Improve cannot pipe error

Author: José Valim

lib/elixir/lib/macro.ex

@@ -74,7 +74,7 @@ defmodule Macro do
   def pipe(expr, call_args, position)
 
   def pipe(expr, {:&, _, _} = call_args, _integer) do
-    raise ArgumentError, "cannot pipe #{to_string expr} into #{to_string call_args}"
+    bad_pipe(expr, call_args)
   end
 
   def pipe(expr, {call, line, atom}, integer) when is_atom(atom) do
@@ -86,7 +86,12 @@ defmodule Macro do
   end
 
   def pipe(expr, call_args, _integer) do
-    raise ArgumentError, "cannot pipe #{to_string expr} into #{to_string call_args}"
+    bad_pipe(expr, call_args)
+  end
+
+  defp bad_pipe(expr, call_args) do
+    raise ArgumentError, "cannot pipe #{to_string expr} into #{to_string call_args}, " <>
+      "can only pipe into local calls foo(), remote calls Foo.bar() or anonymous functions calls foo.()"
   end
 
   @doc """

lib/elixir/test/elixir/kernel_test.exs

@@ -359,12 +359,9 @@ defmodule KernelTest do
       assert Enum.map([1, 2, 3], &(&1 |> twice |> twice)) == [4, 8, 12]
     end
 
-    test "non-call" do
+    test "anonymous functions" do
       assert  1  |> (&(&1*2)).() == 2
       assert [1] |> (&hd(&1)).() == 1
-
-      import CompileAssertion
-      assert_compile_fail ArgumentError, "cannot pipe 1 into 2", "1 |> 2"
     end
 
     defp twice(a), do: a * 2

lib/elixir/test/elixir/macro_test.exs

@@ -489,7 +489,7 @@ defmodule MacroTest do
     assert Macro.pipe(1, quote(do: foo), -1) == quote(do: foo(1))
     assert Macro.pipe(2, quote(do: foo(1)), -1) == quote(do: foo(1, 2))
 
-    assert_raise ArgumentError, "cannot pipe 1 into 2", fn ->
+    assert_raise ArgumentError, ~r"cannot pipe 1 into 2", fn ->
       Macro.pipe(1, 2, 0)
     end
   end