feat(rust): add bacon-ls and improve debugging (LazyVim#3212)

**NOTE: the PR will be in draft until
mason-org/mason-registry#5774 is not merged**

Some improvements in the Rust extra

- Set `codelldb` adapter for rustacean.nvim
- Add support for [bacon-ls](https://github.com/crisidev/bacon-ls)
([blog post](https://lmno.lol/crisidev/bacon-language-server))

`bacon-ls` can be used as an alternative to `rust-analyzer` for
diagnostics, improving `rust-analyzer` performances. This is configured
by `vim.g.lazyvim_rust_diagnostics`, which can be set to `rust-analyzer`
or `bacon-lsp`.

<img width="1063" alt="screenshot"
src="https://github.com/LazyVim/LazyVim/assets/1781140/f50a38ff-0ec0-4d10-8cdc-796d027b16f0">

---------

Co-authored-by: Iordanis Petkakis <12776461+dpetka2001@users.noreply.github.com>

lua/lazyvim/plugins/extras/lang/rust.lua

@@ -1,5 +1,12 @@
-local map = LazyVim.keymap_set
-local k = require("lazyvim.keymaps").get_keymaps()
+if lazyvim_docs then
+  -- LSP Server to use for Rust.
+  -- Set to "bacon-ls" to use bacon-ls instead of rust-analyzer.
+  -- only for diagnostics. The rest of LSP support will still be
+  -- provided by rust-analyzer.
+  vim.g.lazyvim_rust_diagnostics = "rust-analyzer"
+end
+
+local diagnostics = vim.g.lazyvim_rust_diagnostics or "rust-analyzer"
 
 return {
   recommended = function()
@@ -38,7 +45,13 @@ return {
   {
     "williamboman/mason.nvim",
     optional = true,
-    opts = { ensure_installed = { "codelldb" } },
+    opts = function(_, opts)
+      opts.ensure_installed = opts.ensure_installed or {}
+      vim.list_extend(opts.ensure_installed, { "codelldb" })
+      if diagnostics == "bacon-ls" then
+        vim.list_extend(opts.ensure_installed, { "bacon" })
+      end
+    end,
   },
 
   {
@@ -65,8 +78,12 @@ return {
                 enable = true,
               },
             },
-            -- Add clippy lints for Rust.
-            checkOnSave = true,
+            -- Add clippy lints for Rust if using rust-analyzer
+            checkOnSave = diagnostics == "rust-analyzer",
+            -- Enable diagnostics if using rust-analyzer
+            diagnostics = {
+              enable = diagnostics == "rust-analyzer",
+            },
             procMacro = {
               enable = true,
               ignored = {
@@ -80,6 +97,16 @@ return {
       },
     },
     config = function(_, opts)
+      local package_path = require("mason-registry").get_package("codelldb"):get_install_path()
+      local codelldb = package_path .. "/extension/adapter/codelldb"
+      local library_path = package_path .. "/extension/lldb/lib/liblldb.dylib"
+      local uname = io.popen("uname"):read("*l")
+      if uname == "Linux" then
+        library_path = package_path .. "/extension/lldb/lib/liblldb.so"
+      end
+      opts.dap = {
+        adapter = require("rustaceanvim.config").get_codelldb_adapter(codelldb, library_path),
+      }
       vim.g.rustaceanvim = vim.tbl_deep_extend("keep", vim.g.rustaceanvim or {}, opts or {})
       if vim.fn.executable("rust-analyzer") == 0 then
         LazyVim.error(
@@ -95,6 +122,9 @@ return {
     "neovim/nvim-lspconfig",
     opts = {
       servers = {
+        bacon_ls = {
+          enabled = diagnostics == "bacon-ls",
+        },
         rust_analyzer = { enabled = false },
       },
     },