Group modules by app for umbrella projects by default

Author: robertoaloi

Diff for: README.md

@@ -120,6 +120,8 @@ It is also possible to specify multiple `ebin` directories in the case of _umbre
    $ ex_doc "PROJECT_NAME" "PROJECT_VERSION" _build/dev/lib/app1/ebin _build/dev/lib/app2/ebin -m "PROJECT_MODULE" -u "https://github.com/GITHUB_USER/GITHUB_REPO" -l path/to/logo.png
    ```
 
+If multiple `ebin` directories are specified, modules are grouped by application by default. It is possible to override this behaviour by providing a custom `groups_per_modules` option.
+
 You can specify a config file via the `--config` option, both Elixir and Erlang formats are supported. Invoke `ex_doc` without arguments to learn more.
 
 <!-- tabs-close -->

Diff for: lib/ex_doc/config.ex

@@ -115,7 +115,10 @@ defmodule ExDoc.Config do
 
     {groups_for_docs, options} = Keyword.pop(options, :groups_for_docs, [])
     {groups_for_extras, options} = Keyword.pop(options, :groups_for_extras, [])
-    {groups_for_modules, options} = Keyword.pop(options, :groups_for_modules, [])
+    apps = Keyword.get(options, :apps, [])
+
+    {groups_for_modules, options} =
+      Keyword.pop(options, :groups_for_modules, default_groups_for_modules(apps))
 
     {skip_undefined_reference_warnings_on, options} =
       Keyword.pop(
@@ -278,4 +281,15 @@ defmodule ExDoc.Config do
   defp append_slash(url) do
     if :binary.last(url) == ?/, do: url, else: url <> "/"
   end
+
+  defp default_groups_for_modules([_app]) do
+    []
+  end
+
+  defp default_groups_for_modules(apps) do
+    Enum.map(apps, fn app ->
+      Application.load(app)
+      {app, Application.spec(app, :modules)}
+    end)
+  end
 end

Diff for: test/ex_doc/cli_test.exs

@@ -3,6 +3,7 @@ defmodule ExDoc.CLITest do
   import ExUnit.CaptureIO
 
   @ebin "_build/test/lib/ex_doc/ebin"
+  @ebin2 "_build/test/lib/makeup/ebin"
 
   defp run(args) do
     with_io(fn -> ExDoc.CLI.main(args, &{&1, &2, &3}) end)
@@ -64,6 +65,14 @@ defmodule ExDoc.CLITest do
     assert catch_exit(run(["ExDoc"])) == {:shutdown, 1}
   end
 
+  test "multiple apps" do
+    {[{"ExDoc", "1.2.3", html}, {"ExDoc", "1.2.3", epub}], _io} =
+      run(["ExDoc", "1.2.3", @ebin, @ebin2])
+
+    assert [:ex_doc, :makeup] = Enum.sort(Keyword.get(html, :apps))
+    assert [:ex_doc, :makeup] = Enum.sort(Keyword.get(epub, :apps))
+  end
+
   test "arguments that are not aliased" do
     File.write!("not_aliased.exs", ~s([key: "val"]))