PSA: Don't do what I did (keeping a backup XML file inside the package folder structure)

[MSFS 2024] Questions & Community Discussions SDK: Tools/Samples/Documentation
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I actually came on here to ask a question, but I figured out what went wrong and wanted to post it here as a cautionary tale.

Note: I’m not an experienced FS developer. I’m an experienced developer in other software realms, but not MSFS. So, if what I did is obviously stupid to other people, this post is not for you. This is for other people like me who don’t know everything.

What I did wrong:

Before making a major change to my airport project, I made a backup of my package XML file and kept the backup file inside the same Windows folder as the main XML file that the SDK uses, like this mockup, below (where “ABCD” is the airport code):

File and backup in the same place

I then made the change in the SDK, saved my work, and exited MSFS 2024.

The error it caused:

The next time I opened my package in the Project Inspector, the Scenery Editor (which would normally contain dozens of objects from my previous work) was blank, and I was being prompted with a modal dialog, entitled Asset path selection:

Asset path selection

I don’t know what this dialog wanted me to do (there’s no Submit button or any choices to make), but clearly, something was corrupted.

Root cause analysis:

The root cause was that there were two XML files in the same place, and it would seem that the SDK was only looking for one and didn’t know which one to choose. As soon as I removed the backup XML file from the folder structure and tried to reopen the package, the package loaded fine.

If I go into the PackageDefinitions folder of my project and examine the XML there, I’ll find that inside my “scenery” <AssetGroup/>, there’s a child node, <AssetDir/> containing the path to the XML file of my package. Note that it’s specifying a directory and not a specific filename:

<AssetGroup Name="scenery">
	<Type Version="0">Airport</Type>
	<Flags>
		<FSXCompatibility>false</FSXCompatibility>
	</Flags>
	<AssetDir>PackageSources\Scenery\airport-abcd-blahblahblah\scenery\</AssetDir>
	<OutputDir>Scenery\airport-abcd-blahblahblah\scenery\</OutputDir>
</AssetGroup>

My guess is that I could probably rename that one XML file to anything at all, and so long as it has the .xml extension, the Scenery Editor wouldn’t care and it would open up just fine. I tried renaming the file to something else, and voila, it opened. I’m not going to try and extensively test this functionality, but it seems to me it’s opening up *.xml, and so long as it finds one and only one file, it’s fine.

This happened in MSFS 2024. I’m not going to try all this in the 2020 SDK, but I’ll bet that I’d experience the same issue there, too.

Open questions I still have:

  1. I’m wondering why the XML structure specifies an AssetDir, as opposed to an AssetFile or something like that. Is there a use case where the SDK is going to be looking for more than one file?
  2. What was that Asset path selection modal dialog looking for? With nothing to select, it did not look like I could fix the problem (e.g., choosing an XML file to open) within the SDK.
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