test(criterion_compat): add custom main bench for URI formatting

Covers calling bench functions directly with a custom main, both with and
without going through a criterion_group!-generated function.

Author: not-matthias

crates/criterion_compat/Cargo.toml

@@ -68,3 +68,7 @@ harness = false
 [[bench]]
 name = "test_benches"
 harness = false
+
+[[bench]]
+name = "custom_main"
+harness = false

crates/criterion_compat/benches/custom_main.rs

@@ -0,0 +1,42 @@
+/// Test bench for custom main patterns (COD-2324).
+/// Verifies URI formatting when users bypass criterion_group!/criterion_main!.
+use codspeed_criterion_compat::{criterion_group, BenchmarkId, Criterion};
+
+fn bench_with_group(c: &mut Criterion) {
+    let mut group = c.benchmark_group("my_group");
+    group.bench_function("my_bench", |b| b.iter(|| 2 + 2));
+    group.bench_function(BenchmarkId::new("parameterized", 42), |b| b.iter(|| 2 + 2));
+    group.finish();
+}
+
+criterion_group!(benches, bench_with_group);
+
+#[cfg(codspeed)]
+fn main() {
+    // Pattern A: Using new_instrumented() but calling bench functions directly (not through criterion_group!)
+    // Since criterion_group! is bypassed, there is no macro context (group/function name),
+    // so the URI only contains the file, benchmark group, and benchmark name.
+    //
+    // Expected URIs:
+    // - crates/criterion_compat/benches/custom_main.rs::my_group::my_bench
+    // - crates/criterion_compat/benches/custom_main.rs::my_group::parameterized[42]
+    let mut criterion = Criterion::new_instrumented();
+    bench_with_group(&mut criterion);
+
+    // Pattern B: Calling through criterion_group!-generated function (should work correctly)
+    // The macro captures the criterion_group! name (`benches`) and the bench function name
+    // (`bench_with_group`), so both are part of the URI.
+    //
+    // Expected URIs:
+    // - crates/criterion_compat/benches/custom_main.rs::benches::bench_with_group::my_group::my_bench
+    // - crates/criterion_compat/benches/custom_main.rs::benches::bench_with_group::my_group::parameterized[42]
+    let mut criterion2 = Criterion::new_instrumented();
+    benches(&mut criterion2);
+}
+
+#[cfg(not(codspeed))]
+fn main() {
+    // Without codspeed, just run through upstream criterion directly
+    let mut criterion = Criterion::default().configure_from_args();
+    bench_with_group(&mut criterion);
+}