Print a nice prelude if we fail to load a project, closes #2430

Author: José Valim

lib/mix/lib/mix.ex

@@ -228,30 +228,17 @@ defmodule Mix do
   Raises a mix error that is nicely formatted.
   """
   def raise(message) when is_binary(message) do
-    Kernel.raise Mix.Error, mix: mix_info, message: message
+    Kernel.raise Mix.Error, mix: true, message: message
   end
 
   @doc """
   Raises a mix compatible exception.
 
-  A mix compatible exception has a `mix_error` field which mix
+  A mix compatible exception has a `mix` field which mix
   uses to store the project or application name which is
   automatically by the formatting tools.
   """
   def raise(exception, opts) when is_atom(exception) do
-    Kernel.raise %{exception.exception(opts) | mix: mix_info}
-  end
-
-  defp mix_info do
-    case Mix.ProjectStack.peek do
-      %{name: name, config: config, pos: pos} when pos > 0 ->
-        if app = config[:app] do
-          {:app, app}
-        else
-          {:project, name}
-        end
-      _ ->
-        :none
-    end
+    Kernel.raise %{exception.exception(opts) | mix: true}
   end
 end

lib/mix/lib/mix/cli.ex

@@ -75,21 +75,16 @@ defmodule Mix.CLI do
       exception ->
         stacktrace = System.stacktrace
 
-        if info = Map.get(exception, :mix) do
+        if Map.get(exception, :mix) do
           mod = exception.__struct__ |> Module.split() |> Enum.at(0, "Mix")
-          Mix.shell.error "** (#{mod})#{show_mix_info(info)} #{Exception.message(exception)}"
+          Mix.shell.error "** (#{mod}) #{Exception.message(exception)}"
+          exit({:shutdown, 1})
         else
           reraise exception, stacktrace
         end
-
-        exit({:shutdown, 1})
     end
   end
 
-  defp show_mix_info({:project, proj}), do: " [#{inspect proj}]"
-  defp show_mix_info({:app, app}),      do: " [#{app}]"
-  defp show_mix_info(:none),            do: ""
-
   defp change_env(task) do
     if nil?(System.get_env("MIX_ENV")) &&
        (env = preferred_cli_env(task)) do

lib/mix/lib/mix/project.ex

@@ -172,13 +172,19 @@ defmodule Mix.Project do
   def in_project(app, path, post_config \\ [], fun)
 
   def in_project(app, ".", post_config, fun) do
-    cached = load_project(app, post_config)
-    result = try do
+    cached = try do
+      load_project(app, post_config)
+    rescue
+      any ->
+        Mix.shell.error "Error while loading project #{inspect app} at #{File.cwd!}"
+        reraise any, System.stacktrace
+    end
+
+    try do
       fun.(cached)
     after
       Mix.Project.pop
     end
-    result
   end
 
   def in_project(app, path, post_config, fun) do
@@ -264,7 +270,7 @@ defmodule Mix.Project do
       app = config[:app] ->
         Path.join([build_path(config), "lib", Atom.to_string(app)])
       config[:apps_path] ->
-        raise "Trying to access app_path for an umbrella project but umbrellas have no app"
+        Mix.raise "Trying to access app_path for an umbrella project but umbrellas have no app"
       true ->
         Mix.raise "Cannot access build without an application name, " <>
           "please ensure you are in a directory with a mix.exs file and it defines " <>

lib/mix/test/mix/project_test.exs

@@ -88,6 +88,22 @@ defmodule Mix.ProjectTest do
     end
   end
 
+  test "in_project prints nice error message if fails to load file" do
+    in_fixture "no_mixfile", fn ->
+      File.write "mix.exs", """
+      raise "oops"
+      """
+
+      assert_raise RuntimeError, "oops", fn ->
+        Mix.Project.in_project :hello, ".", [], fn _ ->
+          :ok
+        end
+      end
+
+      assert_receive {:mix_shell, :error, ["Error while loading project :hello at" <> _]}
+    end
+  end
+
   test "config_files" do
     Mix.Project.push(SampleProject)
 
@@ -104,7 +120,7 @@ defmodule Mix.ProjectTest do
       refute "config/.exs" in files
     end
   end
-  
+
   defp assert_proj_dir_linked_or_copied(source, target, symlink_path) do
     case :file.read_link(source) do
       {:ok, path} -> assert path == symlink_path