Deprecate x.Alias syntax

Author: José Valim

lib/elixir/lib/kernel/special_forms.ex

@@ -343,28 +343,9 @@ defmodule Kernel.SpecialForms do
 
   Note that `Kernel."HELLO"` will be treated as a remote call and not an alias.
   This choice was done so every time single- or double-quotes are used, we have
-  a remote call irregardless of the quote contents. This decision is also reflected
+  a remote call regardless of the quote contents. This decision is also reflected
   in the quoted expressions discussed below.
 
-  ## Runtime (dynamic) behaviour
-
-  The result returned by `.` is always specified by the right-side:
-
-      iex> x = String
-      iex> x.downcase("FOO")
-      "foo"
-      iex> x.Sample
-      String.Sample
-
-  In case the right-side is also dynamic, `.`'s behaviour can be reproduced
-  at runtime via `apply/3` and `Module.concat/2`:
-
-      iex> apply(:erlang, :+, [1,2])
-      3
-
-      iex> Module.concat(Kernel, Sample)
-      Kernel.Sample
-
   ## Quoted expression
 
   When `.` is used, the quoted expression may take two distinct
@@ -1327,22 +1308,13 @@ defmodule Kernel.SpecialForms do
 
   On the other hand, aliases holds some properties:
 
-    1. The head element of aliases can be any term.
+    1. The head element of aliases can be any term that must expand to
+       an atom at compilation time.
 
     2. The tail elements of aliases are guaranteed to always be atoms.
 
     3. When the head element of aliases is the atom `:Elixir`, no expansion happen.
 
-    4. When the head element of aliases is not an atom, it is expanded at runtime:
-
-           quote do: some_var.Foo
-           {:__aliases__, [], [{:some_var, [], Elixir}, :Foo]}
-
-       Since `some_var` is not available at compilation time, the compiler
-       expands such expression to:
-
-           Module.concat [some_var, Foo]
-
   """
   defmacro __aliases__(args)
 

lib/elixir/src/elixir_exp.erl

@@ -66,6 +66,8 @@ expand({'__aliases__', _, _} = Alias, E) ->
           elixir_lexical:record_remote(Receiver, ?m(E, lexical_tracker)),
           {Receiver, EA};
         false ->
+          elixir_errors:warn(?m(E, line), ?m(E, file), io_lib:format("an alias must expand to an atom "
+            "at compilation time but got ~ts", ['Elixir.Macro':to_string(hd(EAliases))])),
           {{{'.', [], [elixir_aliases, concat]}, [], [EAliases]}, EA}
       end
   end;

lib/elixir/test/elixir/kernel/expansion_test.exs

@@ -55,11 +55,6 @@ defmodule Kernel.ExpansionTest do
     assert expand_env(quote(do: World), __ENV__) |> elem(0) == :"Elixir.Source"
   end
 
-  test "__aliases__: expands to elixir_aliases on runtime" do
-    assert expand(quote do: hello.World) ==
-           quote do: :elixir_aliases.concat([hello(), :World])
-  end
-
   ## =
 
   test "=: sets context to match" do

lib/elixir/test/erlang/module_test.erl

@@ -90,9 +90,6 @@ nesting_test() ->
 dot_alias_test() ->
   {'Elixir.Foo.Bar.Baz', _} = eval("Foo.Bar.Baz").
 
-dot_dyn_alias_test() ->
-  {'Elixir.Foo.Bar.Baz', _} = eval("a = Foo.Bar; a.Baz").
-
 single_ref_test() ->
   {'Elixir.Foo', _} = eval("Foo"),
   {'Elixir.Foo', _} = eval("Elixir.Foo").