From ea9d2fb85cedcc7e32ab3ada3f539ad5cf974b53 Mon Sep 17 00:00:00 2001
From: Yuki Okushi <jtitor@2k36.org>
Date: Sun, 22 May 2022 16:13:25 +0900
Subject: [PATCH] Add regression test for #91949

---
 .../traits/issue-91949-hangs-on-recursion.rs  | 30 +++++++++++++++++++
 .../issue-91949-hangs-on-recursion.stderr     | 25 ++++++++++++++++
 2 files changed, 55 insertions(+)
 create mode 100644 src/test/ui/traits/issue-91949-hangs-on-recursion.rs
 create mode 100644 src/test/ui/traits/issue-91949-hangs-on-recursion.stderr

diff --git a/src/test/ui/traits/issue-91949-hangs-on-recursion.rs b/src/test/ui/traits/issue-91949-hangs-on-recursion.rs
new file mode 100644
index 0000000000000..cf2218fe52292
--- /dev/null
+++ b/src/test/ui/traits/issue-91949-hangs-on-recursion.rs
@@ -0,0 +1,30 @@
+// build-fail
+// error-pattern: overflow evaluating the requirement `(): Sized`
+// error-pattern: function cannot return without recursing
+
+// Regression test for #91949.
+// This hanged *forever* on 1.56, fixed by #90423.
+
+#![recursion_limit = "256"]
+
+struct Wrapped<T>(T);
+
+struct IteratorOfWrapped<T, I: Iterator<Item = T>>(I);
+
+impl<T, I: Iterator<Item = T>> Iterator for IteratorOfWrapped<T, I> {
+    type Item = Wrapped<T>;
+    fn next(&mut self) -> Option<Wrapped<T>> {
+        self.0.next().map(Wrapped)
+    }
+}
+
+fn recurse<T>(elements: T) -> Vec<char>
+where
+    T: Iterator<Item = ()>,
+{
+    recurse(IteratorOfWrapped(elements).map(|t| t.0))
+}
+
+fn main() {
+    recurse(std::iter::empty());
+}
diff --git a/src/test/ui/traits/issue-91949-hangs-on-recursion.stderr b/src/test/ui/traits/issue-91949-hangs-on-recursion.stderr
new file mode 100644
index 0000000000000..6c04616344f54
--- /dev/null
+++ b/src/test/ui/traits/issue-91949-hangs-on-recursion.stderr
@@ -0,0 +1,25 @@
+warning: function cannot return without recursing
+  --> $DIR/issue-91949-hangs-on-recursion.rs:21:1
+   |
+LL | / fn recurse<T>(elements: T) -> Vec<char>
+LL | | where
+LL | |     T: Iterator<Item = ()>,
+LL | | {
+LL | |     recurse(IteratorOfWrapped(elements).map(|t| t.0))
+   | |     ------------------------------------------------- recursive call site
+LL | | }
+   | |_^ cannot return without recursing
+   |
+   = note: `#[warn(unconditional_recursion)]` on by default
+   = help: a `loop` may express intention better if this is on purpose
+
+error[E0275]: overflow evaluating the requirement `(): Sized`
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "512"]` attribute to your crate (`issue_91949_hangs_on_recursion`)
+   = note: required because of the requirements on the impl of `Iterator` for `std::iter::Empty<()>`
+   = note: 171 redundant requirements hidden
+   = note: required because of the requirements on the impl of `Iterator` for `IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), Map<IteratorOfWrapped<(), std::iter::Empty<()>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>, [closure@$DIR/issue-91949-hangs-on-recursion.rs:25:45: 25:52]>>`
+
+error: aborting due to previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0275`.