UDT serialization of paths

Author: grisumbras

include/boost/json/impl/serializer.hpp

@@ -767,6 +767,53 @@ write_impl(optional_conversion_tag, writer& w, stream& ss)
     return done;
 }
 
+template<class T, bool StackEmpty>
+BOOST_FORCEINLINE
+bool
+write_impl(path_conversion_tag, writer& w, stream& ss)
+{
+#if defined(_MSC_VER)
+# pragma warning( push )
+# pragma warning( disable : 4127 )
+#endif
+    if(StackEmpty || w.st_.empty())
+#if defined(_MSC_VER)
+# pragma warning( pop )
+#endif
+    {
+        BOOST_ASSERT( w.p_ );
+        T const* pt = reinterpret_cast<T const*>(w.p_);
+
+        std::string const s = pt->generic_string();
+        w.cs0_ = { s.data(), s.size() };
+        if(BOOST_JSON_LIKELY( write_string(w, ss) ))
+            return true;
+
+        std::size_t const used = w.cs0_.used( s.data() );
+        w.st_.push( used );
+        w.st_.push( std::move(s) );
+        return false;
+    }
+    else
+    {
+        std::string s;
+        std::size_t used;
+        w.st_.pop( s );
+        w.st_.pop( used );
+
+        w.cs0_ = { s.data(), s.size() };
+        w.cs0_.skip(used);
+
+        if(BOOST_JSON_LIKELY( resume_string(w, ss) ))
+            return true;
+
+        used = w.cs0_.used( s.data() );
+        w.st_.push( used );
+        w.st_.push( std::move(s) );
+        return false;
+    }
+}
+
 template<class T, bool StackEmpty>
 bool
 write_impl(writer& w, stream& ss)

test/serializer.cpp

@@ -21,6 +21,10 @@
 #include <vector>
 #include <limits.h>
 
+#ifndef BOOST_NO_CXX17_HDR_FILESYSTEM
+#include <filesystem>
+#endif // BOOST_NO_CXX17_HDR_FILESYSTEM
+
 #include "parse-vectors.hpp"
 #include "test.hpp"
 #include "test_suite.hpp"
@@ -866,6 +870,27 @@ class serializer_test
             check_udt( o, "2315" );
         }
 #endif // BOOST_NO_CXX17_HDR_OPTIONAL
+#ifndef BOOST_NO_CXX17_HDR_FILESYSTEM
+        {
+            std::filesystem::path p = "from/here";
+            check_udt(p, R"("from/here")");
+
+            p = "to/there";
+            check_udt(p, R"("to/there")");
+
+            p = "";
+            check_udt(p, R"("")");
+
+            p = "c:/";
+            check_udt(p, R"("c:/")");
+
+            p = "..";
+            check_udt(p, R"("..")");
+
+            p = "../";
+            check_udt(p, R"("../")");
+        }
+#endif // BOOST_NO_CXX17_HDR_FILESYSTEM
     }
 
     void