Add alias as additionalTextEdits (#722)

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

@@ -7,7 +7,9 @@ defmodule ElixirLS.LanguageServer.Providers.Completion do
   with the Language Server Protocol. We also attempt to determine the context based on the line
   text before the cursor so we can filter out suggestions that are not relevant.
   """
+  alias ElixirLS.LanguageServer.Protocol.TextEdit
   alias ElixirLS.LanguageServer.SourceFile
+  import ElixirLS.LanguageServer.Protocol, only: [range: 4]
 
   @enforce_keys [:label, :kind, :insert_text, :priority, :tags]
   defstruct [
@@ -21,7 +23,8 @@ defmodule ElixirLS.LanguageServer.Providers.Completion do
     :priority,
     :tags,
     :command,
-    {:preselect, false}
+    {:preselect, false},
+    :additional_text_edit
   ]
 
   @func_snippets %{
@@ -102,8 +105,10 @@ defmodule ElixirLS.LanguageServer.Providers.Completion do
 
     # TODO: Don't call into here directly
     # Can we use ElixirSense.Providers.Suggestion? ElixirSense.suggestions/3
+    metadata = ElixirSense.Core.Parser.parse_string(text, true, true, line)
+
     env =
-      ElixirSense.Core.Parser.parse_string(text, true, true, line)
+      metadata
       |> ElixirSense.Core.Metadata.get_env(line)
 
     scope =
@@ -139,8 +144,18 @@ defmodule ElixirLS.LanguageServer.Providers.Completion do
       module: env.module
     }
 
+    position_to_insert_alias =
+      ElixirSense.Core.Metadata.get_position_to_insert_alias(metadata, line) || {line, 0}
+
+    context =
+      Map.put(
+        context,
+        :position_to_insert_alias,
+        SourceFile.elixir_position_to_lsp(text, position_to_insert_alias)
+      )
+
     items =
-      ElixirSense.suggestions(text, line, character)
+      ElixirSense.suggestions(text, line, character, required_alias: true)
       |> maybe_reject_derived_functions(context, options)
       |> Enum.map(&from_completion_item(&1, context, options))
       |> maybe_add_do(context)
@@ -285,6 +300,44 @@ defmodule ElixirLS.LanguageServer.Providers.Completion do
     }
   end
 
+  defp from_completion_item(
+         %{
+           type: :module,
+           name: name,
+           summary: summary,
+           subtype: subtype,
+           metadata: metadata,
+           required_alias: required_alias
+         },
+         %{
+           def_before: nil,
+           position_to_insert_alias: {line_to_insert_alias, column_to_insert_alias}
+         },
+         options
+       ) do
+    completion_without_additional_text_edit =
+      from_completion_item(
+        %{type: :module, name: name, summary: summary, subtype: subtype, metadata: metadata},
+        %{def_before: nil},
+        options
+      )
+
+    alias_value =
+      Atom.to_string(required_alias)
+      |> String.replace_prefix("Elixir.", "")
+
+    indentation = 1..column_to_insert_alias//1 |> Enum.map(fn _ -> " " end) |> Enum.join()
+    alias_edit = indentation <> "alias " <> alias_value <> "\n"
+
+    struct(completion_without_additional_text_edit,
+      additional_text_edit: %TextEdit{
+        range: range(line_to_insert_alias, 0, line_to_insert_alias, 0),
+        newText: alias_edit
+      },
+      documentation: alias_value <> "\n" <> summary
+    )
+  end
+
   defp from_completion_item(
          %{type: :module, name: name, summary: summary, subtype: subtype, metadata: metadata},
          %{def_before: nil},
@@ -989,6 +1042,12 @@ defmodule ElixirLS.LanguageServer.Providers.Completion do
       "filterText" => item.filter_text,
       "sortText" => String.pad_leading(to_string(idx), 8, "0"),
       "insertText" => item.insert_text,
+      "additionalTextEdits" =>
+        if item.additional_text_edit do
+          [item.additional_text_edit]
+        else
+          nil
+        end,
       "command" => item.command,
       "insertTextFormat" =>
         if Keyword.get(options, :snippets_supported, false) do

apps/language_server/test/providers/completion_test.exs

@@ -368,6 +368,48 @@ defmodule ElixirLS.LanguageServer.Providers.CompletionTest do
   end
 
   describe "structs and maps" do
+    test "suggests full module path as additionalTextEdits" do
+      text = """
+      defmodule MyModule do
+        @moduledoc \"\"\"
+        This
+        is a
+        long
+        moduledoc
+
+        \"\"\"
+
+        def dummy_function() do
+          ExampleS
+          #       ^
+        end
+      end
+      """
+
+      {line, char} = {10, 12}
+      TestUtils.assert_has_cursor_char(text, line, char)
+
+      {:ok, %{"items" => items}} = Completion.completion(text, line, char, @supports)
+
+      assert [item] = items
+
+      # 22 is struct
+      assert item["kind"] == 22
+      assert item["label"] == "ExampleStruct (struct)"
+
+      assert [%{newText: "alias ElixirLS.LanguageServer.Fixtures.ExampleStruct\n"}] =
+               item["additionalTextEdits"]
+
+      assert [
+               %{
+                 range: %{
+                   "end" => %{"character" => 0, "line" => 8},
+                   "start" => %{"character" => 0, "line" => 8}
+                 }
+               }
+             ] = item["additionalTextEdits"]
+    end
+
     test "completions of structs are rendered as a struct" do
       text = """
       defmodule MyModule do