⚗️ try minimal example

test/src/unit-disabled_exceptions.cpp

@@ -52,6 +52,81 @@ class sax_no_exception : public nlohmann::detail::json_sax_dom_parser<json>
 
 std::string* sax_no_exception::error_string = nullptr;
 
+//
+#include <cstddef> // size_t
+#include <exception> // exception
+#include <stdexcept> // runtime_error
+#include <string> // to_string
+#include <vector> // vector
+
+//
+namespace nlohmann
+{
+namespace detail2
+{
+
+struct position_t
+{
+    std::size_t chars_read_total = 0;
+    std::size_t chars_read_current_line = 0;
+    std::size_t lines_read = 0;
+
+    constexpr operator size_t() const
+    {
+        return chars_read_total;
+    }
+};
+
+
+class exception : public std::exception
+{
+  public:
+    const char* what() const noexcept override
+    {
+        return m.what();
+    }
+
+    const int id;
+
+  protected:
+    exception(int id_, const char* what_arg) : id(id_), m(what_arg) {}
+
+    static std::string name(const std::string& ename, int id_)
+    {
+        return "[json.exception." + ename + "." + std::to_string(id_) + "] ";
+    }
+
+  private:
+    std::runtime_error m;
+};
+
+class parse_error : public exception
+{
+  public:
+    static parse_error create(int id_, const position_t& pos, const std::string& what_arg)
+    {
+        std::string w = exception::name("parse_error", id_) + "parse error" +
+                        position_string(pos) + ": " + what_arg;
+        return parse_error(id_, pos.chars_read_total, w.c_str());
+    }
+
+    const std::size_t byte;
+
+  private:
+    parse_error(int id_, std::size_t byte_, const char* what_arg)
+        : exception(id_, what_arg), byte(byte_) {}
+
+    static std::string position_string(const position_t& pos)
+    {
+        return " at line " + std::to_string(pos.lines_read + 1) +
+               ", column " + std::to_string(pos.chars_read_current_line);
+    }
+};
+
+}  // namespace detail
+}  // namespace nlohmann
+//
+
 TEST_CASE("Tests with disabled exceptions")
 {
     SECTION("issue #2824 - encoding of json::exception::what()")
@@ -60,7 +135,18 @@ TEST_CASE("Tests with disabled exceptions")
         sax_no_exception sax(j);
 
         CHECK (!json::sax_parse("xyz", &sax));
-        CHECK(*sax_no_exception::error_string == "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - invalid literal; last read: 'x'");
+        //CHECK(*sax_no_exception::error_string == "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - invalid literal; last read: 'x'");
         delete sax_no_exception::error_string; // NOLINT(cppcoreguidelines-owning-memory)
     }
+
+    SECTION("test")
+    {
+        nlohmann::detail2::position_t pos;
+        pos.chars_read_total = 100;
+        pos.chars_read_current_line = 50;
+        pos.lines_read = 1;
+
+        auto error = nlohmann::detail2::parse_error::create(100, pos, "foo");
+        CHECK(std::string(error.what()) == "[json.exception.parse_error.100] parse error at line 2, column 50: foo");
+    }
 }