rollup merge of #23486: nikomatsakis/issue-23485

When testing whether a default method predicates are satisfiable,
combine normalization with this check so that we also skip the
default method if normalization fails. Fixes #23485.

r? @nrc (I tried to address your nit from before as well)

1 files changed, 58 insertions, 0 deletions

diff --git a/src/test/run-pass/issue-23485.rs b/src/test/run-pass/issue-23485.rs
new file mode 100644
index 00000000000..aad410c4abf
--- /dev/null
+++ b/src/test/run-pass/issue-23485.rs
@@ -0,0 +1,58 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test for an ICE that occured when a default method implementation
+// was applied to a type that did not meet the prerequisites. The
+// problem occurred specifically because normalizing
+// `Self::Item::Target` was impossible in this case.
+
+use std::boxed::Box;
+use std::marker::Sized;
+use std::clone::Clone;
+use std::ops::Deref;
+use std::option::Option;
+use std::option::Option::{Some,None};
+
+trait Iterator {
+    type Item;
+
+    fn next(&mut self) -> Option<Self::Item>;
+
+    fn clone_first(mut self) -> Option<<Self::Item as Deref>::Target> where
+        Self: Sized,
+        Self::Item: Deref,
+        <Self::Item as Deref>::Target: Clone,
+    {
+        self.next().cloned()
+    }
+}
+
+struct Counter {
+    value: i32
+}
+
+struct Token {
+    value: i32
+}
+
+impl Iterator for Counter {
+    type Item = Token;
+
+    fn next(&mut self) -> Option<Token> {
+        let x = self.value;
+        self.value += 1;
+        Some(Token { value: x })
+    }
+}
+
+fn main() {
+    let mut x: Box<Iterator<Item=Token>> = Box::new(Counter { value: 22 });
+    assert_eq!(x.next().unwrap().value, 22);
+}