How is "Open with" on macOS populated internally?

I know I can associate my application with a certain extension by editing the Info.plist file in my app bundle:

...
<key>CFBundleTypeExtensions</key>
  <array>
    <string>myext</string>
</array>

While this works, my "Open with" list gets littered with duplicate entries of the different versions of the application I'm developing on that machine. There are even entries for really old versions that I've never opened on that very computer! (It's a new machine being synced with Dropbox so there are older releases in my file system.)

It seems as macOS would scan for app bundles even outside of /Application and adds all applications it finds to "Open with". A workaround is to reset the "Open with" list with this command I found somewhere here on SO I think: /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain user;killall Finder

How is the "Open with" list populated internally? Is macOS really scanning my drive looking for Info.plist files with CFBundleTypeExtensions entries? And is there any way to avoid having my "Open with" list littered with older versions other then deleting (or zipping) them?

NB: I'm not using Xcode but build my application on the command line using the clang compilers and creating Info.plist by a bash script.

Solution

How is the "Open with" list populated internally? Is macOS really scanning my drive looking for Info.plist files with CFBundleTypeExtensions entries?

I think so, yes. Check the documentation for Launch Services, specifically the section "Application Registration". Specifically, the OS can find your app and register is in the following ways:

A built-in background tool, run whenever the system is booted or a new user logs in, automatically searches the Applications folders in the system, network, local, and user domains and registers any new applications it finds there. (This operation is analogous to “rebuilding the desktop” in earlier versions of Mac OS.)

The Finder automatically registers all applications as it becomes aware of them, such as when they are dragged onto the user’s disk or when the user navigates to a folder containing them.

When the user attempts to open a document for which no preferred application can be found in the Launch Services database, the Finder presents a dialog asking the user to select an application with which to open the document. It then registers that application before launching it.

And is there any way to avoid having my "Open with" list littered with older versions other then deleting (or zipping) them?

I'm not sure about that part. Probably not, although it seems like once you reset the Launch Services database using the command in your question, the old versions shouldn't get added back to the Open With list unless you are doing something to trigger getting re-added. Is that the case?