Feature Request: Conditional Validation for Environment Variables (e.g., RCON Port)

[gOOvER]

This post outlines an observed pattern within multiple Pelican eggs that may benefit from a more systematic and automated solution. During configuration analysis, it became apparent that certain environment variables become logically required only when another variable is set to a specific value. A representative example is the relationship between RCON_ENABLED and RCON_PORT. Although RCON_PORT is defined as nullable, it becomes functionally mandatory when RCON_ENABLED=1.

The idea for this feature emerged while reviewing a Copilot-generated comment in the following discussion:
pelican-eggs/games-standalone#84 (comment)

This behavior is not isolated to a single egg. Similar conditional dependencies appear across various implementations, and the current approach requires manual validation or custom scripting. This introduces potential inconsistencies and increases the likelihood of misconfiguration.

Proposed Enhancement

Introduce a native mechanism within Pelican to define conditional validation rules for environment variables. The following rule formats illustrate the intended concept:

• required_if:VAR_X,value
• forbidden_if:VAR_Y,value
• integer_if:MODE,advanced
• min_if:FEATURE_Z,enabled

These examples demonstrate how conditional logic could be expressed declaratively, allowing Pelican to enforce configuration correctness automatically.

Expected Benefits

• Reduction of configuration errors before runtime
• Lower support overhead for administrators
• Increased clarity and predictability for egg developers
• More consistent validation behavior across the ecosystem
• Removal of ad-hoc scripting solutions

Example Scenario

If RCON_ENABLED=1, then RCON_PORT must contain a valid port number.
If RCON_ENABLED=0, the value of RCON_PORT becomes irrelevant and should not be required.

This pattern appears frequently enough that a built-in solution would provide measurable value to both developers and end users.

[JuggleGaming]

This would be great.