Ensure path dependencies manifests point to the proper path

Closes #1888

Author: José Valim

lib/mix/lib/mix/deps.ex

@@ -180,13 +180,18 @@ defmodule Mix.Deps do
   """
   def in_dependency(dep, post_config // [], fun)
 
-  def in_dependency(Mix.Dep[app: app, opts: opts], post_config, fun) do
+  def in_dependency(Mix.Dep[app: app, opts: opts], config, fun) do
+    # Set the app_path to be the one stored in the dependency.
+    # This is important because the name of application in the
+    # mix.exs file can be different than the actual name and we
+    # choose to respect the one in the mix.exs.
+    config  = Keyword.put(config, :app_path, opts[:build])
     env     = opts[:env] || :prod
     old_env = Mix.env
 
     try do
       Mix.env(env)
-      Mix.Project.in_project(app, opts[:dest], post_config, fun)
+      Mix.Project.in_project(app, opts[:dest], config, fun)
     after
       Mix.env(old_env)
     end

lib/mix/lib/mix/tasks/deps.compile.ex

@@ -84,13 +84,7 @@ defmodule Mix.Tasks.Deps.Compile do
     :ok
   end
 
-  defp do_mix(Mix.Dep[app: app, opts: opts] = dep, config) do
-    # Set the app_path to be the one stored in the dependency.
-    # This is important because the name of application in the
-    # mix.exs file can be different than the actual name and we
-    # choose to respect the one in the mix.exs.
-    config = Keyword.put(config, :app_path, opts[:build])
-
+  defp do_mix(Mix.Dep[app: app] = dep, config) do
     Mix.Deps.in_dependency dep, config, fn _ ->
       case dev_compilation(app, config) do
         { source, target } ->
@@ -122,7 +116,7 @@ defmodule Mix.Tasks.Deps.Compile do
   defp dev_compilation(app, config) do
     if config[:build_per_environment] do
       source = config[:build_path] |> Path.dirname |> Path.join("dev/lib/#{app}")
-      target = Mix.Project.manifest_path(config)
+      target = Mix.Project.manifest_path
       source != target && Mix.Deps.Lock.mix_env(source) == to_string(Mix.env) &&
         not Mix.Utils.stale?([target], [source]) && { source, target }
     else

lib/mix/test/mix/umbrella_test.exs

@@ -177,7 +177,7 @@ defmodule Mix.UmbrellaTest do
 
         future = { { 2020, 4, 17 }, { 14, 0, 0 } }
 
-        manifest = "../foo/_build/shared/lib/foo/.compile.elixir"
+        manifest = "_build/shared/lib/foo/.compile.elixir"
         File.mkdir_p!(Path.dirname(manifest))
         File.touch!(manifest, future)
         assert Mix.Tasks.Compile.Elixir.run([]) == :ok