use overflow::OverflowData;
use rustc_index::vec::IndexVec;
use rustc_middle::ty::TyCtxt;
-use std::collections::hash_map::Entry;
+use std::{collections::hash_map::Entry, mem};
rustc_index::newtype_index! {
pub struct StackDepth {}
let provisional_entry_index = *cache.lookup_table.get(&goal).unwrap();
let provisional_entry = &mut cache.entries[provisional_entry_index];
let depth = provisional_entry.depth;
+ // We eagerly update the response in the cache here. If we have to reevaluate
+ // this goal we use the new response when hitting a cycle, and we definitely
+ // want to access the final response whenever we look at the cache.
+ let prev_response = mem::replace(&mut provisional_entry.response, response);
+
// Was the current goal the root of a cycle and was the provisional response
// different from the final one.
- if has_been_used && provisional_entry.response != response {
- // If so, update the provisional reponse for this goal...
- provisional_entry.response = response;
- // ...remove all entries whose result depends on this goal
+ if has_been_used && prev_response != response {
+ // If so, remove all entries whose result depends on this goal
// from the provisional cache...
//
// That's not completely correct, as a nested goal can also
--- /dev/null
+// known-bug: unknown
+// compile-flags: -Ztrait-solver=next
+// failure-status: 101
+// normalize-stderr-test "note: .*\n\n" -> ""
+// normalize-stderr-test "thread 'rustc' panicked.*\n" -> ""
+// rustc-env:RUST_BACKTRACE=0
+
+// This tests checks that we update results in the provisional cache when
+// we pop a goal from the stack.
+#![feature(auto_traits)]
+auto trait Coinductive {}
+struct Foo<T>(T);
+struct Bar<T>(T);
+
+impl<T> Coinductive for Foo<T>
+where
+ Bar<T>: Coinductive
+{}
+
+impl<T> Coinductive for Bar<T>
+where
+ Foo<T>: Coinductive,
+ Bar<T>: ConstrainInfer,
+{}
+
+trait ConstrainInfer {}
+impl ConstrainInfer for Bar<u8> {}
+impl ConstrainInfer for Foo<u16> {}
+
+fn impls<T: Coinductive>() -> T { todo!() }
+
+fn constrain<T: ConstrainInfer>(_: T) {}
+
+fn main() {
+ // This should constrain `_` to `u8`.
+ impls::<Foo<_>>();
+}
--- /dev/null
+error: the compiler unexpectedly panicked. this is a bug.
+
+query stack during panic:
+#0 [check_well_formed] checking that `<impl at $DIR/provisional-result-done.rs:20:1: 20:31>` is well-formed
+#1 [check_mod_type_wf] checking that types are well-formed in top-level module
+end of query stack