Benchmark promote_fast and others in pallet-core-fellowship Generates Ranks Exceeding MaxRank

[Doordashcon]

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• This is not a support question.

Description of bug

When running the promote_fast benchmark in pallet_core_fellowship, I encountered an issue where the generated rank (r) exceeded the configured MaxRank. Specifically, even when T::MaxRank::get() == 1, the benchmark framework sometimes assigned r = 2, causing the extrinsic call to fail with an InvalidRank error.

Steps to Reproduce

• Configure the runtime with T::MaxRank::get() == 1.
• Run the benchmark for promote_fast.
• Add log::info!("Benchmark promote_fast: r={} MaxRank={}", r, T::MaxRank::get());
• Observe that r is sometimes set to 2, leading to an InvalidRank error.

Expected Behavior
The benchmark framework should respect the constraint that r must be in the range [1, T::MaxRank::get()], ensuring r never exceeds MaxRank.

Actual Behavior
The benchmark framework assigns r = 2 even when MaxRank == 1.
This causes the promote_fast extrinsic to fail validation.

Are you willing to work on this?
yes

cc @ggwpez

[Doordashcon]

This relates to collectives with one rank(i.e. potoc collective)

[ggwpez]

Hm, it should respect it actually.

polkadot-sdk/substrate/frame/core-fellowship/src/benchmarking.rs

Line 217 in 568231a

fn promote_fast(r: Linear<1, { T::MaxRank::get() as u32 }>) -> Result<(), BenchmarkError> {

[Doordashcon]

cargo build -p collectives-polkadot-runtime --features runtime-benchmarks --release

frame-omni-bencher v1 benchmark pallet \
--pallet pallet-core-fellowship --extrinsic "" \
--runtime ./target/release/wbuild/collectives-polkadot-runtime/collectives_polkadot_runtime.compact.compressed.wasm \

2025-02-18T00:35:27.899534Z  INFO pallet_core_fellowship::benchmarking::benchmarks: Benchmark promote_fast: r=1 MaxRank=1    
2025-02-18T00:35:27.900543Z  INFO pallet_core_fellowship::benchmarking::benchmarks: Benchmark promote_fast: r=2 MaxRank=9    
2025-02-18T00:35:27.901147Z  INFO pallet_core_fellowship::benchmarking::benchmarks: Benchmark promote_fast: r=2 MaxRank=9    
2025-02-18T00:35:27.901723Z  INFO pallet_core_fellowship::benchmarking::benchmarks: Benchmark promote_fast: r=2 MaxRank=1

cc @ggwpez