Add token-stream-stress benchmark.

collector/benchmarks/README.md

@@ -81,6 +81,9 @@ programs.
   performance](https://github.com/rust-lang/rust/issues/46449) in the past.
 - **regression-31157**: A small program that caused a [large performance
   regression](https://github.com/rust-lang/rust/issues/31157) from the past.
+- **token-stream-stress**: Constructs a long token stream much like the `quote`
+  crate does, which caused [quadratic
+  behavior](https://github.com/rust-lang/rust/issues/65080) in the past.
 - **tuple-stress**: Contains a single array of 65,535 nested `(i32, (f64, f64,
   f64))` tuples. The data was extracted and reduced from a [program dealing
   with grid coordinates](https://github.com/urschrei/ostn15_phf) that was

collector/benchmarks/token-stream-stress/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "token-stream-stress"
+version = "0.0.0"
+edition = "2018"
+publish = false
+
+[lib]
+path = "src/lib.rs"
+proc-macro = true
+
+[[bin]]
+name = "token-stream-stress"
+path = "src/main.rs"

collector/benchmarks/token-stream-stress/perf-config.json

@@ -0,0 +1,3 @@
+{
+    "cargo_opts": "--bin token-stream-stress"
+}

collector/benchmarks/token-stream-stress/src/lib.rs

@@ -0,0 +1,28 @@
+extern crate proc_macro;
+
+use proc_macro::{Ident, Punct, Spacing, Span, TokenStream, TokenTree};
+use std::iter::once;
+
+const N: u32 = 2000;
+
+#[proc_macro]
+pub fn bench(_input: TokenStream) -> TokenStream {
+    let span = Span::call_site();
+    let mut tokens = TokenStream::new();
+    for _ in 0..N {
+        // Similar to what is emitted by `quote`.
+        tokens.extend(once(TokenTree::Ident(Ident::new("core", span))));
+        tokens.extend(once(TokenTree::Punct(Punct::new(':', Spacing::Joint))));
+        tokens.extend(once(TokenTree::Punct(Punct::new(':', Spacing::Alone))));
+        tokens.extend(once(TokenTree::Ident(Ident::new("option", span))));
+        tokens.extend(once(TokenTree::Punct(Punct::new(':', Spacing::Joint))));
+        tokens.extend(once(TokenTree::Punct(Punct::new(':', Spacing::Alone))));
+        tokens.extend(once(TokenTree::Ident(Ident::new("Option", span))));
+        tokens.extend(once(TokenTree::Punct(Punct::new(':', Spacing::Joint))));
+        tokens.extend(once(TokenTree::Punct(Punct::new(':', Spacing::Alone))));
+        tokens.extend(once(TokenTree::Ident(Ident::new("None", span))));
+        tokens.extend(once(TokenTree::Punct(Punct::new(',', Spacing::Joint))));
+    }
+
+    TokenStream::new()
+}

collector/benchmarks/token-stream-stress/src/main.rs

@@ -0,0 +1,3 @@
+token_stream_stress::bench!();
+
+fn main() {}