Do not allow duplicated projects to be pushed onto the stack

Closes #1846

Author: José Valim

lib/mix/lib/mix/cli.ex

@@ -78,7 +78,8 @@ defmodule Mix.CLI do
   defp change_env(task) do
     if nil?(System.get_env("MIX_ENV")) && (env = Mix.project[:preferred_cli_env][task]) do
       Mix.env(env)
-      Mix.Project.push Mix.Project.pop
+      { project, file } = Mix.Project.pop
+      Mix.Project.push project, file
     end
   end
 

lib/mix/lib/mix/deps.ex

@@ -175,24 +175,10 @@ defmodule Mix.Deps do
   changing the current working directory and loading the given
   project onto the project stack.
 
-  In case the project is a rebar dependency, a `Mix.Rebar` project
-  will be pushed into the stack to simulate the rebar configuration.
-
   It is expected a fetched dependency as argument.
   """
   def in_dependency(dep, post_config // [], fun)
 
-  def in_dependency(Mix.Dep[manager: :rebar, opts: opts], post_config, fun) do
-    # Use post_config for rebar deps
-    Mix.Project.post_config(post_config)
-    Mix.Project.push(Mix.Rebar)
-    try do
-      File.cd!(opts[:dest], fn -> fun.(Mix.Rebar) end)
-    after
-      Mix.Project.pop
-    end
-  end
-
   def in_dependency(Mix.Dep[app: app, opts: opts], post_config, fun) do
     env     = opts[:env] || :prod
     old_env = Mix.env

lib/mix/lib/mix/deps/retriever.ex

@@ -144,8 +144,8 @@ defmodule Mix.Deps.Retriever do
     end)
   end
 
-  defp rebar_dep(Mix.Dep[] = dep, config) do
-    Mix.Deps.in_dependency(dep, config, fn _ ->
+  defp rebar_dep(Mix.Dep[opts: opts] = dep, config) do
+    File.cd!(opts[:dest], fn ->
       config = Mix.Rebar.load_config(".")
       extra  = Dict.take(config, [:sub_dirs])
       dep.manager(:rebar).extra(extra).deps(rebar_children(config))

lib/mix/lib/mix/project.ex

@@ -41,16 +41,21 @@ defmodule Mix.Project do
   # Invoked after each Mix.Project is compiled.
   @doc false
   def __after_compile__(env, _binary) do
-    push env.module
+    push env.module, env.file
   end
 
   # Push a project onto the project stack. Only
   # the top of the stack can be accessed.
   @doc false
-  def push(atom) when is_atom(atom) do
+  def push(atom, file // "nofile") when is_atom(atom) do
     config = Keyword.merge default_config, get_project_config(atom)
-
-    Mix.Server.cast({ :push_project, atom, config })
+    case Mix.Server.call({ :push_project, atom, config, file }) do
+      :ok ->
+        :ok
+      { :error, other } when is_binary(other) ->
+        raise Mix.Error, message: "Trying to load #{inspect atom} from #{inspect file}" <>
+          " but another project with the same was already defined at #{inspect other}"
+    end
   end
 
   # Pops a project from the stack.

lib/mix/lib/mix/rebar.ex

@@ -1,10 +1,6 @@
 defmodule Mix.Rebar do
   @moduledoc false
 
-  # Make Mix.Rebar work like a project so we can push it into the stack.
-  @doc false
-  def project, do: []
-
   @doc """
   Returns the path supposed to host the local copy of rebar.
   """

lib/mix/lib/mix/server.ex

@@ -5,7 +5,7 @@ defmodule Mix.Server do
   defrecord Config, tasks: :ordsets.new, projects: [], mixfile: [],
     shell: Mix.Shell.IO, scm: :ordsets.new, env: nil, post_config: []
 
-  defrecord Project, name: nil, config: nil, rec_enabled?: true, io_done: false
+  defrecord Project, name: nil, config: nil, rec_enabled?: true, io_done: false, file: nil
 
   def start_link(env) do
     :gen_server.start_link({ :local, __MODULE__ }, __MODULE__, env, [])
@@ -55,8 +55,8 @@ defmodule Mix.Server do
 
   def handle_call(:pop_project, _from, config) do
     case config.projects do
-      [ Project[name: project] | tail ] ->
-        { :reply, project, config.projects(tail) }
+      [ Project[name: name, file: file] | tail ] ->
+        { :reply, { name, file }, config.projects(tail) }
       _ ->
         { :reply, nil, config }
     end
@@ -87,10 +87,29 @@ defmodule Mix.Server do
     end
   end
 
+  def handle_call({ :push_project, name, config, file }, _from, state) do
+    config  = Keyword.merge(config, state.post_config)
+    project = Project[name: name, config: config, file: file]
+
+    cond do
+      file = has_project_named(name, state) ->
+        { :reply, { :error, file }, state }
+      true ->
+        { :reply, :ok, state.post_config([]).update_projects(&[project|&1]) }
+    end
+  end
+
   def handle_call(request, from, config) do
     super(request, from, config)
   end
 
+  defp has_project_named(name, state) do
+    name && Enum.find_value(state.projects, fn
+      Project[name: ^name, file: file] -> file
+      Project[] -> nil
+    end)
+  end
+
   def handle_cast({ :shell, name }, config) do
     { :noreply, config.shell(name) }
   end
@@ -111,14 +130,6 @@ defmodule Mix.Server do
     { :noreply, config.update_tasks &:ordsets.filter(fn {t, _} -> t != task end, &1) }
   end
 
-  def handle_cast({ :push_project, name, conf }, config) do
-    conf = Keyword.merge(conf, config.post_config)
-    project = Project[name: name, config: conf]
-    config = config.post_config([])
-                   .update_projects(&[project|&1])
-    { :noreply, config }
-  end
-
   def handle_cast({ :post_config, value }, config) do
     { :noreply, config.update_post_config(&Keyword.merge(&1, value)) }
   end

lib/mix/test/mix/project_test.exs

@@ -18,16 +18,34 @@ defmodule Mix.ProjectTest do
 
   test "push and pop projects" do
     refute Mix.Project.get
-    Mix.Project.push(SampleProject)
+    Mix.Project.push(SampleProject, "sample")
 
     assert Mix.Project.get == SampleProject
 
-    assert Mix.Project.pop == SampleProject
+    assert Mix.Project.pop == { SampleProject, "sample" }
     assert Mix.Project.pop == nil
   after
     Mix.Project.pop
   end
 
+  test "does not allow the same project to be pushed twice" do
+    Mix.Project.push(SampleProject, "sample")
+
+    assert_raise Mix.Error, %r/Mix.ProjectTest.SampleProject from "another"/, fn ->
+      Mix.Project.push(SampleProject, "another")
+    end
+  after
+    Mix.Project.pop
+  end
+
+  test "allows nil projects to be pushed twice" do
+    Mix.Project.push nil
+    Mix.Project.push nil
+    assert Mix.Project.pop == { nil, "nofile" }
+    assert Mix.Project.pop == { nil, "nofile" }
+    assert Mix.Project.pop == nil
+  end
+
   test "retrieves configuration from projects" do
     Mix.Project.push(SampleProject)
     assert Mix.project[:hello] == "world"

lib/mix/test/mix/tasks/deps.git_test.exs

@@ -343,9 +343,9 @@ defmodule Mix.Tasks.DepsGitTest do
   end
 
   defp refresh(post_config) do
-    current = Mix.Project.pop
+    { current, file } = Mix.Project.pop
     Mix.Project.post_config(post_config)
-    Mix.Project.push(current)
+    Mix.Project.push(current, file)
   end
 
   defp get_git_repo_revs do