I have additional information that hopefully will help find a solution.

- First, this bug is still present in Factorio 2.1.9.

- Second, I have come up with a very minimal reproduction. All steps require the `control.lua` I posted earlier to be enabled in a mod, which is basically just calling `set ...

The following two methods:

https://lua-api.factorio.com/latest/classes/LuaItemCommon.html#get_blueprint_entity_tags
https://lua-api.factorio.com/latest/classes/LuaRecord.html#get_blueprint_entity_tags

are documented as returning non-optional `Tags`. However, they can both return `nil` if the ...

Okay, I think I understand better what is going on here. I made an interface improvement request instead: viewtopic.php?t=134458

Currently, if a blueprint containing a `SimpleEntityWithOwner` is pasted over an existing `SimpleEntityWithOwner` in the world, if the `direction`s would end up being different, Factorio declines to build/red-outlines the entity.

I propose an entity-prototype-flag or boolean be added, applicable at ...

I second the general request for a "SimpleEntityWithOwner + mirroring" entity type that represent a minimal moddable entity that has the full gamut of orientation support.

Current Behavior
When a blueprinted simple-entity-with-owner stacks on top of a corresponding simple-entity-with-owner in the world, if their `direction`s aren't the same, the blueprint can't be built in the ordinary mode.

It CAN be built in forced mode (not superforce, ordinary shift force) but ...

`get_undo_item_count()` and `get_redo_item_count()` (fortunately) still exist in the game but appear to have incorrectly been removed from the docs for 2.1.7

I do believe there is a perhaps greater bug here than the original report would indicate.

Linked input control is a red herring. The bug is that `custom-input` events linked to `mouse-button-1` (and possibly other mouse buttons or bindings though I have not explicitly tested those), exhibit ...

Several of us from the Discord are attempting to mod in the ability to virtually-rotate and flip kitbashed compound entites that cannot normally be rotated and flipped according to the base engine.

It turns out that through a series of black magicks we have largely been able to implement this ...

I agree that this behavior is bad and should be addressed in some way. Personally I think it should just allow invalid objects to pass with the understanding that mods receiving mod-generated custom events must validate payloads.

That being said, there is a workaround possible in current API: I ...

I believe I may have further isolated the cause from further testing:

- If the "Snap to Grid" options for the BP being replaced are disabled altogether, the issue does not occur.

- When "Snap to Grid" is enabled, the various grid-snapping values contribute to the issue, with different values ...

The Issue
When "Select New Contents For This Blueprint" is used, during the corresponding `on_player_setup_blueprint` event, calling `.set_blueprint_entities()` with the (unmodified) return result from `.get_blueprint_entities()`, corrupts the blueprint. Specifically it appears to shift rail ...

Those do seem to be conflicting... but the question is what's the more useful behavior? I can easily remove the nil entries from the push if that's what seems most useful.


I have run into this as well.

- I would also like to know under what particular circumstances or reasons the entries ...

`on_undo_applied` does not fire until after the operation is complete. I need an event that fires before. Event tracing reveals no such ordinary game event.

The custom input event does in fact fire at the needed time, but only if CTRL+Z is pressed. If the undo GUI button is pressed, it does not ...

Reproduction steps:

1) Add the following prototype in data phase:

data:extend({
{
type = "custom-input",
name = "things-linked-undo",
key_sequence = "",
linked_game_control = "undo",
},
})


2) In control phase, monitor when the above custom input fires, e.g.

script.on_event("things ...

(Spawned from a discord discussion beginning here: https://discord.com/channels/139677590393716737/306402592265732098/1418345907954515989 )

In order of difficulty level:

1) By analogy with https://lua-api.factorio.com/latest/classes/LuaEntity.html#supports_direction I would like to request that ...

(In the #mod-dev-help discord channel, Bilka asked for a forum post to be made about this issue. Link to the original discord discussion: here )

We received the following multiplayer crash report:

09-11-2025, 14-34-14.png



Upon analysis, we found the crash is occurring in the `on_pre_build ...

Seconded. This could save considerably Lua time in any mod that uses combinators for gathering input.

For Project Cybersyn we have considered various workarounds, up to and including just forcing the priorities of all same-named stops to 50. Ultimately we settled on issueing a warning when a controlled train lands at a stop with priority not equal to 50.

We have simply been telling people not to ...

With the addition of the new and very helpful LuaSchedule API, I thought it would be a good time to raise this issue again. Having to use intermediating rail stops causes fundamental issues with the builtin priority and train limits systems.

Being able to schedule a train directly to a specific ...