Problem with running Benchmarks on substrate pallet: recursion limit reached while expanding `stringify!`

Question

When I add and run a new benchmark via

cargo test --package pallet-<name>  --features runtime-benchmarks

I get an error which is unclear and unrelated to the actual benchmark i added:

error: recursion limit reached while expanding `stringify!`
   --> frame/assets/src/benchmarking.rs:154:1
    |
154 | / benchmarks_instance_pallet! {
155 | |     create {
156 | |         let caller: T::AccountId = whitelisted_caller();
157 | |         let caller_lookup = T::Lookup::unlookup(caller.clone());
...   |
485 | |     impl_benchmark_test_suite!(Assets, crate::mock::new_test_ext(), crate::mock::Test)
486 | | }
    | |_^
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`pallet_assets`)
    = note: this error originates in the macro `$crate::impl_bench_name_tests` which comes from the expansion of the macro `benchmarks_instance_pallet` (in Nightly builds, run with -Z macro-backtrace for more info)

error: could not compile `pallet-assets` due to previous error
warning: build failed, waiting for other jobs to finish...

UPDATE: This is a permalink to the benchmark which I added that lead to this error: https://github.com/paritytech/substrate/blob/2d3b6507817d66f6e2e697074bfc806e4a6eb2a8/frame/assets/src/benchmarking.rs#L180-L180

Answer 1

Looks like you are the first one to find the case where there are too many benchmarks in a file and the macro fails.
This is easily fixed in your case by putting #![recursion_limit = "1024"] at the top of your lib.rs file.
Often these "expansion limit reached" mean that something went wrong, but in this case it's just the large number of benchmarks.