Since I use this myself and it was requested often, I forked the mod and fixed all known (to me) off-by-one bugs.

See https://mods.factorio.com/mod/LandfillEverythingContinued/

Hello!

First of all, I am really sorry that the mod hasn't been updated. I sort of drifted away for a while, a bit burned out I guess, but that isn't an excuse, just an explanation. I updated the game yesterday and I'm about to be more active again. I also sort of believed not many people used it!

You absolutely have my permission to fork it and continue, but as I get a 404 when I click the link I am also more than happy to incorporate your changes and release a new version instead if you prefer. I just started to try to get the mod to run again...

Somehow and extra slash crept in at the end, the working link would be https://mods.factorio.com/mod/LandfillEverythingContinued

I mostly changed rotate and the way landfill boxes are calculated, all of which, I think, are actually bugfixes. If you'd incoporate those, I'd be externally grateful and could discontinue the fork :)

Welcome back commander! Your mod has a lot of downloads, i think its much appreciated. Once i got used to it i really missed the mod after 1.0. Luckily someone posted update instructions in one of the threads. I followed them (about the same time schmorp did:p) which led to another fork:
https://mods.factorio.com/mod/LandfillEverythingU.

I added space exploration tiles to the define.lua (and incorporated schmorps changes up until 1.1.8.) I also unsuccesfully have been looking into GUI, as a exercise. I am willing to continue supporting the mod, however as i feel the least experienced of us, i'd be fine with depricating my fork as well (considering what would be best for the community).

One of my personal wishes for the future is excluding offshore-pump, to prevent land-filling your water inlets.

I just sort of got to a state where my bad conscience for not keeping up with changes and updating just gave me anxiety, but I am hopefully over it!

The way offshore-pumps are supposed to work is to add a tile so it can be built, but not over the inlet so it can still suck water. This is crucial for stamping down nuclear on a lake, my main use case, so I don't think excluding them completely will work.

Regarding the GUI there probably should be a shortcut button or perhaps refactor it into a upgrade planner. The button was suitable for 0.17! Biggest issue right now is that you can't landfill blueprints from the library any more. That requires probably creating a new temp blueprint and replace the one you have in the hand.

I am also planning to put the project on github which will make it easier to submit patches etc but need to clean up a few things first. I am not an experienced Factorio modder by any means, but I desperately wanted the functionality!

Personally im fine with the top button, as i have more buttons there from other mods to form a proper toolbar. (I just started experimenting because there was a user suggestion which was worked out very nice in "Quickbar templates").
You are correct about the pumps, however currently they also get filled on the water side.
In my opinion the library thing is mainly a vanilla thing, requiring you to duplicate bp's to your inventory anyhow, if you don't want lose them on the go (but that may be my own "wrong" workflow). I could perhaps see benefit of applying landfill directly to your library prints. Git is a good idea as next step. Take the time you need, the mod is already, in current state, very valuable!

Regarding opff-shore pumps, in my fork they are filled "correctly" (the game has a bigger bounding box, so it fills more than necessary, but it does leave out the water inlet tiles).

I think it would be cool if waterfill would be added below the adjacent tile bounding box :)

Nice to see this mod updated! I was actually in process of creating yet another fork :) Good I checked beforehand. What I wanted to ask is whether you managed to fix issue with it not working anymore with BPs from library? When I last checked sources, such BP is not a real item stack anymore, and player.cursor_stack.valid_for_read returns false, making BP inaccessible. Existing APIs https://lua-api.factorio.com/latest/LuaControl.html#LuaControl.is_cursor_blueprint and https://lua-api.factorio.com/latest/LuaControl.html#LuaControl.get_blueprint_entities don't seem to be enough.

Indeed, in this mod the offshore pumps are not filled correctly. When I have time next I will investigate what the difference is between mine and the original (if there is any, and this isn't just a fluke).

I also sort of believed not many people used it!

Sorry for the noise, but I wanted to let you know that this mod is part of my "essentials", a group of mods without which I would enjoy the game a lot less. As a fellow modder, I understand that perhaps we do not see enough appreciation, since the people that tend to reach out are more likely those with an issue rather than those who are just happy. So here goes. Thank you for this mod!