Do not consider remote typespecs as a compile-time dependency (#5093)

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

lib/elixir/lib/kernel/typespec.ex

@@ -777,6 +777,8 @@ defmodule Kernel.Typespec do
   end
 
   defp typespec({:%, _, [name, {:%{}, meta, fields}]}, vars, caller) do
+    # We cannot set a function name to avoid tracking
+    # as a compile time dependency, because for structs it actually is one.
     module = Macro.expand(name, caller)
 
     struct =
@@ -813,6 +815,8 @@ defmodule Kernel.Typespec do
   end
 
   defp typespec({:record, meta, [atom, fields]}, vars, caller) do
+    # We cannot set a function name to avoid tracking
+    # as a compile time dependency because for records it actually is one.
     case Macro.expand({atom, [], [{atom, [], []}]}, caller) do
       keyword when is_list(keyword) ->
         types =
@@ -883,7 +887,9 @@ defmodule Kernel.Typespec do
 
   # Handle remote calls
   defp typespec({{:., meta, [remote, name]}, _, args} = orig, vars, caller) do
-    remote = Macro.expand remote, caller
+    # We set a function name to avoid tracking
+    # aliases in typespecs as compile time dependencies.
+    remote = Macro.expand remote, %{caller | function: {:typespec, 0}}
     unless is_atom(remote) do
       compile_error(caller, "invalid remote in typespec: #{Macro.to_string(orig)}")
     end

lib/mix/test/mix/tasks/compile.elixir_test.exs

@@ -231,4 +231,28 @@ defmodule Mix.Tasks.Compile.ElixirTest do
       assert_received {:mix_shell, :info, ["Compiled lib/a.ex"]}
     end
   end
+
+  test "does not treat remote typespecs as compile time dependencies" do
+    in_fixture "no_mixfile", fn ->
+      File.write!("lib/b.ex", """
+      defmodule B do
+        @type t :: A.t
+      end
+      """)
+
+      assert Mix.Tasks.Compile.Elixir.run(["--verbose"]) == :ok
+      assert_received {:mix_shell, :info, ["Compiled lib/a.ex"]}
+      assert_received {:mix_shell, :info, ["Compiled lib/b.ex"]}
+
+      Mix.shell.flush
+      purge [A, B]
+
+      future = {{2020, 1, 1}, {0, 0, 0}}
+      File.touch!("lib/a.ex", future)
+      Mix.Tasks.Compile.Elixir.run ["--verbose"]
+
+      assert_received {:mix_shell, :info, ["Compiled lib/a.ex"]}
+      refute_received {:mix_shell, :info, ["Compiled lib/b.ex"]}
+    end
+  end
 end