Ensure Mix.install/2 can be called after errors with deps (#11011)

Author: wojtekmach

lib/mix/lib/mix.ex

@@ -576,17 +576,19 @@ defmodule Mix do
 
     :ok = Mix.Local.append_archives()
     :ok = Mix.ProjectStack.push(__MODULE__.InstallProject, config, "nofile")
+    build_dir = Path.join(dir, "_build")
 
     try do
-      run_deps? = not File.dir?(Path.join(dir, "_build"))
+      run_deps? = not File.dir?(build_dir)
       File.mkdir_p!(dir)
 
       File.cd!(dir, fn ->
         if run_deps? do
           Mix.Task.rerun("deps.get")
         end
 
-        Mix.Task.run("compile")
+        Mix.Task.rerun("deps.loadpaths")
+        Mix.Task.rerun("compile")
       end)
 
       for app <- Mix.Project.deps_apps() do

lib/mix/test/mix_test.exs

@@ -85,6 +85,20 @@ defmodule MixTest do
       end
     end
 
+    test "install after errors", %{tmp_dir: tmp_dir} do
+      assert_raise Mix.Error, "Can't continue due to errors on dependencies", fn ->
+        Mix.install([
+          {:bad, path: Path.join(tmp_dir, "bad")}
+        ])
+      end
+
+      Mix.install([
+        {:install_test, path: Path.join(tmp_dir, "install_test")}
+      ])
+
+      assert apply(InstallTest, :hello, []) == :world
+    end
+
     test "consolidate_protocols: false", %{tmp_dir: tmp_dir} do
       Mix.install(
         [