Load mix deps only when there is a need to use them

This helps speed up peformance to many tasks. Tasks like
clean, help and compile --list must now explicitly call
loadpaths with checks disabled so they can still show
data coming from dependencies but without causing crashes.

lib/mix/lib/mix/cli.ex

@@ -51,11 +51,7 @@ defmodule Mix.CLI do
 
   defp run_task(name, args) do
     try do
-      if Mix.Project.get do
-        Mix.Task.run "loadconfig"
-        Mix.Task.run "loadpaths", ["--no-elixir-version-check", "--no-deps-check"]
-        Mix.Task.reenable "loadpaths"
-      end
+      Mix.Task.run "loadconfig"
 
       # If the task is not available, let's try to
       # compile the repository and then run it again.

lib/mix/lib/mix/dep/lock.ex

@@ -33,7 +33,7 @@ defmodule Mix.Dep.Lock do
   Returns the elixir version in the lock manifest unless is an umbrella app.
   """
   def elixir_vsn() do
-    unless Mix.Project.umbrella?, do: elixir_vsn(Mix.Project.manifest_path)
+    elixir_vsn(Mix.Project.manifest_path)
   end
 
   @doc """

lib/mix/lib/mix/project.ex

@@ -18,7 +18,7 @@ defmodule Mix.Project do
   After being defined, the configuration for this project can be read
   as `Mix.Project.config/0`. Notice that `config/0` won't fail if a
   project is not defined; this allows many mix tasks to work
-  even without a project.
+  without a project.
 
   In case the developer needs a project or wants to access a special
   function in the project, the developer can call `Mix.Project.get!/0`

lib/mix/lib/mix/tasks/app.start.ex

@@ -18,6 +18,7 @@ defmodule Mix.Tasks.App.Start do
 
   """
   def run(args) do
+    Mix.Project.get!
     Mix.Task.run "loadpaths", ["--no-readd"|args]
 
     unless "--no-compile" in args do

lib/mix/lib/mix/tasks/clean.ex

@@ -18,14 +18,15 @@ defmodule Mix.Tasks.Clean do
   """
 
   def run(args) do
+    Mix.Project.get!
+    loadpaths!
+
     {opts, _, _} = OptionParser.parse(args)
 
-    _ = for compiler <- Mix.Tasks.Compile.compilers() do
-      module = Mix.Task.get!("compile.#{compiler}")
-      if function_exported?(module, :clean, 0) do
-        module.clean
-      end
-    end
+    _ = for compiler <- Mix.Tasks.Compile.compilers(),
+            module = Mix.Task.get("compile.#{compiler}"),
+            function_exported?(module, :clean, 0),
+            do: module.clean
 
     if opts[:all] do
       Mix.Task.run("deps.clean", args)
@@ -41,4 +42,10 @@ defmodule Mix.Tasks.Clean do
       |> Enum.each(&File.rm_rf/1)
     end
   end
+
+  # Loadpaths without checks because compilers may be defined in deps.
+  defp loadpaths! do
+    Mix.Task.run "loadpaths", ["--no-elixir-version-check", "--no-deps-check"]
+    Mix.Task.reenable "loadpaths"
+  end
 end

lib/mix/lib/mix/tasks/compile.ex

@@ -23,6 +23,7 @@ defmodule Mix.Tasks.Compile do
 
   """
   def run(["--list"]) do
+    loadpaths!
     Mix.Task.load_all
 
     shell   = Mix.shell
@@ -49,6 +50,7 @@ defmodule Mix.Tasks.Compile do
   end
 
   def run(args) do
+    Mix.Project.get!
     Mix.Task.run "loadpaths", ["--no-readd"|args]
 
     res =
@@ -61,6 +63,12 @@ defmodule Mix.Tasks.Compile do
     if Enum.any?(res, &(:ok in &1)), do: :ok, else: :noop
   end
 
+  # Loadpaths without checks because compilers may be defined in deps.
+  defp loadpaths! do
+    Mix.Task.run "loadpaths", ["--no-elixir-version-check", "--no-deps-check"]
+    Mix.Task.reenable "loadpaths"
+  end
+
   @doc """
   Returns all compilers.
   """

lib/mix/lib/mix/tasks/deps.check.ex

@@ -78,7 +78,7 @@ defmodule Mix.Tasks.Deps.Check do
       paths = Mix.Project.build_path(config)
               |> Path.join("lib/*/ebin")
               |> Path.wildcard
-              |> List.delete(not Mix.Project.umbrella? && Mix.Project.compile_path(config))
+              |> List.delete(config[:app] && Mix.Project.compile_path(config))
 
       to_prune = Enum.reduce(all, paths, &(&2 -- Mix.Dep.load_paths(&1)))
 

lib/mix/lib/mix/tasks/deps.clean.ex

@@ -15,7 +15,7 @@ defmodule Mix.Tasks.Deps.Clean do
   @switches [unlock: :boolean, all: :boolean, only: :string]
 
   def run(args) do
-    Mix.Project.get! # Require the project to be available
+    Mix.Project.get!
     {opts, args, _} = OptionParser.parse(args, switches: @switches)
 
     cond do

lib/mix/lib/mix/tasks/deps.compile.ex

@@ -28,8 +28,7 @@ defmodule Mix.Tasks.Deps.Compile do
                          format_dep: 1, make?: 1, mix?: 1, rebar?: 1]
 
