Add compilers option to Mix.install/2

lib/mix/lib/mix.ex

@@ -884,6 +884,7 @@ defmodule Mix do
         config: [],
         config_path: nil,
         consolidate_protocols: true,
+        compilers: nil,
         elixir: nil,
         force: false,
         lockfile: nil,
@@ -899,6 +900,12 @@ defmodule Mix do
     consolidate_protocols? = Keyword.fetch!(opts, :consolidate_protocols)
     start_applications? = Keyword.fetch!(opts, :start_applications)
 
+    compilers =
+      case Keyword.fetch!(opts, :compilers) do
+        nil -> [:elixir]
+        [_ | _] = compilers -> compilers
+      end
+
     id =
       {deps, config, system_env, consolidate_protocols?}
       |> :erlang.term_to_binary()
@@ -923,7 +930,8 @@ defmodule Mix do
         dynamic_config = [
           deps: deps,
           consolidate_protocols: consolidate_protocols?,
-          config_path: config_path
+          config_path: config_path,
+          compilers: compilers
         ]
 
         :ok =
@@ -1093,7 +1101,6 @@ defmodule Mix do
       app: @mix_install_app,
       erlc_paths: [],
       elixirc_paths: [],
-      compilers: [:elixir],
       prune_code_paths: false
     ] ++ dynamic_config
   end

lib/mix/test/mix_test.exs

@@ -43,7 +43,7 @@ defmodule MixTest do
       assert Protocol.consolidated?(InstallTest.Protocol)
 
       assert_received {:mix_shell, :info, ["==> install_test"]}
-      assert_received {:mix_shell, :info, ["Compiling 2 files (.ex)"]}
+      assert_received {:mix_shell, :info, ["Compiling 3 files (.ex)"]}
       assert_received {:mix_shell, :info, ["Generated install_test app"]}
       refute_received _
 
@@ -71,7 +71,7 @@ defmodule MixTest do
 
       assert File.dir?(Path.join(tmp_dir, "installs"))
       assert_received {:mix_shell, :info, ["==> install_test"]}
-      assert_received {:mix_shell, :info, ["Compiling 2 files (.ex)"]}
+      assert_received {:mix_shell, :info, ["Compiling 3 files (.ex)"]}
       assert_received {:mix_shell, :info, ["Generated install_test app"]}
       refute_received _
 
@@ -361,7 +361,7 @@ defmodule MixTest do
         ])
 
         assert_received {:mix_shell, :info, ["==> install_test"]}
-        assert_received {:mix_shell, :info, ["Compiling 2 files (.ex)"]}
+        assert_received {:mix_shell, :info, ["Compiling 3 files (.ex)"]}
         assert_received {:mix_shell, :info, ["Generated install_test app"]}
         refute_received _
 
@@ -430,6 +430,29 @@ defmodule MixTest do
       System.delete_env("MIX_INSTALL_RESTORE_PROJECT_DIR")
     end
 
+    test "custom compilers", %{tmp_dir: tmp_dir} do
+      Mix.install(
+        [
+          {:install_test, path: Path.join(tmp_dir, "install_test")}
+        ],
+        compilers: [:elixir, :install_test]
+      )
+
+      assert File.dir?(Path.join(tmp_dir, "installs"))
+
+      assert Protocol.consolidated?(InstallTest.Protocol)
+
+      assert_received {:mix_shell, :info, ["==> install_test"]}
+      assert_received {:mix_shell, :info, ["Compiling 3 files (.ex)"]}
+      assert_received {:mix_shell, :info, ["Generated install_test app"]}
+      assert_received {:mix_shell, :info, ["==> mix_install"]}
+      assert_received {:mix_shell, :info, ["Hello from custom compiler!"]}
+      refute_received _
+
+      assert List.keyfind(Application.started_applications(), :install_test, 0)
+      assert apply(InstallTest, :hello, []) == :world
+    end
+
     test "installed?", %{tmp_dir: tmp_dir} do
       refute Mix.installed?()
 
@@ -509,6 +532,20 @@ defmodule MixTest do
       end
       """)
 
+      File.mkdir_p!("#{tmp_dir}/install_test/lib/mix/tasks/compile/")
+
+      File.write!("#{tmp_dir}/install_test/lib/mix/tasks/compile/install_test.ex", """
+      defmodule Mix.Tasks.Compile.InstallTest do
+        use Mix.Task.Compiler
+
+        def run(_args) do
+          Mix.shell().info("Hello from custom compiler!")
+
+          :noop
+        end
+      end
+      """)
+
       [tmp_dir: tmp_dir]
     end