Ensure we consolidate only when there was a change

Author: José Valim

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

@@ -60,9 +60,11 @@ defmodule Mix.Tasks.Compile do
   def run(args) do
     Mix.Project.get!
     Mix.Task.run "loadpaths", args
+
     res = Mix.Task.run "compile.all", args
+    res = if :ok in List.wrap(res), do: :ok, else: :noop
 
-    if consolidate_protocols?() do
+    if res == :ok && consolidate_protocols?() do
       Mix.Task.run "compile.protocols", args
     end
 

lib/mix/test/mix/tasks/compile_test.exs

@@ -52,6 +52,9 @@ defmodule Mix.Tasks.CompileTest do
       assert_received {:mix_shell, :info, ["Consolidated Enumerable"]}
       assert File.regular? "_build/dev/consolidated/Elixir.Enumerable.beam"
 
+      assert Mix.Tasks.Compile.run([]) == :noop
+      refute_received {:mix_shell, :info, ["Consolidated Enumerable"]}
+
       assert Mix.Tasks.App.Start.run([]) == :ok
       assert Protocol.consolidated?(Enumerable)
     end