louis-e/arnis · error

internal error: entered unreachable code

Error message

internal error: entered unreachable code

What it means

In `generate_leisure`, a `random_choice` value is matched against ranges 0..5, 5..10, 10..16, 16..22, 22..30 to pick a flower/fern block, with `_ => unreachable!()`. The panic means the code produced a `random_choice` outside 0..30, i.e. the value generator and this match table are out of sync (note 0..5/5..10 are exclusive ranges, so 5 and 10 fall through correctly to later arms, but anything >= 30 does not).

Source

Thrown at src/element_processing/leisure.rs:117

                // or path inside the park is drawn after it, so its columns still
                // read as grass here and only the mask tells them apart.
                if matches!(leisure_type.as_str(), "park" | "garden" | "nature_reserve")
                    && editor.check_for_block(x, 0, z, Some(&[GRASS_BLOCK]))
                    && !editor.surface_is_sealed(x, z)
                    && !editor.is_lc_water(x, z)
                {
                    let random_choice: i32 = rng.random_range(0..1000);

                    match random_choice {
                        0..30 => {
                            // Plants
                            let plant_choice = match random_choice {
                                0..5 => RED_FLOWER,
                                5..10 => YELLOW_FLOWER,
                                10..16 => BLUE_FLOWER,
                                16..22 => WHITE_FLOWER,
                                22..30 => FERN,
                                _ => unreachable!(),
                            };
                            editor.set_block(plant_choice, x, 1, z, None, None);
                        }
                        30..90 => {
                            // Grass
                            editor.set_block(GRASS, x, 1, z, None, None);
                        }
                        90..105 => {
                            // Oak leaves
                            editor.set_block(OAK_LEAVES, x, 1, z, None, None);
                        }
                        105..120 => {
                            // Only where land cover says woody, else a park
                            // canopies its own meadows. 1/1000 for specimens.
                            if random_choice == 105 || editor.land_cover_backs_trees(x, z) {
                                Tree::create(
                                    editor,
                                    (x, 1, z),

View on GitHub (pinned to 34048924d9)

Solutions

1. Find where `random_choice` is generated and make its range exactly 0..30 to match the arms
2. Replace `unreachable!()` with a fallback arm (`_ => FERN`) so out-of-range values degrade gracefully
3. Align both the generator range and the match arms in one commit and add a debug_assert for the bound

Example fix

// before
_ => unreachable!(),
// after
_ => FERN, // safe fallback for any out-of-range value
// and upstream: rng.random_range(0..30)

debug_assert!((0..30).contains(&random_choice), "random_choice {random_choice} outside plant table 0..30");

fn in_plant_range(v: i32) -> bool { (0..30).contains(&v) }

When it happens

Trigger: `random_choice` is generated with a range wider than 0..30 upstream (e.g. `rng.random_range(0..100)` or an inclusive upper bound), or the match arms were narrowed without updating the generator.

Common situations: Refactoring the plant distribution tables; changing the RNG range in one place but not the other; copy-pasting a similar match from another generator with different bounds.

Related errors

• Failed to create tile XZBBox
• internal error: entered unreachable code
• provider chain is never empty
• Earth has no PDS raster
• Invalid id

AI-assisted analysis of louis-e/arnis@34048924d9 (2026-09-03). Data as JSON: /api/errors/6eb0ef25faae2630. Report an issue: GitHub.