mix help app:APP: Always try loading apps and support Erlang apps (#14894)

Author: wojtekmach

lib/mix/lib/mix/tasks/help.ex

@@ -114,10 +114,19 @@ defmodule Mix.Tasks.Help do
     loadpaths!()
     app = String.to_atom(app)
 
+    # If the application is not available, attempt to load it from Erlang/Elixir
+    if is_nil(Application.spec(app, :vsn)) do
+      try do
+        Mix.ensure_application!(app)
+      rescue
+        _ -> :ok
+      end
+    end
+
     if modules = Application.spec(app, :modules) do
       for module <- modules,
           not (module |> Atom.to_string() |> String.starts_with?("Elixir.Mix.Tasks.")),
-          {:docs_v1, _, :elixir, "text/markdown", %{"en" => <<doc::binary>>}, _, _} <-
+          {:docs_v1, _, _, "text/markdown", %{"en" => <<doc::binary>>}, _, _} <-
             [Code.fetch_docs(module)] do
         leading = doc |> String.split(["\n\n", "\r\n\r\n"], parts: 2) |> hd()
         "# #{inspect(module)}\n#{leading}\n"

lib/mix/test/mix/tasks/help_test.exs

@@ -199,14 +199,23 @@ defmodule Mix.Tasks.HelpTest do
     in_tmp(context.test, fn ->
       output =
         capture_io(fn ->
-          Mix.Tasks.Help.run(["app:mix"])
+          Mix.Tasks.Help.run(["app:iex"])
         end)
 
-      assert output =~ "# Mix\n\nMix is a build tool"
+      assert output =~ "# IEx\n\nElixir's interactive shell."
+
+      if System.otp_release() >= "27" do
+        output =
+          capture_io(fn ->
+            Mix.Tasks.Help.run(["app:parsetools"])
+          end)
+
+        assert output =~ "# :leex"
+      end
     end)
   end
 
-  test "help unknown app:APP", context do
+  test "help app:UNKNOWN", context do
     in_tmp(context.test, fn ->
       Mix.Tasks.Help.run(["app:foobar"])
       assert_received {:mix_shell, :error, ["Application foobar does not exist or is not loaded"]}