Namespaces¶

TL;DR

Every Lost Cities asset has a full name, namespace:path. Leave the namespace off when referencing something and the mod reads it as lostcities:. A reference that lands in a namespace where nothing is registered does not fall back and does not pass quietly: it throws, and where the throw lands decides whether you lose one chunk or the whole server. game test code review

Every claim on this page carries a chip saying how it was checked. Follow the chip for the evidence.

What a name is¶

An asset name is a resource location, namespace:path. code review

minecraft:stone
lostcities:standard (the built-in world style)
apocalypse:wasteland_city (a custom world style in your own namespace) code review

File location decides the name. The folder right after data/ is the namespace, so a file at data/apocalypse/lostcities/worldstyles/wasteland_city.json registers as apocalypse:wasteland_city. game test code review

The exact folder layout¶

Lost Cities assets are datapack registries, so the path is always the same four segments. code review

data/<your namespace>/lostcities/<asset type>/<name>.json
     └── becomes the      └── fixed, this is  └── buildings, parts, palettes,
         namespace            the registry's      citystyles, worldstyles,
                              own namespace       styles, variants, conditions,
                                                  multibuildings, scattered,
                                                  stuff, predefinedcities,
                                                  predefinedspheres

The lostcities in the middle is not your namespace, it is part of the registry's identity, and it is there no matter whose pack the file is in. That is why the mod's own files sit at data/lostcities/lostcities/parts/...: the first lostcities is the pack, the second is the registry. Only the mod's own files get that doubled-up look. Yours will not. game test code review

A bare name means `lostcities:`¶

Anywhere the mod expects a name (a profile's worldStyle key, a world style's list of city styles, a building's refpalette, and so on), the string is turned into a resource location by one rule: if it contains a colon it is parsed as written, and if it does not, the namespace becomes lostcities. There is no search across namespaces and no fallback to the pack the file came from. code review game test

Reads as lostcities:wasteland_city, whatever pack the file is in

{
  "worldStyle": "wasteland_city"
}

Reads as apocalypse:wasteland_city

{
  "worldStyle": "apocalypse:wasteland_city"
}

Rule of thumb: a file under data/lostcities/... can be referenced bare. A file under data/<your namespace>/... needs that namespace everywhere it is referenced. code review

What a reference into the wrong namespace actually does¶

It throws. Every lookup, including the ones whose method name suggests otherwise, ends in the same place: the registry is asked for the name, returns nothing, and the asset constructor is handed that nothing and fails. code review game test

java.lang.RuntimeException: Error getting resource lostcities:wasteland_city!
Caused by: java.lang.NullPointerException: Cannot invoke
    "mcjty.lostcities.worldgen.lost.regassets.WorldStyleRE.getRegistryName()"
    because "object" is null

What you see depends only on when the reference is first needed. game test

Reference	First read	Result
A profile's `worldStyle`	Building the dimension, before any chunk exists	Server crash on the first chunk generated, reported as `Feature placement` game test
A part name in a building's `parts`	The floor loop, every time that building is considered	Chunks around the building fail and generate empty, logged as `Error generating chunk` game test
A building's or part's `refpalette`	On 7.4.12 and 8.2.2, only when a character has to be resolved out of that palette. On 6.0.3, and from 7.5, always	On 7.4.12 and 8.2.2 nothing at all, and the building still generates, if every part carries its own palette. Elsewhere the building fails game test game test game test

That last row is the one that costs an evening, and only on 7.4.12 and 8.2.2. There, a bare refpalette on a building whose parts each declare their own generated a complete, correct tower, and surfaced only as two unrelated-looking chunk failures elsewhere in the city. Give the same building a part with no palette of its own and it disappears. game test game test

7.5 and later resolve the palette either way, and so did 6.0.3

The same pack on 7.5.1 and on 9.5.1 loses the building entirely and fails eight chunks, including the building's own, instead of two unrelated ones. The mistake became visible instead of invisible. A pack that looked correct on 7.4.12 because of this can stop generating that building on 7.5. game test

6.0.3 resolves it eagerly too, two major versions before 7.5, and has no catch around chunk generation, so there it ends the server rather than losing one building. game test game test

The message names the resolved name, not what you typed

Error getting resource lostcities:wasteland_city! is what a missing namespace looks like. A lostcities: prefix in front of an asset that is not the mod's own means the reference that produced it was written bare. game test

A worked example¶

A profile is a config file, not a datapack file, so it has no namespace of its own. It is named by its file name and it lives outside data/ entirely. The worldStyle value inside it is the point where config crosses into datapack space, and that value is a namespaced reference. code review

Two separate places, one reference between them

config/lostcities/profiles/apocalypse.json
└── the profile is named after its file name: "apocalypse"

<world>/datapacks/apocalypse-pack/
├── pack.mcmeta
└── data/apocalypse/lostcities/
         │           └── the registry, fixed
         └── the namespace, yours to choose
    ├── worldstyles/wasteland.json    registers as apocalypse:wasteland
    └── citystyles/downtown.json      registers as apocalypse:downtown

config/lostcities/profiles/apocalypse.json

{
  "lostcity": {
    "worldStyle": "apocalypse:wasteland"
  }
}

data/apocalypse/lostcities/worldstyles/wasteland.json

{
  "outsidestyle": "outside",
  "citystyles": [
    { "factor": 1.0, "citystyle": "apocalypse:downtown" }
  ]
}

Two references, and both need the namespace. "wasteland" on the profile crashes the server on the first chunk. "downtown" inside the world style fails every chunk that tries to place a city. "outside" is correct bare, because lostcities:outside is a style the mod itself ships. game test

The profile's own file name never takes a namespace. apocalypse.json makes a profile called apocalypse, and config/lostcities/common.toml wires it to a dimension by that bare name. code review

Two real strategies¶

Use your own namespaceOverride the defaults

A file under your own namespace collides with nothing, and every reference to it, everywhere, needs the full name. game test

data/apocalypse/lostcities/worldstyles/wasteland_city.json

A file at the exact same path as a built-in one replaces the mod's shipped version of it entirely, so anything expecting the original lostcities:standard behaviour gets yours instead. game test

data/lostcities/lostcities/worldstyles/standard.json

Most modpacks are better off with their own namespace, and overriding is worth it only to replace a specific built-in deliberately.

How an override resolves¶

The pack latest in load order wins, and it wins the whole file. Two packs were given the same palette, one of them defining an extra character the other did not, and the extra character did not survive into the result. Swapping which pack held which file flipped the outcome exactly, so it is position that decides rather than content. game test

That is different from how two other things in this system behave, and the difference catches people: game test

	Merges	Replaces game test
Two datapacks, same asset name		yes, whole file game test
Block tags	yes
A city style's `inherit` chain	yes, within one file's chain
A part palette over a building palette	yes, per character	game test

So overriding citystyle_config to change one setting means restating everything else that file held, not only the key you came for. game test

Nothing tells you an override happened

The losing file is never seen and no message names it. In the test above, the only sign was one failed chunk reporting Could not find entry 'M' in the palette for part '<part>'!, which is the same message an ordinary undefined character produces. It names the character, not the collision that removed it. game test

/reload does not pick up Lost Cities asset changes

These registries are read once, when the world loads. In 7.4.12 the mod registers no reload listener, and vanilla does not reload datapack registries on /reload either. Editing a part or palette and running /reload changes nothing. code review

In single player, leaving the world and rejoining does clear the mod's asset cache, so the next chunks generated use your edits. On a dedicated server it takes a full server restart. See Seeing your changes. code review