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CONTRIBUTING.md

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Contributing

Axiom is a set of composable libraries for Compute frontend in the Velox ecosystem. Please refer to the contribution guidelines here

CMake guidelines

There are 4 top-level libraries in Axiom. Each of them is a separate CMake target.

  • optimizer
  • runner
  • logical_plan
  • connectors

Connectors library is special as it inludes a set of plugins / connectors. Each of the connectors is a separate CMake target.

  • connectors/tpch
  • connectors/hive

Avoid introducing new CMake targets unless there is a clear reason to do so.

Design guidelines

Keep Axiom generic

Axiom is designed to work with different SQL dialects, not just Presto. Avoid hard-coding function names, type names, or dialect-specific behavior directly in the optimizer or runner. Instead, use the FunctionRegistry to register well-known functions by their semantic role and look them up at optimization time.

// ❌ Wrong — hard-coded function name.
if (name == "row_number") {
  return RankFunction::kRowNumber;
}

// ✅ Correct — use registered name from FunctionRegistry.
const auto* registry = FunctionRegistry::instance();
if (registry->rowNumber().has_value() && name == *registry->rowNumber()) {
  return RankFunction::kRowNumber;
}

When adding a new optimization that depends on recognizing a specific function, add a registration method to FunctionRegistry (e.g., registerRowNumber) and register the function in registerPrestoFunctions (or the equivalent for other dialects). This ensures the optimization works regardless of the function name used by a particular dialect.