perf: cache diagnostics, fire mode events less often (#115)

* ref: separate updating the diagnostics and applying virtual text

When checking some lags I had, `tiny-inline-diagnostic` seemed to be the
main culprit, and more precisely the number of call to
`vim.diagnostic.get`. This introduces a cache for the diagnostics to
avoid that call, separating updating the data and displaying it.

* feat: prevents triggering USER_EVENT on every mode change

The mode can change *a lot* in a short period of time (several times in
a second when doing a surround with mini.ai for instance). The issue is
that we were calling `enable` each time the mode changed, which
triggered the `USER_EVENT` events and in particular the
`apply_virtual_texts` function. This led to a lot of unnecessary
computation and redraw of the diagnostics, in turn making Neovim laggy,
especially in the presence of many diagnostics.

We instead only fire the event if we were disabled. If the text or the
position of the cursor has changed, the other events
(`DiagnosticChanged`, `CursorMoved`, ..) should take care of updating
the diagnostics and the virtual text.

* fix: prevent diag source to be appended multiple times to message

* fix: don't overwrite the diagnostics from other sources

When using multiple sources, the diagnostics coming from
`DiagnosticChanged` can be multiple and disjoint if coming from
different sources. We thus need to overwrite only the diagnostics of the
incoming source.

* ref: filter diags at write time rather than read time

The assumption is that writing happens less often than reading and
because of that we chose to keep a single array to read with all the
diagnostics instead of one array per buffer and per source and having to
create a new concatenated table each time we read them.

To get the best of both world we could:
- Have some kind of nested iterators that goes through each source and
  array. This would be problematic though if we need to sort the data
  between the two sources.
- Have a separate cache for the concatenated version of the diagnostics
  that's populated at read time and then re-used and cleared at write
  time.

* fix: diagnostics not cleared when they should

When we get an empty array in the `DiagnosticChanged` events, it means
that one of the namespace has been cleared. The problem is that we don't
(and can't) know which one it was without calling `vim.diagnostic.get`
to get all the diagnostics.

Author: Kazy

lua/tiny-inline-diagnostic/chunk.lua

@@ -263,11 +263,12 @@ function M.get_chunks(opts, diags_on_line, diag_index, diag_line, cursor_line, b
 		show_source = true
 	end
 
+	local diag_message = diag.message
 	if show_source and diag.source then
-		diag.message = diag.message .. " (" .. diag.source .. ")"
+		diag_message = diag_message .. " (" .. diag.source .. ")"
 	end
 
-	local chunks = { diag.message }
+	local chunks = { diag_message }
 	local severities = vim.tbl_map(function(d)
 		return d.severity
 	end, diags_on_line)
@@ -280,7 +281,6 @@ function M.get_chunks(opts, diags_on_line, diag_index, diag_line, cursor_line, b
 		end
 	end
 
-	local diag_message = diag.message
 
 	if opts.options.format and diag_message then
 		diag_message = opts.options.format(diag)

lua/tiny-inline-diagnostic/diagnostic.lua

@@ -15,18 +15,27 @@ M.enabled = true
 M.user_toggle_state = true
 local attached_buffers = {}
 
+---Buffer number => diagnostics
+---@type table<number, any>
+local diagnostics_cache = {}
+
 ---@class DiagnosticPosition
 ---@field line number
 ---@field col number
 
 local function enable()
-	M.enabled = true
-	vim.api.nvim_exec_autocmds("User", { pattern = USER_EVENT })
+	-- Prevents calling `enable` even if it's not needed
+	if not M.enabled then
+		M.enabled = true
+		vim.api.nvim_exec_autocmds("User", { pattern = USER_EVENT })
+	end
 end
 
 local function disable()
-	M.enabled = false
-	vim.api.nvim_exec_autocmds("User", { pattern = USER_EVENT })
+	if M.enabled then
+		M.enabled = false
+		vim.api.nvim_exec_autocmds("User", { pattern = USER_EVENT })
+	end
 end
 