   def run(args) do
-    Mix.Project.get! # Require the project to be available
-
+    Mix.Project.get!
     case OptionParser.parse(args) do
       {_, [], _} ->
         compile(Enum.filter(loaded(env: Mix.env), &compilable?/1))

lib/mix/lib/mix/tasks/deps.ex

@@ -96,7 +96,7 @@ defmodule Mix.Tasks.Deps do
 
   """
   def run(args) do
-    Mix.Project.get! # Require the project to be available
+    Mix.Project.get!
     {opts, _, _} = OptionParser.parse(args)
 
     if opts[:all] do

lib/mix/lib/mix/tasks/deps.get.ex

@@ -13,7 +13,7 @@ defmodule Mix.Tasks.Deps.Get do
     * `--only`  - only fetch dependencies for given environment
   """
   def run(args) do
-    Mix.Project.get! # Require the project to be available
+    Mix.Project.get!
     {opts, _, _} = OptionParser.parse(args, switches: [quiet: :boolean, only: :string])
 
     # Fetch all deps by default unless --only is given

lib/mix/lib/mix/tasks/deps.unlock.ex

@@ -11,7 +11,7 @@ defmodule Mix.Tasks.Deps.Unlock do
   """
 
   def run(args) do
-    Mix.Project.get! # Require the project to be available
+    Mix.Project.get!
     {opts, args, _} = OptionParser.parse(args, switches: [all: :boolean])
 
     cond do

lib/mix/lib/mix/tasks/deps.update.ex

@@ -17,7 +17,7 @@ defmodule Mix.Tasks.Deps.Update do
     * `--only` - only fetch dependencies for given environment
   """
   def run(args) do
-    Mix.Project.get! # Require the project to be available
+    Mix.Project.get!
     {opts, rest, _} = OptionParser.parse(args, switches: [all: :boolean, only: :string])
 
     # Fetch all deps by default unless --only is given

lib/mix/lib/mix/tasks/escript.build.ex

@@ -72,10 +72,8 @@ defmodule Mix.Tasks.Escript.Build do
 
   """
   def run(args) do
-    {opts, _, _} = OptionParser.parse(args, switches: [force: :boolean, compile: :boolean])
-
-    # Require the project to be available
     Mix.Project.get!
+    {opts, _, _} = OptionParser.parse(args, switches: [force: :boolean, compile: :boolean])
 
     if Keyword.get(opts, :compile, true) do
       Mix.Task.run :compile, args

lib/mix/lib/mix/tasks/help.ex

@@ -37,6 +37,8 @@ defmodule Mix.Tasks.Help do
   """
 
   def run([]) do
+    loadpaths!
+
     shell   = Mix.shell
     modules = Mix.Task.load_all()
 
@@ -59,6 +61,8 @@ defmodule Mix.Tasks.Help do
   end
 
   def run(["--names"]) do
+    loadpaths!
+
     tasks =
       Mix.Task.load_all()
       |> Enum.map(&Mix.Task.task_name/1)
@@ -74,6 +78,8 @@ defmodule Mix.Tasks.Help do
   end
 
   def run([task]) do
+    loadpaths!
+
     module = Mix.Task.get!(task)
     doc    = Mix.Task.moduledoc(module) || "There is no documentation for this task"
     opts   = Application.get_env(:mix, :colors)
@@ -94,6 +100,12 @@ defmodule Mix.Tasks.Help do
     Mix.raise "Unexpected arguments, expected `mix help` or `mix help TASK`"
   end
 
+  # Loadpaths without checks because tasks may be defined in deps.
+  defp loadpaths! do
+    Mix.Task.run "loadpaths", ["--no-elixir-version-check", "--no-deps-check"]
+    Mix.Task.reenable "loadpaths"
+  end
+
   defp ansi_docs?(opts) do
     if Keyword.has_key?(opts, :enabled) do
       opts[:enabled]

lib/mix/lib/mix/tasks/loadpaths.ex

@@ -23,7 +23,9 @@ defmodule Mix.Tasks.Loadpaths do
       load_deps(config, args)
     end
 
-    load_project(config, args)
+    if config[:app] do
+      load_project(config, args)
+    end
 
     unless "--no-readd" in args do
       Code.readd_paths()
@@ -53,12 +55,12 @@ defmodule Mix.Tasks.Loadpaths do
     Mix.Project.build_path(config)
     |> Path.join("lib/*/ebin")
     |> Path.wildcard
-    |> List.delete(not Mix.Project.umbrella? && Mix.Project.compile_path(config))
+    |> List.delete(config[:app] && Mix.Project.compile_path(config))
     |> Enum.each(&Code.prepend_path/1)
   end
 
   defp load_project(config, _args) do
-    # Force recompile if we have a version mismatch
+    # Force recompile if we have an app and a version mismatch
     old_vsn = Mix.Dep.Lock.elixir_vsn
     if old_vsn && old_vsn != System.version, do: Mix.Dep.Lock.touch
 

lib/mix/lib/mix/tasks/run.ex

@@ -39,9 +39,6 @@ defmodule Mix.Tasks.Run do
       switches: [parallel_require: :keep, require: :keep, eval: :keep, config: :keep,
                  halt: :boolean, compile: :boolean, deps_check: :boolean, start: :boolean])
 
-    # Require the project to be available
-    Mix.Project.get!
-
     {file, argv} =
       case {Keyword.has_key?(opts, :eval), head} do
         {true, _}  -> {nil, head}