Suggest an appropriate module name with the 'defmodule' snippet

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

@@ -565,7 +565,9 @@ defmodule ElixirLS.LanguageServer.Providers.Completion do
         completion
       end
 
-    if snippet = snippet_for({origin, name}, context) do
+    file_path = Keyword.get(options, :file_path)
+
+    if snippet = snippet_for({origin, name}, Map.put(context, :file_path, file_path)) do
       %{completion | insert_text: snippet, kind: :snippet, label: name}
     else
       completion
@@ -576,6 +578,12 @@ defmodule ElixirLS.LanguageServer.Providers.Completion do
     nil
   end
 
+  defp snippet_for({"Kernel", "defmodule"}, %{file_path: file_path}) when is_binary(file_path) do
+    # In a mix project the file_path can be something like "/some/code/path/project/lib/project/sub_path/my_file.ex"
+    # so we'll try to guess the appropriate module name from the path
+    "defmodule #{suggest_module_name(file_path)}$1 do\n\t$0\nend"
+  end
+
   defp snippet_for(key, %{pipe_before?: true}) do
     # Get pipe-friendly version of snippet if available, otherwise fallback to standard
     Map.get(@pipe_func_snippets, key) || Map.get(@func_snippets, key)
@@ -593,6 +601,75 @@ defmodule ElixirLS.LanguageServer.Providers.Completion do
     end
   end
 
+  def suggest_module_name(file_path) when is_binary(file_path) do
+    file_path
+    |> Path.split()
+    |> Enum.reverse()
+    |> do_suggest_module_name()
+  end
+
+  defp do_suggest_module_name([]), do: nil
+
+  defp do_suggest_module_name([filename | reversed_path]) do
+    filename
+    |> String.split(".")
+    |> case do
+      [file, "ex"] ->
+        do_suggest_module_name(reversed_path, [file], topmost_parent: "lib")
+
+      [file, "exs"] ->
+        if String.ends_with?(file, "_test") do
+          do_suggest_module_name(reversed_path, [file], topmost_parent: "test")
+        else
+          nil
+        end
+
+      _otherwise ->
+        nil
+    end
+  end
+
+  defp do_suggest_module_name([dir | _rest], module_name_acc, topmost_parent: topmost)
+       when dir == topmost do
+    module_name_acc
+    |> Enum.map(&Macro.camelize/1)
+    |> Enum.join(".")
+  end
+
+  defp do_suggest_module_name(
+         [probable_phoenix_dir | [project_web_dir | _] = rest],
+         module_name_acc,
+         opts
+       )
+       when probable_phoenix_dir in [
+              "controllers",
+              "views",
+              "channels",
+              "plugs",
+              "endpoints",
+              "sockets"
+            ] do
+    if String.ends_with?(project_web_dir, "_web") do
+      # by convention Phoenix doesn't use these folders as part of the module names
+      # for modules located inside them, so we'll try to do the same
+      do_suggest_module_name(rest, module_name_acc, opts)
+    else
+      # when not directly under the *_web folder however then we should make the folder
+      # part of the module's name
+      do_suggest_module_name(rest, [probable_phoenix_dir | module_name_acc], opts)
+    end
+  end
+
+  defp do_suggest_module_name([dir_name | rest], module_name_acc, opts) do
+    do_suggest_module_name(rest, [dir_name | module_name_acc], opts)
+  end
+
+  defp do_suggest_module_name([], _module_name_acc, _opts) do
+    # we went all the way up without ever encountering a 'lib' or a 'test' folder
+    # so we ignore the accumulated module name because it's probably wrong/useless
+    nil
+  end
+
   def function_snippet(name, args, arity, opts) do
     snippets_supported? = Keyword.get(opts, :snippets_supported, false)
     trigger_signature? = Keyword.get(opts, :trigger_signature?, false)

apps/language_server/lib/language_server/server.ex

@@ -685,7 +685,8 @@ defmodule ElixirLS.LanguageServer.Server do
         tags_supported: tags_supported,
         signature_help_supported: signature_help_supported,
         locals_without_parens: locals_without_parens,
-        signature_after_complete: signature_after_complete
+        signature_after_complete: signature_after_complete,
+        file_path: SourceFile.path_from_uri(uri)
       )
     end
 

