ T: Trait<for<'b> fn(Cell<&'b u32>)>,
+{
+}
+
+impl<'a> Trait<fn(Cell<&'a u32>)> for () {}
+
+fn main() {
+ // Here, proving that `(): Trait<for<'b> fn(&'b u32)>` uses the impl:
+ //
+ // - The impl provides the clause `forall<'a> { (): Trait<fn(&'a u32)> }`
+ // - We instantiate `'a` existentially to get `(): Trait<fn(&?a u32)>`
+ // - We unify `fn(&?a u32)` with `for<'b> fn(&'b u32)`
+ // - This requires (among other things) instantiating `'b` universally,
+ // yielding `fn(&!b u32)`, in a fresh universe U1
+ // - So we get `?a = !b` but the universe U0 assigned to `?a` cannot name `!b`.
+
+ foo::<()>(); //~ ERROR implementation of `Trait` is not general enough
+}