Add benchmark for deeply nested types

collector/benchmarks/deeply-nested/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "deeply-nested"
+version = "0.1.0"
+authors = ["Tatsuyuki Ishi <ishitatsuyuki@gmail.com>"]
+
+[dependencies]

collector/benchmarks/deeply-nested/src/lib.rs

@@ -0,0 +1,26 @@
+// A test case from rust-lang/rust#38528.
+// The original blowup had both exponential compute and memory complexity.
+// The nesting should be kept at 16 level to avoid crashing the test machine.
+
+pub fn foo() -> Box<Iterator<Item = ()>> {
+    use std::iter::empty;
+
+    Box::new(empty()
+        .chain(empty())
+        .chain(empty())
+        .chain(empty())
+        .chain(empty())
+        .chain(empty())
+        .chain(empty())
+        .chain(empty())
+        .chain(empty())
+        .chain(empty())
+        .chain(empty()) // 10th .chain(empty())
+        .chain(empty())
+        .chain(empty())
+        .chain(empty())
+        .chain(empty())
+        .chain(empty())
+        .chain(empty()) // 16th .chain(empty())
+    )
+}