🐛 fixed a bug in the unget function

include/nlohmann/detail/exceptions.hpp

@@ -154,11 +154,6 @@ class parse_error : public exception
 
     static std::string position_string(const position_t& pos)
     {
-        if (pos.chars_read_total == 0)
-        {
-            return "";
-        }
-
         return " at line " + std::to_string(pos.lines_read + 1) +
                ", column " + std::to_string(pos.chars_read_current_line);
     }

include/nlohmann/detail/input/lexer.hpp

@@ -1278,13 +1278,19 @@ scan_number_done:
         next_unget = true;
 
         --position.chars_read_total;
-        --position.chars_read_current_line;
 
         // in case we "unget" a newline, we have to also decrement the lines_read
-        if (position.lines_read != 0 and position.chars_read_current_line == 0)
+        if (position.chars_read_current_line == 0)
+        {
+            if (position.lines_read > 0)
             {
                 --position.lines_read;
             }
+        }
+        else
+        {
+            --position.chars_read_current_line;
+        }
 
         if (JSON_LIKELY(current != std::char_traits<char>::eof()))
         {

single_include/nlohmann/json.hpp

@@ -795,11 +795,6 @@ class parse_error : public exception
 
     static std::string position_string(const position_t& pos)
     {
-        if (pos.chars_read_total == 0)
-        {
-            return "";
-        }
-
         return " at line " + std::to_string(pos.lines_read + 1) +
                ", column " + std::to_string(pos.chars_read_current_line);
     }
@@ -3595,13 +3590,19 @@ scan_number_done:
         next_unget = true;
 
         --position.chars_read_total;
-        --position.chars_read_current_line;
 
         // in case we "unget" a newline, we have to also decrement the lines_read
-        if (position.lines_read != 0 and position.chars_read_current_line == 0)
+        if (position.chars_read_current_line == 0)
+        {
+            if (position.lines_read > 0)
             {
                 --position.lines_read;
             }
+        }
+        else
+        {
+            --position.chars_read_current_line;
+        }
 
         if (JSON_LIKELY(current != std::char_traits<char>::eof()))
         {

test/src/unit-class_parser.cpp

@@ -1292,6 +1292,9 @@ TEST_CASE("parser class")
         CHECK(accept_helper("\"\\u01") == false);
         CHECK(accept_helper("\"\\u012") == false);
 
+        // unget of newline
+        CHECK(parser_helper("\n123\n") == 123);
+
         // invalid escapes
         for (int c = 1; c < 128; ++c)
         {