feat(dart): Add support for dart closing labels (#6)

* Add support for dart closing labels

* Remove up-value for opts and wrap draw_labels in a closure getter

* Add example autocommand that draws the closing labels

* Adding back the defaults if they weren't passed in

* Refactor callback to make it a lot simpler

* Update README to include closing labels docs

Author: PatOConnor43

README.md

@@ -7,7 +7,7 @@ Repo to hold a bunch of info & extension callbacks for built-in LSP. Use at
 Requires Built-in LSP, [Neovim Nightly](https://github.com/neovim/neovim/releases/tag/nightly), [nvim-lsp](https://github.com/neovim/nvim-lsp)
 
 ```vimscript
-" LSP Extensions (inlay-hints)
+" LSP Extensions
 Plug 'tjdevries/lsp_extensions.nvim'
 ```
 
@@ -56,12 +56,20 @@ require'lsp_extensions'.inlay_hints{
 autocmd InsertLeave,BufEnter,BufWinEnter,TabEnter,BufWritePost *.rs :lua require'lsp_extensions'.inlay_hints{ prefix = ' » ', highlight = "NonText" }
 ```
 
+## Closing Labels (dartls)
+![closing-labels](https://raw.githubusercontent.com/tjdevries/media.repo/b4a4a20d0c31a4905e42e219cf854c9aa104edbd/lsp_extensions/dart-closingLabels.png)
+
+[Closing Labels Documentation](https://github.com/dart-lang/sdk/blob/master/pkg/analysis_server/tool/lsp_spec/README.md#darttextdocumentpublishclosinglabels-notification)
+
+Check out the [example file](examples/dart/closing_labels.lua) for setup
+
 ## Clips
 
 - Showing Line Diagnostics: https://clips.twitch.tv/ProductiveBoxyPastaCoolStoryBro
 
 - This Plugin:
 
   - Lined up hints: https://clips.twitch.tv/DaintyCorrectMarjoramKeepo
+  - [Closing Labels Demo](https://github.com/tjdevries/media.repo/blob/b4a4a20d0c31a4905e42e219cf854c9aa104edbd/lsp_extensions/dart-closingLabels.mp4)
 
 - N E O V I M: https://clips.twitch.tv/SmoothGoodTurnipCmonBruh

examples/dart/closing_labels.lua

@@ -0,0 +1,12 @@
+local nvim_lsp = require('nvim_lsp')
+
+nvim_lsp.dartls.setup{
+  init_options = {
+    closingLabels = true,
+  },
+  callbacks = {
+    -- get_callback can be called with or without arguments
+    ['dart/textDocument/publishClosingLabels'] = require('lsp_extensions.dart.closing_labels').get_callback({highlight = "Special", prefix = " >> "}),
+  },
+}
+

lua/lsp_extensions/dart/closing_labels.lua

@@ -0,0 +1,56 @@
+--[[
+## Closing Labels
+
+** Method: 'dart/textDocument/publishClosingLabels**
+Direction: Server -> Client Params: { uri: string, labels: { label: string, range: Range }[] }
+This notifies the client when closing label information is available (or updated) for a file.
+
+Since this is a notification, the callback needs to be registered in the client's callbacks table.
+This can be achieved with nvim_lspconfig with this minimal config.
+```lua
+nvim_lsp.dartls.setup{
+  init_options = {
+    closingLabels = true,
+  },
+  callbacks = {
+    ['dart/textDocument/publishClosingLabels'] = require('lsp_extensions.dart.closing_labels').get_callback{},
+  },
+}
+```
+https://github.com/dart-lang/sdk/blob/master/pkg/analysis_server/tool/lsp_spec/README.md#darttextdocumentpublishclosinglabels-notification
+--]]
+local M = {}
+
+-- Namespace for the virtual text
+local closing_labels_ns = vim.api.nvim_create_namespace('lsp_extensions.dart.closing_labels')
+
+-- Draws the newly published labels in the current buffer
+-- @tparam table a table of options: highlight, prefix
+-- @tparam table a table of labels for the current buffer
+local draw_labels = function(opts, labels)
+  opts = opts or {}
+  local highlight = opts.highlight or "Comment"
+  local prefix = opts.prefix or "// "
+  vim.api.nvim_buf_clear_namespace(0, closing_labels_ns, 0, -1)
+  for _, label in pairs(labels) do
+    local end_line = label.range["end"].line
+    local text = prefix .. label.label
+    vim.api.nvim_buf_set_virtual_text(0, closing_labels_ns, end_line, { { text, highlight } }, {})
+  end
+end
+
+-- Gets a callback to register to the dartls publishClosingLabels notification.
+-- @tparam table a table of options: highlight, prefix
+M.get_callback = function(opts)
+  return function(_, _, result, _, _)
+    local uri = result.uri
+    local labels = result.labels
+    -- This check is meant to prevent stray events from over-writing labels that
+    -- don't match the current buffer.
+    if uri == vim.uri_from_bufnr(0) then
+      draw_labels(opts, labels)
+    end
+  end
+end
+
+return M