Use env variables or not

[chentong319]

Sometimes I was puzzled by the behavior of some execution or failed to reproduce something because of the hidden env variable. I am wondering whether we should use env variable. If yes, what are the general rules of using env variables in onnx-mlir project?
First of all, I asked someone. Here is the answer:

✅ When It's a Good Approach:

• Configuration Outside of Code:
  Environment variables allow you to control settings without changing code or configuration files. This makes deployment easier, especially in cloud environments (e.g., AWS, Heroku, Docker).

• Sensitive Data Handling:
  Ideal for credentials, API keys, and secrets since they aren't stored in code or version control.

• Cross-Environment Flexibility:
  Useful for configuring behavior across dev, staging, and production environments (e.g., switching databases, toggling debug modes).

• Stateless Applications:
  In containerized environments (like Docker or Kubernetes), environment variables help maintain statelessness by providing configuration at runtime.

❌ When It's Problematic:

• Lack of Visibility:
  If someone runs the program without knowing the necessary environment variables, they may encounter confusing errors.

• Not Always Portable:
  Moving the program between systems can be tricky if the required environment variables aren't documented or set correctly.

• Security Risks:
  If not managed carefully, sensitive data in environment variables can be exposed (e.g., via process lists or misconfigured shells).

• Complexity in Large Projects:
  Heavy reliance on environment variables can lead to "configuration sprawl," making it hard to manage and debug.

I tried to summarize all the uses of env variable in onnx-mlir:

1. Control Cmake: ZDNN_LIBRARY_DIR
2. onnx-mlir execution: IMPORTER_FORCE_DYNAMIC, MallocStackLogging,
3. execution of the compiled model:

• instrumentation: ONNX_MLIR_INSTRUMENT_FILE, ONNX_MLIR_NO_INSTRUMENT_TIME
• NNPA debugging: OM_STATUS_MESSAGES_ENABLED,
• python driver: ONNX_MILR_HOME, MODELS_PATH, PY_LIB, VERBOSE, TEST_NO_FLOAT16, TEST_CASE_BY_USER, and a lot!

What should we do about them and what is the guideline/plan for future?