Compute ANSI escaping lazily in Logger, closes #14248

Author: josevalim

lib/logger/lib/logger/formatter.ex

@@ -175,8 +175,7 @@ defmodule Logger.Formatter do
       warning: Keyword.get(colors, :warning, :yellow),
       notice: Keyword.get(colors, :info, :normal),
       info: Keyword.get(colors, :info, :normal),
-      debug: Keyword.get(colors, :debug, :cyan),
-      enabled: Keyword.get(colors, :enabled, IO.ANSI.enabled?())
+      debug: Keyword.get(colors, :debug, :cyan)
     }
   end
 
@@ -222,11 +221,13 @@ defmodule Logger.Formatter do
 
   defp format_fa(fun, arity), do: [Atom.to_string(fun), "/", Integer.to_string(arity)]
 
-  defp colorize(data, _level, %{enabled: false}, _md), do: data
-
-  defp colorize(data, level, %{enabled: true} = colors, md) do
-    color = md[:ansi_color] || Map.fetch!(colors, level)
-    [IO.ANSI.format_fragment(color, true), data | IO.ANSI.reset()]
+  defp colorize(data, level, colors, md) do
+    if Map.get_lazy(colors, :enabled, &IO.ANSI.enabled?/0) do
+      color = md[:ansi_color] || Map.fetch!(colors, level)
+      [IO.ANSI.format_fragment(color, true), data | IO.ANSI.reset()]
+    else
+      data
+    end
   end
 
   @doc """

lib/logger/test/logger/formatter_test.exs

@@ -64,7 +64,7 @@ defmodule Logger.FormatterTest do
         )
 
       assert %{
-               level: :warn,
+               level: :warning,
                msg: {:string, "foo"},
                meta: %{
                  mfa: {Logger.Formatter, :compile, 1}
@@ -83,7 +83,7 @@ defmodule Logger.FormatterTest do
         )
 
       assert %{
-               level: :warn,
+               level: :warning,
                msg: {:string, "message"},
                meta: %{
                  mfa: {Logger.Formatter, :compile, 1},