Add MIX_PROFILE

lib/mix/lib/mix.ex

@@ -356,6 +356,9 @@ defmodule Mix do
 
     * `MIX_PATH` - appends extra code paths
 
+    * `MIX_PROFILE` - a list of comma-separated Mix tasks to profile the time spent on
+      functions by the process running the task
+
     * `MIX_QUIET` - does not print information messages to the terminal
 
     * `MIX_REBAR3` - path to rebar3 command that overrides the one Mix installs

lib/mix/lib/mix/cli.ex

@@ -10,6 +10,10 @@ defmodule Mix.CLI do
     if env_variable_activated?("MIX_QUIET"), do: Mix.shell(Mix.Shell.Quiet)
     if env_variable_activated?("MIX_DEBUG"), do: Mix.debug(true)
 
+    if profile = System.get_env("MIX_PROFILE", "") do
+      Mix.State.put(:profile, String.split(profile, ","))
+    end
+
     case check_for_shortcuts(args) do
       :help ->
         Mix.shell().info("Mix is a build tool for Elixir")

lib/mix/lib/mix/task.ex

@@ -492,14 +492,21 @@ defmodule Mix.Task do
   end
 
   defp with_debug(task, args, proj, fun) do
-    if Mix.debug?() do
-      shell = Mix.shell()
-      shell.info(["-> Running mix ", task_to_string(task, args), project_to_string(proj)])
-      {time, res} = :timer.tc(fun)
-      shell.info(["<- Ran mix ", task, " in ", Integer.to_string(div(time, 1000)), "ms"])
-      res
-    else
-      fun.()
+    cond do
+      Mix.debug?() ->
+        shell = Mix.shell()
+        shell.info(["-> Running mix ", task_to_string(task, args), project_to_string(proj)])
+        {time, res} = :timer.tc(fun)
+        shell.info(["<- Ran mix ", task, " in ", Integer.to_string(div(time, 1000)), "ms"])
+        res
+
+      task in Mix.State.get(:profile, []) ->
+        shell = Mix.shell()
+        shell.info(["-> Profiling mix ", task_to_string(task, args), project_to_string(proj)])
+        Mix.Tasks.Profile.Eprof.profile(fun, warmup: false, set_on_spawn: false)
+
+      true ->
+        fun.()
     end
   end
 

lib/mix/lib/mix/tasks/profile.eprof.ex

@@ -181,6 +181,8 @@ defmodule Mix.Tasks.Profile.Eprof do
     * `:calls` - filters out any results with a call count lower than this
     * `:time` - filters out any results that took lower than specified (in µs)
     * `:sort` - sort the results by `:time` or `:calls` (default: `:time`)
+    * `:warmup` - if the code should be warmed up before profiling (default: `true`)
+    * `:set_on_spawn` - if newly spawned processes should be measured (default: `true`)
 
   """
   @spec profile((-> result), keyword()) :: result when result: any()
@@ -198,7 +200,8 @@ defmodule Mix.Tasks.Profile.Eprof do
     end
 
     :eprof.start()
-    {:ok, return_value} = :eprof.profile([], fun, Keyword.get(opts, :matching, {:_, :_, :_}))
+    matching = Keyword.get(opts, :matching, {:_, :_, :_})
+    {:ok, return_value} = :eprof.profile([], fun, matching, Keyword.take(opts, [:set_on_spawn]))
 
     results =
       Enum.map(:eprof.dump(), fn {pid, call_results} ->