I wasn't sure if there should be backwards compatibility left in for v0.9 or not. I'm not very solid with Lua, so I don't know if that if/else makes sense to 'solve' backwards compatibility.

Thank you, we do need to retain compatibility.

Those tests work - has 0.10 will still be true for 0.11...

This gives me an error that is_enabled is not defined.

Error executing vim.schedule lua callback: ...re/nvim/lazy/nvim-tree.lua/lua/nvim-tree/diagnostics.lua:44: attempt to call field 'is_enabled' (a nil value)
stack traceback:
	...re/nvim/lazy/nvim-tree.lua/lua/nvim-tree/diagnostics.lua:44: in function 'from_nvim_lsp'
	...re/nvim/lazy/nvim-tree.lua/lua/nvim-tree/diagnostics.lua:158: in function 'callback'
	...al/share/nvim/lazy/nvim-tree.lua/lua/nvim-tree/utils.lua:422: in function <...al/share/nvim/lazy/nvim-tree.lua/lua/nvim-tree/utils.lua:421>

❯ nvim --version
NVIM v0.10.0-dev-2499+g0d553c834
Build type: RelWithDebInfo
LuaJIT 2.1.1707061634

Let's revert this one. It looks like it's not present in older 0.10 builds, which people do actively use.

Reverted in #2784

We need some other implementation of that check then as it affects users on new enough versions.

We need some other implementation of that check then as it affects users on new enough versions.

Yes. Now that stable is 0.10 we should add 0.9 back to the matrix.

The 0.10 dev versions are a problem; API broke many times.

Edit: we might be able to test for pre-release: :h api-metadata

Fortunately, API levels have been implemented and are available since 0.9

#2787

We'll need to increase the minimum supported version to 0.9.

Unfortunately we're not going to get any value out of CI as 0.9 lacks the API symbols.