Soft deprecate is_exception/1 in favor of Exception.exception?/1

Author: José Valim

CHANGELOG.md

@@ -26,14 +26,15 @@
   * [System] Convert remaining functions in System to rely on char data
 
 * Soft deprecations (no warnings emitted)
-  * [Application] use Application.Behaviour is deprecated in favor of use Application
-  * [Exception] Use `Exception.message/1` to retrieve exception messages instead of `exception.message`
+  * [Application] `use Application.Behaviour` is deprecated in favor of `use Application`
+  * [Exception] `exception.message` is deprecated in favor `Exception.message/1` for retrieving exception messages
+  * [Kernel] `is_exception/1`, `is_record/1` and `is_record/2` are deprecated in favor of `Exception.exception?1`, `Record.record?/1` and `Record.record?/2`
   * [Mix] `Mix.project/0` is deprecated in favor of `Mix.Project.config/0`
-  * [Process] `Process.spawn/1`, `Process.spawn/3`, `Process.spawn_link/1`, `Process.spawn_link/3`, `Process.spawn_monitor/1`, `Process.spawn_monitor/3`, `Process.send/2` and `Process.self/0` are deprecated in favor of the ones in Kernel
+  * [Process] `Process.spawn/1`, `Process.spawn/3`, `Process.spawn_link/1`, `Process.spawn_link/3`, `Process.spawn_monitor/1`, `Process.spawn_monitor/3`, `Process.send/2` and `Process.self/0` are deprecated in favor of the ones in `Kernel`
 
 * Deprecations
   * [Kernel] `lc` and `bc` comprehensions are deprecated in favor of `for`
-  * [Macro] `Macro.safe_terms` is deprecated
+  * [Macro] `Macro.safe_terms/1` is deprecated
   * [Process] `Process.delete/0` is deprecated
   * [Regex] Deprecate `:global` option in `Regex.split/3` in favor of `parts: :infinity`
   * [String] Deprecate `:global` option in `String.split/3` in favor of `parts: :infinity`

lib/elixir/lib/exception.ex

@@ -182,6 +182,14 @@ defmodule Exception do
   @typep arity_or_args :: non_neg_integer | list
   @typep location :: Keyword.t
 
+  @doc """
+  Returns true if the given argument is an exception.
+  """
+  def exception?(exception) do
+    is_tuple(exception) and tuple_size(exception) > 1 and
+      :erlang.element(2, exception) == :__exception__
+  end
+
   @doc """
   Gets the message for an exception.
   """
@@ -218,13 +226,15 @@ defmodule Exception do
   def normalize(kind, payload, stacktrace \\ nil)
 
   def normalize(:error, exception, stacktrace) do
-    normalize_error(exception, stacktrace)
+    if exception?(exception) do
+      exception
+    else
+      normalize_error(exception, stacktrace)
+    end
   end
 
-  def normalize(_kind, payload, _stacktrace), do: payload
-
-  defp normalize_error(exception, _stacktrace) when is_exception(exception) do
-    exception
+  def normalize(_kind, payload, _stacktrace) do
+    payload
   end
 
   defp normalize_error(:badarg, _stacktrace) do
@@ -298,7 +308,7 @@ defmodule Exception do
   def format_banner(kind, exception, stacktrace \\ nil)
 
   def format_banner(:error, exception, stacktrace) do
-    exception = normalize_error(exception, stacktrace)
+    exception = normalize(:error, exception, stacktrace)
     "** (" <> inspect(exception.__record__(:name)) <> ") " <> message(exception)
   end
 

lib/elixir/lib/kernel.ex

@@ -1776,6 +1776,7 @@ defmodule Kernel do
 
   """
   defmacro is_exception(thing) do
+    # IO.write :stderr, "Kernel.is_exception/1 is deprecated, please use Exception.exception?/1 instead\n#{Exception.format_stacktrace}"
     case Macro.Env.in_guard?(__CALLER__) do
       true ->
         quote do
@@ -1806,6 +1807,7 @@ defmodule Kernel do
 
   """
   defmacro is_record(thing, kind) do
+    # IO.write :stderr, "Kernel.is_record/2 is deprecated, please use Record.record?/2 instead\n#{Exception.format_stacktrace}"
     case Macro.Env.in_guard?(__CALLER__) do
       true ->
         quote do
@@ -1825,6 +1827,7 @@ defmodule Kernel do
   Checks if the given argument is a record.
   """
   defmacro is_record(thing) do
+    # IO.write :stderr, "Kernel.is_record/1 is deprecated, please use Record.record?/1 instead\n#{Exception.format_stacktrace}"
     case Macro.Env.in_guard?(__CALLER__) do
       true ->
         quote do

lib/elixir/test/elixir/exception_test.exs

@@ -19,11 +19,10 @@ defmodule Kernel.ExceptionTest do
            [file: ^file, line: 12]} = stacktrace
   end
 
-  test "is_exception" do
-    assert is_exception(RuntimeError.new)
-    refute is_exception(empty_tuple)
-    refute is_exception(a_tuple)
-    refute is_exception(a_list)
+  test "exception?" do
+    assert Exception.exception?(RuntimeError.new)
+    refute Exception.exception?({})
+    refute Exception.exception?(%{})
   end
 
   test "message" do
@@ -220,8 +219,4 @@ defmodule Kernel.ExceptionTest do
     assert ErlangError.new(original: :sample) |> message ==
            "erlang error: :sample"
   end
-
-  defp empty_tuple, do: {}
-  defp a_tuple, do: {:foo, :bar, :baz}
-  defp a_list,  do: [ :foo, :bar, :baz ]
 end