From 371d8e2ee044181b5c3fe36658c6f991277a678a Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@fb.com>
Date: Sun, 22 Aug 2021 07:38:22 -0700
Subject: [PATCH] Escape Unicode

---
 include/fmt/ranges.h | 8 +++++++-
 test/ranges-test.cc  | 6 ++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/fmt/ranges.h b/include/fmt/ranges.h
index 8ee5a0ee..ab60f805 100644
--- a/include/fmt/ranges.h
+++ b/include/fmt/ranges.h
@@ -304,9 +304,15 @@ auto write_range_entry(OutputIt out, basic_string_view<Char> str) -> OutputIt {
       *out++ = '\\';
       break;
     default:
+      if (is_utf8() && escape.cp > 0xffff) {
+        out = format_to(out, "\\U{:08x}", escape.cp);
+        continue;
+      }
       for (Char escape_char : basic_string_view<Char>(
                escape.begin, to_unsigned(escape.end - escape.begin))) {
-        out = format_to(out, "\\x{:02x}", escape_char);
+        out = format_to(
+            out, "\\x{:02x}",
+            static_cast<typename std::make_unsigned<Char>::type>(escape_char));
       }
       continue;
     }
diff --git a/test/ranges-test.cc b/test/ranges-test.cc
index 2d6ce814..1addbf5f 100644
--- a/test/ranges-test.cc
+++ b/test/ranges-test.cc
@@ -268,4 +268,10 @@ TEST(ranges_test, escape_string) {
   EXPECT_EQ(fmt::format("{}", vec{"\n\r\t\"\\"}), "[\"\\n\\r\\t\\\"\\\\\"]");
   EXPECT_EQ(fmt::format("{}", vec{"\x07"}), "[\"\\x07\"]");
   EXPECT_EQ(fmt::format("{}", vec{"\x7f"}), "[\"\\x7f\"]");
+
+  // Unassigned Unicode code points.
+  if (fmt::detail::is_utf8()) {
+    EXPECT_EQ(fmt::format("{}", vec{"\xf0\xaa\x9b\x9e"}), "[\"\\U0002a6de\"]");
+    EXPECT_EQ(fmt::format("{}", vec{"\xf4\x8f\xbf\xbf"}), "[\"\\U0010ffff\"]");
+  }
 }