Json: Parser issues

[berkus]

on a following json {"body": "text\v"}
it gives
parse error at 10: parse error - unexpected '"'

dropbox/json11 gives:

unescaped (11) in string

which is correct (this is an unescaped vertical tab, disallowed by JSON std)

[nlohmann]

The scanner recognizes the malformed string and returns a parse_error token. The problem is the implementation of the unexpect function. I wanted to be clever and avoid a unexpected parse error output, so I output the text of the last token which in this case is only the opening ". I have to look into this.

[nlohmann]

With the overworked scanner in branch manual_lexer, the error message for the above code is

[json.exception.parse_error.101] parse error at 16: syntax error - invalid string: forbidden character after backspace; last read '"text\v'

[nlohmann]

The example in #551 shows that the diagnosis information got better. However, the output could be improved: last read '"\303?' does not help too much here.

[nlohmann]

The new scanner (merged yesterday) now provides the diagnosis information described in https://github.com/nlohmann/json/issues/509#issuecomment-289915749.

[berkus]

After backspace?

[nlohmann]

Ooops. Fixed this.