Fix Logger.Utils.truncate_n UTF-8 range for two-byte code points

Two-byte UTF-8 sequences start at U+0080 (128), not U+007F (127). The
previous guard `127..0x07FF` overlapped the single-byte clause and could
misclassify U+007F if clause order changed.

Add regression tests for U+007F/U+0080 byte boundaries.

Author: cuiweixie

lib/logger/lib/logger/utils.ex

@@ -228,7 +228,7 @@ defmodule Logger.Utils do
   end
 
   def truncate_n(int, n) when int in 0..127, do: {int, n - 1}
-  def truncate_n(int, n) when int in 127..0x07FF, do: {int, n - 2}
+  def truncate_n(int, n) when int in 128..0x07FF, do: {int, n - 2}
   def truncate_n(int, n) when int in 0x800..0xFFFF, do: {int, n - 3}
   def truncate_n(int, n) when int >= 0x10000 and is_integer(int), do: {int, n - 4}
 

lib/logger/test/logger/utils_test.exs

@@ -67,4 +67,12 @@ defmodule Logger.UtilsTest do
     long_string = String.duplicate("foo", 10_000)
     assert scan_inspect(~c"~ts", [long_string], :infinity) == {~c"~ts", [long_string]}
   end
+
+  test "truncate_n integer code points use UTF-8 byte length (U+007F 1 byte, U+0080 2 bytes)" do
+    assert Logger.Utils.truncate_n(0x7F, 1) == {0x7F, 0}
+    assert Logger.Utils.truncate_n(0x7F, 2) == {0x7F, 1}
+    assert Logger.Utils.truncate_n(0x80, 1) == {0x80, -1}
+    assert Logger.Utils.truncate_n(0x80, 2) == {0x80, 0}
+    assert Logger.Utils.truncate_n([0x7F, 0x80], 3) == {[0x7F, 0x80], 0}
+  end
 end