Revert "Include optional dependencies in extra_applications (#8263)"

Unfortunately adding optional dependencies doesn't work for umbrella
apps where each app has a different optional dependency. For example,
Ecto 3.0 has both jason and poison as optional deps. Imagine the two
umbrella children below:

    foo
      * ecto
      * jason

    bar
      * ecto
      * poison
      * jason

Because ecto is shared with both, Ecto will include both poison and
jason, which makes`foo` fail to boot when running in isolation.

Closes #7930.

Author: José Valim

lib/mix/lib/mix/dep.ex

@@ -132,13 +132,18 @@ defmodule Mix.Dep do
       for dep <- deps,
           dep.app == app,
           child <- dep.deps,
-          do: {child.app, true},
+          do: {child.app, Keyword.get(child.opts, :optional, false)},
           into: %{}
 
-    Enum.map(children, fn %{app: app} = dep ->
+    Enum.map(children, fn %{app: app, opts: opts} = dep ->
+      # optional only matters at the top level. Any non-top level dependency
+      # that is optional and is still available means it has been fulfilled.
       case top_level do
-        %{^app => _} -> %{dep | top_level: true}
-        %{} -> %{dep | top_level: false}
+        %{^app => optional} ->
+          %{dep | top_level: true, opts: Keyword.put(opts, :optional, optional)}
+
+        %{} ->
+          %{dep | top_level: false, opts: Keyword.delete(opts, :optional)}
       end
     end)
   end

lib/mix/lib/mix/tasks/compile.app.ex

@@ -212,7 +212,7 @@ defmodule Mix.Tasks.Compile.App do
     apps =
       properties
       |> Keyword.get(:applications)
-      |> Kernel.||(apps_from_prod_deps(properties, config))
+      |> Kernel.||(apps_from_prod_non_optional_deps(properties, config))
       |> normalize_apps(extra, config)
 
     Keyword.put(properties, :applications, apps)
@@ -317,11 +317,12 @@ defmodule Mix.Tasks.Compile.App do
     end)
   end
 
-  defp apps_from_prod_deps(properties, config) do
+  defp apps_from_prod_non_optional_deps(properties, config) do
     included_applications = Keyword.get(properties, :included_applications, [])
     non_runtime_deps = non_runtime_deps(config)
 
-    for %{app: app, top_level: true} <- Mix.Dep.cached(),
+    for %{app: app, opts: opts, top_level: true} <- Mix.Dep.cached(),
+        not Keyword.get(opts, :optional, false),
         not Map.has_key?(non_runtime_deps, app),
         app not in included_applications,
         do: app

lib/mix/test/mix/dep_test.exs

@@ -196,6 +196,31 @@ defmodule Mix.DepTest do
     end)
   end
 
+  test "nested deps with optional matching" do
+    Process.put(:custom_deps_git_repo_opts, optional: true)
+
+    # deps_repo brings git_repo but it is optional
+    deps = [
+      {:deps_repo, "0.1.0", path: "custom/deps_repo"},
+      {:git_repo, "0.1.0", git: MixTest.Case.fixture_path("git_repo")}
+    ]
+
+    with_deps(deps, fn ->
+      in_fixture("deps_status", fn ->
+        File.mkdir_p!("custom/deps_repo/lib")
+
+        File.write!("custom/deps_repo/lib/a.ex", """
+        # Check that the child dependency is top_level and optional
+        [%Mix.Dep{app: :git_repo, top_level: true, opts: opts}] = Mix.Dep.cached()
+        true = Keyword.fetch!(opts, :optional)
+        """)
+
+        Mix.Tasks.Deps.Get.run([])
+        Mix.Tasks.Deps.Compile.run([])
+      end)
+    end)
+  end
+
   test "nested deps with convergence and optional dependencies" do
     deps = [
       {:deps_repo, "0.1.0", path: "custom/deps_repo"},

lib/mix/test/mix/tasks/compile.app_test.exs

@@ -99,7 +99,7 @@ defmodule Mix.Tasks.Compile.AppTest do
       properties = parse_resource_file(:custom_deps)
 
       assert properties[:applications] ==
-               [:kernel, :stdlib, :elixir, :logger, :ok1, :ok3, :ok4, :ok6, :ok7]
+               [:kernel, :stdlib, :elixir, :logger, :ok1, :ok3, :ok4, :ok7]
     end)
   end