apps/language_server/test/providers/completion_test.exs

@@ -908,6 +908,62 @@ defmodule ElixirLS.LanguageServer.Providers.CompletionTest do
                """
              }
     end
+
+    test "will suggest defmodule with module_name snippet when file path matches **/lib/**/*.ex" do
+      text = """
+      defmod
+      #     ^
+      """
+
+      {line, char} = {0, 6}
+
+      TestUtils.assert_has_cursor_char(text, line, char)
+
+      assert {:ok, %{"items" => [first | _] = _items}} =
+               Completion.completion(
+                 text,
+                 line,
+                 char,
+                 @supports
+                 |> Keyword.put(
+                   :file_path,
+                   "/some/path/my_project/lib/my_project/sub_folder/my_file.ex"
+                 )
+               )
+
+      assert %{
+               "label" => "defmodule",
+               "insertText" => "defmodule MyProject.SubFolder.MyFile$1 do\n\t$0\nend"
+             } = first
+    end
+
+    test "will suggest defmodule without module_name snippet when file path does not match expected patterns" do
+      text = """
+      defmod
+      #     ^
+      """
+
+      {line, char} = {0, 6}
+
+      TestUtils.assert_has_cursor_char(text, line, char)
+
+      assert {:ok, %{"items" => [first | _] = _items}} =
+               Completion.completion(
+                 text,
+                 line,
+                 char,
+                 @supports
+                 |> Keyword.put(
+                   :file_path,
+                   "/some/path/my_project/lib/my_project/sub_folder/my_file.heex"
+                 )
+               )
+
+      assert %{
+               "label" => "defmodule",
+               "insertText" => "defmodule $1 do\n\t$0\nend"
+             } = first
+    end
   end
 
   describe "generic suggestions" do
@@ -1053,4 +1109,79 @@ defmodule ElixirLS.LanguageServer.Providers.CompletionTest do
       assert insert_text =~ "if do\n\t"
     end
   end
+
+  describe "suggest_module_name/1" do
+    import Completion, only: [suggest_module_name: 1]
+
+    test "returns nil if current file_path is empty" do
+      assert nil == suggest_module_name("")
+    end
+
+    test "returns nil if current file is not an .ex file" do
+      assert nil == suggest_module_name("some/path/lib/dir/file.heex")
+    end
+
+    test "returns nil if current file is an .ex file but no lib folder exists in path" do
+      assert nil == suggest_module_name("some/path/not_lib/dir/file.ex")
+    end
+
+    test "returns nil if current file is an *_test.exs file but no test folder exists in path" do
+      assert nil == suggest_module_name("some/path/not_test/dir/file_test.exs")
+    end
+
+    test "returns an appropriate suggestion if file directly under lib" do
+      assert "MyProject" == suggest_module_name("some/path/my_project/lib/my_project.ex")
+    end
+
+    test "returns an appropriate suggestion if file arbitrarily nested under lib/" do
+      assert "MyProject.Foo.Bar.Baz.MyFile" =
+               suggest_module_name("some/path/my_project/lib/my_project/foo/bar/baz/my_file.ex")
+    end
+
+    test "returns an appropriate suggestion if file directly under test/" do
+      assert "MyProjectTest" ==
+               suggest_module_name("some/path/my_project/test/my_project_test.exs")
+    end
+
+    test "returns an appropriate suggestion if file arbitrarily nested under test" do
+      assert "MyProject.Foo.Bar.Baz.MyFileTest" ==
+               suggest_module_name(
+                 "some/path/my_project/test/my_project/foo/bar/baz/my_file_test.exs"
+               )
+    end
+
+    test "returns an appropriate suggestion if file is part of an umbrella project" do
+      assert "MySubApp.Foo.Bar.Baz" ==
+               suggest_module_name(
+                 "some/path/my_umbrella_project/apps/my_sub_app/lib/my_sub_app/foo/bar/baz.ex"
+               )
+    end
+
+    test "returns appropriate suggestions for modules nested under known phoenix dirs" do
+      [
+        {"MyProjectWeb.MyController", "controllers/my_controller.ex"},
+        {"MyProjectWeb.MyPlug", "plugs/my_plug.ex"},
+        {"MyProjectWeb.MyView", "views/my_view.ex"},
+        {"MyProjectWeb.MyChannel", "channels/my_channel.ex"},
+        {"MyProjectWeb.MyEndpoint", "endpoints/my_endpoint.ex"},
+        {"MyProjectWeb.MySocket", "sockets/my_socket.ex"}
+      ]
+      |> Enum.each(fn {expected_module_name, partial_path} ->
+        path = "some/path/my_project/lib/my_project_web/#{partial_path}"
+        assert expected_module_name == suggest_module_name(path)
+      end)
+    end
+
+    test "uses known Phoenix dirs as part of a module's name if these are not located directly beneath the *_web folder" do
+      assert "MyProject.Controllers.MyController" ==
+               suggest_module_name(
+                 "some/path/my_project/lib/my_project/controllers/my_controller.ex"
+               )
+
+      assert "MyProjectWeb.SomeNestedDir.Controllers.MyController" ==
+               suggest_module_name(
+                 "some/path/my_project/lib/my_project_web/some_nested_dir/controllers/my_controller.ex"
+               )
+    end
+  end
 end