🔧 Fix julials setup in single file mode

This workaround is required due to the issue described in:

williamboman/mason-lspconfig.nvim#423

lua/plugins/lsp.lua

@@ -12,6 +12,8 @@ local servers = {
   -- Julia Language Server -----------------------------------------------------------------
 
   julials = {
+    julia_env_path = "~/.julia/environments/v1.10/",
+
     settings = {
       julia = {
         inlayHints = {
@@ -24,7 +26,66 @@ local servers = {
           }
         }
       }
-    }
+    },
+
+    on_new_config = function(config, workspace_dir)
+      local _    = require("mason-core.functional")
+      local fs   = require("mason-core.fs")
+      local path = require("mason-core.path")
+
+      -- The default configuration used by `mason-lspconfig`:
+      --
+      --   https://github.com/williamboman/mason-lspconfig.nvim/blob/main/lua/mason-lspconfig/server_configurations/julials/init.lua
+      --
+      -- has the following logic to obtain the current environment path:
+      --
+      --   1. Check if `env_path` is defined.
+      --   2. Check if we are in a Julia project.
+      --   3. Call julia to return the current env path.
+      --
+      -- However, the third step causes a significant slow down when Julia is called in a
+      -- single file mode because it must wait loading Julia. Here, we will invert the
+      -- logic:
+      --
+      --   1. Check if we are in a Julia project.
+      --   2. Check if `env_path` is defined.
+      --   3. Call julia to return the current env path.
+      --
+      -- Hence, if we define `env_path`, we can still use the project folder as root and
+      -- avoid the slowdown in the single file case.
+      local env_path = nil
+      local file_exists = _.compose(fs.sync.file_exists, path.concat, _.concat { workspace_dir })
+      if (file_exists { "Project.toml" } and file_exists { "Manifest.toml" }) or
+        (file_exists { "JuliaProject.toml" } and file_exists { "JuliaManifest.toml" }) then
+        env_path = workspace_dir
+      end
+
+      if not env_path then
+        env_path = config.julia_env_path and vim.fn.expand(config.julia_env_path)
+      end
+
+      if not env_path then
+        local ok, env = pcall(vim.fn.system, {
+          "julia",
+          "--startup-file=no",
+          "--history-file=no",
+          "-e",
+          "using Pkg; print(dirname(Pkg.Types.Context().env.project_file))",
+        })
+        if ok then
+          env_path = env
+        end
+      end
+
+      config.cmd = {
+        vim.fn.exepath "julia-lsp",
+        env_path,
+      }
+      config.cmd_env = vim.tbl_extend("keep", config.cmd_env or {}, {
+        SYMBOL_SERVER = config.symbol_server,
+        SYMBOL_CACHE_DOWNLOAD = (config.symbol_cache_download == false) and "0" or "1",
+      })
+    end,
   },
 
   -- Lua Language Server -------------------------------------------------------------------
@@ -171,7 +232,7 @@ return {
 
     config = function()
       require("mason").setup()
-      require('mason-lspconfig').setup()
+      require("mason-lspconfig").setup()
       require("mason-lspconfig").setup_handlers({
         function (server_name)
           local server = servers[server_name] or {}