Add Mason and Null-ls plugins for Neovim

lua/custom/plugins/null-ls.lua

@@ -0,0 +1,36 @@
+return {
+  "jose-elias-alvarez/null-ls.nvim",
+  config = function()
+    local null_ls     = require("null-ls")
+
+    local formatting  = null_ls.builtins.formatting  -- to setup formatters
+    local diagnostics = null_ls.builtins.diagnostics -- to setup linters
+
+    local augroup     = vim.api.nvim_create_augroup("LspFormatting", {})
+
+    null_ls.setup({
+      sources = {
+        formatting.prettierd,
+        diagnostics.eslint_d
+      },
+      on_attach = function(current_client, bufnr)
+        if current_client.supports_method("textDocument/formatting") then
+          vim.api.nvim_clear_autocmds({ group = augroup, buffer = bufnr })
+          vim.api.nvim_create_autocmd("BufWritePre", {
+            group = augroup,
+            buffer = bufnr,
+            callback = function()
+              vim.lsp.buf.format({
+                filter = function(client)
+                  --  only use null-ls for formatting instead of lsp server
+                  return client.name == "null-ls"
+                end,
+                bufnr = bufnr,
+              })
+            end,
+          })
+        end
+      end
+    })
+  end
+}