 -- Diagnostic filtering functions
@@ -87,22 +96,16 @@ end
 ---@param diagnostics table
 ---@return table
 local function filter_diagnostics(opts, event, diagnostics)
-	local filtered = filter_by_severity(opts, diagnostics)
-
-	table.sort(filtered, function(a, b)
-		return a.severity < b.severity
-	end)
-
 	if not opts.options.multilines.enabled then
-		return M.filter_diags_under_cursor(opts, event.buf, filtered)
+		return M.filter_diags_under_cursor(opts, event.buf, diagnostics)
 	end
 
 	if opts.options.multilines.always_show then
-		return filtered
+		return diagnostics
 	end
 
-	local under_cursor = M.filter_diags_under_cursor(opts, event.buf, filtered)
-	return not vim.tbl_isempty(under_cursor) and under_cursor or filtered
+	local under_cursor = M.filter_diags_under_cursor(opts, event.buf, diagnostics)
+	return not vim.tbl_isempty(under_cursor) and under_cursor or diagnostics
 end
 
 ---@param diagnostics table
@@ -122,6 +125,53 @@ local function get_visible_diagnostics(diagnostics)
 	return visible_diags
 end
 
+---@param opts DiagnosticConfig
+---@param bufnr number
+---@param diagnostics table
+local function update_diagnostics_cache(opts, bufnr, diagnostics)
+	if vim.tbl_isempty(diagnostics) then
+		-- The event doesn't contain the associated namespace of the diagnostics, 
+		-- meaning we can't know which namespace was cleared. We thus have to get 
+		-- the diagnostics through normal means.
+		local diags = vim.diagnostic.get(bufnr)
+		table.sort(diags, function(a, b)
+			return a.severity < b.severity
+		end)
+		diagnostics_cache[bufnr] = diags
+		return
+	end
+
+	local diag_buf = diagnostics_cache[bufnr] or {}
+
+	-- Do the upfront work of filtering and sorting
+	diagnostics = filter_by_severity(opts, diagnostics)
+
+	-- Find the sources of the incoming diagnostics.
+	-- It's almost always a single source, but you never know.
+	local sources = {}
+	for _, diag in ipairs(diagnostics) do
+		if not vim.tbl_contains(sources, diag.source) then
+			table.insert(sources, diag.source)
+		end
+	end
+
+	-- Clear the diagnostics that are from the incoming source
+	diag_buf = vim.tbl_filter(function(diag)
+		return not vim.tbl_contains(sources, diag.source)
+	end, diag_buf)
+
+	-- Insert and sort the results
+	for _, diag in pairs(diagnostics) do
+		table.insert(diag_buf, diag)
+	end
+
+	table.sort(diag_buf, function(a, b)
+		return a.severity < b.severity
+	end)
+
+	diagnostics_cache[bufnr] = diag_buf
+end
+
 ---@param opts DiagnosticConfig
 ---@param event table
 local function apply_virtual_texts(opts, event)
@@ -139,9 +189,9 @@ local function apply_virtual_texts(opts, event)
 		return
 	end
 
-	-- Get and validate diagnostics
-	local ok, diagnostics = pcall(vim.diagnostic.get, event.buf)
-	if not ok or vim.tbl_isempty(diagnostics) then
+	-- Get diagnostics and clear them if needed
+	local diagnostics = diagnostics_cache[event.buf] or {}
+	if vim.tbl_isempty(diagnostics) then
 		extmarks.clear(event.buf)
 		return
 	end
@@ -214,6 +264,7 @@ end
 local function detach_buffer(buf)
 	timers.close(buf)
 	attached_buffers[buf] = nil
+	diagnostics_cache[buf] = nil
 end
 
 ---@param autocmd_ns number
@@ -274,8 +325,9 @@ local function setup_buffer_autocmds(autocmd_ns, opts, event, throttled_apply)
 	-- Setup diagnostic change events
 	vim.api.nvim_create_autocmd("DiagnosticChanged", {
 		group = autocmd_ns,
-		callback = function()
-			if vim.api.nvim_buf_is_valid(event.buf) then
+		callback = function(args)
+			if vim.api.nvim_buf_is_valid(args.buf) then
+				update_diagnostics_cache(opts, args.buf, args.data.diagnostics)
 				vim.api.nvim_exec_autocmds("User", { pattern = USER_EVENT })
 			end
 		end,