Use LSP provider if available or tree-sitter as fallback

[gbrlsnchs]

Feature description

I've seen in the examples that you can either use LSP plus regular fallback or tree-sitter plus regular fallback, but can you use LSP when available, then tree-sitter as the fallback? Some filetypes don't have such LSP support but do have tree-sitter support.

Describe the solution you'd like

Use LSP provider if available, otherwise fall back to tree-sitter provider and only if none is available, then fall back to the default one.

Additional context

No response

[kevinhwang91]

TLDR;

nvim-ufo/doc/example.lua

Lines 23 to 52 in 480209a

	-- lsp->treesitter->indent
	local function selectProviderWithChainByDefault()
	local ftMap = {
	vim = 'indent',
	python = {'indent'},
	git = ''
	}
	local function customizeSelector(bufnr)
	local function handleFallbackException(err, providerName)
	if type(err) == 'string' and err:match('UfoFallbackException') then
	return require('ufo').getFolds(providerName, bufnr)
	else
	return require('promise').reject(err)
	end
	end
	return require('ufo').getFolds('lsp', bufnr):catch(function(err)
	return handleFallbackException(err, 'treesitter')
	end):catch(function(err)
	return handleFallbackException(err, 'indent')
	end)
	end
	require('ufo').setup({
	provider_selector = function(bufnr, filetype, buftype)
	return ftMap[filetype] or customizeSelector
	end
	})
	end

main provider may throw UfoFallbackException error to wake up fallback provider. If you want to use lsp->treesitter->indent chain, you must add the customized provider yourself. ufo has given an example.

Never consider adding this example to README because I haven't seen a fallback chain for a client to request servers that I think it is fragile.

edit: example is changed