From c5b5aadd8ac8faeeb9e04076166df4d685633cf6 Mon Sep 17 00:00:00 2001
From: Roland Reichwein <mail@reichwein.it>
Date: Thu, 30 Dec 2021 16:39:59 +0100
Subject: Bugfix: Mapping to ISO-8859-15 was broken

---
 include/unicode.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/unicode.h b/include/unicode.h
index 1e19066..1190292 100644
--- a/include/unicode.h
+++ b/include/unicode.h
@@ -448,6 +448,7 @@ namespace unicode::detail {
                 [&](const iso_map_type::value_type& pair)
                  {
                   result.emplace(pair.second, pair.first);
+                  result.emplace(static_cast<char32_t>(static_cast<uint8_t>(pair.first)), 0); // map invalid characters to a known non-mapped value as marker
                  });
   return result;
  }
@@ -491,7 +492,7 @@ namespace unicode {
   {
    value_type value{*m_it};
 
-   if constexpr(std::addressof(Map) != std::addressof(iso_8859_1_map)) // mapping of 128 <= x <= 255 needed
+   if constexpr(std::addressof(Map) != std::addressof(iso_8859_1_map)) // mapping of 128 <= x <= 255 if needed
    {
     auto it{Map.find(value)};
     if (it != Map.end())
@@ -549,10 +550,12 @@ namespace unicode {
 
   reference operator=(const internal_type& value)
   {
-   if constexpr(std::addressof(Map) != std::addressof(iso_8859_1_map_reverse)) // mapping of 128 <= x <= 255 needed
+   if constexpr(std::addressof(Map) != std::addressof(iso_8859_1_map_reverse)) // mapping back to 128 <= x <= 255 if needed
    {
     auto it{Map.find(value)};
     if (it != Map.end()) {
+     if (it->second == 0) // marker for non-mappable character found
+      throw std::invalid_argument("Bad Unicode value to map to ISO 8859-15: "s + std::to_string(static_cast<uint32_t>(value)));
      s.push_back(it->second);
      return *this;
     }
@@ -775,7 +778,7 @@ namespace unicode {
  template<typename From, typename To, std::enable_if_t<std::is_empty<From>::value, bool> = true>
  typename To::string_type convert(const typename From::string_type& s)
  {
-  // if input type == output type, only validate and return input, is appropriate
+  // if input type == output type, only validate and return input, if appropriate
   if constexpr(sizeof(typename From::value_type) == sizeof(typename To::value_type) &&
                std::is_same_v<From, UTF<utf_iterator<typename From::value_type>, utf_back_insert_iterator<typename From::value_type>>> &&
                std::is_same_v<To, UTF<utf_iterator<typename To::value_type>, utf_back_insert_iterator<typename To::value_type>>>) {
-- 
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