c_code_documentation

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Best practices for AI agents documenting the GnollHack C codebase. Covers file headers, function documentation, inline comments, macro explanations, and strategies for making legacy NetHack-derived C code understandable to modern developers.

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C Code Documentation

Critical Rules

Never delete existing documentation. Append to or clarify existing comments; do not replace them.
Use /* */ for all C comments. Do NOT use // in the C core.
Document game mechanics, not syntax. Explain why the code does what it does in the context of the game.

Documentation Standards

File Headers

Add a top-level block comment explaining the file's purpose within the game engine.

/*
 * file.c — Description of the subsystem.
 * Explains how this file connects to other parts of the engine.
 */

Function Documentation

Place a block comment above the function definition (not the prototype).

/*
 * function_name()
 *
 * Describe what the function does, what the parameters mean,
 * and what it returns. Mention any side effects (e.g., "might
 * destroy the object" or "can kill the player").
 */

Inline Comments

Use inline comments for complex bitwise operations, obscure macros, or deeply nested logic.

if (u.umonnum == PM_LICH) {
    /* Liches are immune to cold damage */
    ...
}

Macros

Document complex macros with a block comment explaining the pattern and usage.

Common Idioms to Document

rn2(n): Returns a random integer 0 to n-1.
d(n, s): Rolls n dice with s sides.
Obj_gone_p(otmp): Checks if an object has been freed.
Iterating over fmon (monster list): Always document that nmon must be saved before processing in case the monster dies.