Add compile time optimisation to record fields macro

Author: ericmj

lib/elixir/lib/record.ex

@@ -195,7 +195,15 @@ defmodule Record do
       Keyword.keyword?(args) ->
         create(atom, fields, args, caller)
       true ->
-        quote do: Record.__keyword__(unquote(atom), unquote(fields), unquote(args))
+        case Macro.expand(args, caller) do
+          {:{}, _, [^atom|list]} when length(list) == length(fields) ->
+            record = List.to_tuple([atom|list])
+            Macro.escape(Record.__keyword__(atom, fields, record))
+          {^atom, arg} when length(fields) == 1 ->
+            Macro.escape(Record.__keyword__(atom, fields, {atom, arg}))
+          _ ->
+            quote do: Record.__keyword__(unquote(atom), unquote(fields), unquote(args))
+        end
     end
   end
 
@@ -291,7 +299,7 @@ defmodule Record do
       [_tag|values] = Tuple.to_list(record)
       join_keyword(fields, values, [])
     else
-      msg = "expected argument to be a literal atom, literal keyword or a #{atom}() record, got runtime: #{inspect record}"
+      msg = "expected argument to be a literal atom, literal keyword or a #{inspect atom} record, got runtime: #{inspect record}"
       raise ArgumentError, msg
     end
   end

lib/elixir/test/elixir/record_test.exs

@@ -81,8 +81,9 @@ defmodule RecordTest do
 
     record = user()
     assert user(record) == [name: "José", age: 25]
+    assert user(user()) == [name: "José", age: 25]
 
-    msg = "expected argument to be a literal atom, literal keyword or a file_info() record, " <>
+    msg = "expected argument to be a literal atom, literal keyword or a :file_info record, " <>
           "got runtime: {RecordTest, \"José\", 25}"
     assert_raise ArgumentError, msg, fn ->
       file_info(record)