Infra for "unit" benchmarking

crates/test_utils/src/bench_fixture.rs

@@ -0,0 +1,28 @@
+//! Generates large snippets of Rust code for usage in the benchmarks.
+
+use stdx::format_to;
+
+pub fn big_struct() -> String {
+    let n = 1_000;
+
+    let mut buf = "pub struct RegisterBlock {".to_string();
+    for i in 0..n {
+        format_to!(buf, "  /// Doc comment for {}.\n", i);
+        format_to!(buf, "  pub s{}: S{},\n", i, i);
+    }
+    buf.push_str("}\n\n");
+    for i in 0..n {
+        format_to!(
+            buf,
+            "
+
+#[repr(transparent)]
+struct S{} {{
+    field: u32,
+}}",
+            i
+        );
+    }
+
+    buf
+}