nvim: Improve marksman zk link handling

Instead of completely detaching marksman as soon as we are in a
zettelkasten directory, this disables displaying the 'non-existent link'
diagnostic instead. Only disables signs and virtual_text for now (still
displayed as diagnostic in e.g. Trouble windows) but should provide a
good first step into more fine-grained control.
Oh if only marksman just provided a flag to toggle this feature..

nvim/.config/nvim/lua/plugins/lsp.lua

@@ -239,9 +239,40 @@ return {
 				on_attach = function(client, bufnr)
 					-- TODO: for some reason this stays true even after rootdir switch?
 					if client.config.in_zk_notebook then
-						vim.defer_fn(function()
+						local default_handler = vim.diagnostic.handlers.virtual_text
-							vim.lsp.buf_detach_client(bufnr, client.id)
+						vim.diagnostic.handlers.virtual_text = {
-						end, 1000)
+							show = function(namespace, bufnrr, diagnostics, opts)
+								for i, diagnostic in ipairs(diagnostics) do
+									if
+										diagnostic.source
+										== "Marksman" -- You need to check what the correct value should be here
+									then
+										table.remove(diagnostics, i)
+									end
+								end
+								default_handler.show(namespace, bufnrr, diagnostics, opts)
+							end,
+							hide = function(...)
+								default_handler.hide(...)
+							end,
+						}
+						local default_handler = vim.diagnostic.handlers.signs
+						vim.diagnostic.handlers.signs = {
+							show = function(namespace, bufnrr, diagnostics, opts)
+								for i, diagnostic in ipairs(diagnostics) do
+									if
+										diagnostic.source
+										== "Marksman" -- You need to check what the correct value should be here
+									then
+										table.remove(diagnostics, i)
+									end
+								end
+								default_handler.show(namespace, bufnrr, diagnostics, opts)
+							end,
+							hide = function(...)
+								default_handler.hide(...)
+							end,
+						}
 					end
 					on_attach(client, bufnr)
 				end,