add scala and sbt support (#986)

lua/lang/scala.lua

@@ -0,0 +1,80 @@
+local M = {}
+
+M.config = function()
+  O.lang.scala = {
+    metals = {
+      active = false,
+      server_version = "0.10.5",
+      excluded_packages = {},
+      show_implicit_arguments = false,
+      show_inferred_type = true,
+      status_bar_provider = false,
+    },
+    formatter = {
+      exe = "scalafmt",
+      args = { "--stdin" },
+      stdin = true,
+    },
+  }
+end
+
+M.format = function()
+  O.formatters.filetype["scala"] = {
+    function()
+      return {
+        exe = O.lang.scala.formatter.exe,
+        args = O.lang.scala.formatter.args,
+        stdin = O.lang.scala.formatter.stdin,
+      }
+    end,
+  }
+  O.formatters.filetype["sbt"] = O.formatters.filetype["scala"]
+  --  To understand sbt files on stdin, scalafmt needs to assume any old filename
+  --  that ends in .sbt.  Using a dummy filename instead of the actual one is
+  --  required to support buffers of sbt filetype without the extension.
+  O.formatters.filetype["sbt"].args = { "--stdin", "--assume-filename", "foo.sbt" }
+
+  require("formatter.config").set_defaults {
+    logging = false,
+    filetype = O.formatters.filetype,
+  }
+end
+
+M.lint = function()
+  -- TODO: implement linters (if applicable)
+  return "No linters configured!"
+end
+
+M.lsp = function()
+  -- enable metal server integration
+  if O.lang.scala.metals.active then
+    vim.g["metals_server_version"] = O.lang.scala.metals.server_version
+    -- https://github.com/scalameta/nvim-metals#prerequisites
+    vim.opt_global.shortmess:remove("F"):append "c"
+    local metals_config = require("metals").bare_config
+    metals_config.on_attach = function()
+      require("completion").on_attach()
+    end
+    metals_config.handlers["textDocument/publishDiagnostics"] =
+      vim.lsp.with(vim.lsp.diagnostic.on_publish_diagnostics, {
+        virtual_text = {
+          prefix = "",
+        },
+      })
+    metals_config.settings = {
+      showImplicitArguments = O.lang.scala.metals.show_implicit_arguments,
+      showInferredType = O.lang.scala.metals.show_inferred_type,
+      excludedPackages = O.lang.scala.metals.excluded_packages,
+    }
+    metals_config.init_options.statusBarProvider = O.lang.scala.metals.status_bar_provider
+    require "lsp"
+    require("metals").initialize_or_attach(metals_config)
+  end
+end
+
+M.dap = function()
+  -- TODO: implement dap
+  return "No DAP configured!"
+end
+
+return M