Share _build path when running commands from umbrella

Author: José Valim

lib/mix/lib/mix/task.ex

@@ -211,8 +211,9 @@ defmodule Mix.Task do
     recursive = recursive(module)
 
     if umbrella? && recursive && Mix.ProjectStack.enable_recursion do
+      config = [build_path: Mix.Project.build_path]
       res = lc Mix.Dep[app: app, opts: opts] inlist Mix.Deps.Umbrella.loaded do
-        Mix.Project.in_project(app, opts[:path], fun)
+        Mix.Project.in_project(app, opts[:path], config, fun)
       end
       Mix.ProjectStack.disable_recursion
       res

lib/mix/test/mix/umbrella_test.exs

@@ -146,7 +146,10 @@ defmodule Mix.UmbrellaTest do
         purge [Bar]
 
         future = { { 2020, 4, 17 }, { 14, 0, 0 } }
-        File.touch!("_build/lib/foo/.compile.elixir", future)
+
+        manifest = "../foo/_build/lib/foo/.compile.elixir"
+        File.mkdir_p!(Path.dirname(manifest))
+        File.touch!(manifest, future)
         assert Mix.Tasks.Compile.Elixir.run([]) == :ok
       end)
     end)