WIP: added true, false and nil as keywords for completion (#978)

Co-authored-by: KevinKalb <kevin.kalb@aponia.de>

Author: Kevin Kalb

apps/language_server/lib/language_server/providers/completion.ex

@@ -161,6 +161,7 @@ defmodule ElixirLS.LanguageServer.Providers.Completion do
       |> Enum.map(&from_completion_item(&1, context, options))
       |> maybe_add_do(context)
       |> maybe_add_end(context)
+      |> maybe_add_keywords(context)
       |> Enum.reject(&is_nil/1)
       |> sort_items()
 
@@ -238,8 +239,40 @@ defmodule ElixirLS.LanguageServer.Providers.Completion do
     end
   end
 
+  defp maybe_add_keywords(completion_items, %{text_after_cursor: ""} = context) do
+    kw = Map.get(context, :text_before_cursor) |> String.trim_leading() |> get_keyword()
+
+    if kw != "" do
+      item = %__MODULE__{
+        label: kw,
+        kind: :keyword,
+        detail: "keyword",
+        insert_text: kw,
+        tags: [],
+        priority: 0
+      }
+
+      [item | completion_items]
+    else
+      completion_items
+    end
+  end
+
+  defp maybe_add_keywords(completion_items, _context) do
+    completion_items
+  end
+
   ## Helpers
 
+  defp get_keyword(t) do
+    cond do
+      Enum.member?(["t", "tr", "tru", "true"], t) -> "true"
+      Enum.member?(["f", "fa", "fal", "fals", "false"], t) -> "false"
+      Enum.member?(["n", "ni", "nil"], t) -> "nil"
+      true -> ""
+    end
+  end
+
   defp is_incomplete(items) do
     if Enum.empty?(items) do
       false

apps/language_server/test/providers/completion_test.exs

@@ -685,6 +685,42 @@ defmodule ElixirLS.LanguageServer.Providers.CompletionTest do
     end
   end
 
+  describe "keyword completion" do
+    setup do
+      text = """
+      defmodule MyModule do
+        def dummy_function() do
+          t
+          #^
+        end
+      end
+      """
+
+      %{text: text, location: {2, 5}}
+    end
+
+    test "first", context do
+      %{text: text, location: {line, char}} = context
+
+      TestUtils.assert_has_cursor_char(text, line, char)
+
+      opts = Keyword.merge(@supports, signature_after_complete: true)
+      {:ok, %{"items" => items}} = Completion.completion(text, line, char, opts)
+
+      [item] = items |> Enum.filter(&(&1["insertText"] == "true"))
+
+      assert %{
+               "detail" => "keyword",
+               "documentation" => %{:kind => "markdown", "value" => ""},
+               "insertText" => "true",
+               "insertTextFormat" => 2,
+               "kind" => 14,
+               "label" => "true",
+               "sortText" => "00000000"
+             } = item
+    end
+  end
+
   describe "function completion" do
     setup do
       text = """