Add pretty print for DOM

[Cuda-Chen]

Add pretty print for DOM with documentation.
Currently, the indentation is fixed to four spaces.

Close #1329.

[lemire]

Lovely!

[Cuda-Chen]

Hi @lemire ,

Thanks for the reviews. As working on this PR, I was wondering about the adjustable indentation setting, i.e., some kind of pretty_formatter(3) to set the indentation to be three spaces. I tried with the following implementation but met compilation error:

// include/simdjson/dom/serialization.h

class pretty_formatter : public mini_formatter {
public:
    pretty_formatter(int n): mini_formatter(), indent_step(n) {} // a constructor for setting indentation

private:
    int indent_step = 4;
};

template <class T, class fmt = simdjson::internal::pretty_formatter>
std::string prettify(T x)  { // implement prettify with adjustable indentation setting
    simdjson::internal::string_builder<fmt> sb;
    sb.append(x);
    std::string_view answer = sb.str();
    return std::string(answer.data(), answer.size());
}


// prettify_test.cpp
pretty_formatter fmt(3); // this constructor is not included in this PR yet
simdjson::dom::element doc; // assume doc is loaded with parse JSON
auto serial = simdjson::prettify<fmt>(doc); // <-- this results in compilation error

For the adjustable indentation settings, I would like to ask whether we should implement it in this PR or not?

[lemire]

I would like to ask whether we should implement it in this PR or not?

It is fine to do multiple PRs. I don't mind reviewing 10 PRs a week from you if needed.

<-- this results in compilation error

What is the compilation error?

[jkeiser]

Ultimately, if we're doing C++ we probably want to c++-ify the interface as a formatter like cout << prettify::indent(4) << jsonthingy or some such. But that is absolutely not a thing we need to deal with in this PR :)

It's been long enough since I've been in the codebase that I'll let @lemire handle the approval here, but it looks good to me.

I would suggest removing the virtuals for now, though, and let's add them when we get a second implementation ... we might find at that point that we don't need it. (I suspect we will find that we can avoid it without complicating things :) )

[Cuda-Chen]

// include/simdjson/dom/serialization.h

class pretty_formatter : public mini_formatter {
public:
    pretty_formatter(int n): mini_formatter(), indent_step(n) {} // a constructor for setting indentation

private:
    int indent_step = 4;
};

template <class T, class fmt = simdjson::internal::pretty_formatter>
std::string prettify(T x)  { // implement prettify with adjustable indentation setting
    simdjson::internal::string_builder<fmt> sb;
    sb.append(x);
    std::string_view answer = sb.str();
    return std::string(answer.data(), answer.size());
}


// prettify_test.cpp
pretty_formatter fmt(3); // this constructor is not included in this PR yet
simdjson::dom::element doc; // assume doc is loaded with parse JSON
auto serial = simdjson::prettify<fmt>(doc); // <-- this results in compilation error

What is the compilation error?

@lemire , the compilation errors are shown as follows (seems that it fails to expand the template:

$ cmake --build .
<omit some compilation messages ...>
[ 19%] Building CXX object tests/CMakeFiles/prettify_tests.dir/prettify_tests.cpp.o
/home/jio/cpp_code/simdjson/tests/prettify_tests.cpp: In function ‘bool load_prettify(const char*)’:
/home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:37:41: error: no matching function for call to ‘prettify<fmt>(simdjson::dom::element&)’
   37 |   auto serial1 = simdjson::prettify<fmt>(doc);                                                                                      
      |                  ~~~~~~~~~~~~~~~~~~~~~~~^~~~~                                                                                       
In file included from /home/jio/cpp_code/simdjson/include/simdjson/dom.h:15,                                                                                 from /home/jio/cpp_code/simdjson/include/simdjson.h:38,
                 from /home/jio/cpp_code/simdjson/tests/cast_tester.h:4,
                 from /home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:14:
/home/jio/cpp_code/simdjson/include/simdjson/dom/serialization.h:261:13: note: candidate: ‘template<class T, class fmt> std::string simdjson
::prettify(T)’                                                                                                                                261 | std::string prettify(T x)  {                    
      |             ^~~~~~~~                                          
/home/jio/cpp_code/simdjson/include/simdjson/dom/serialization.h:261:13: note:   template argument deduction/substitution failed:
/home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:37:41: error: type/value mismatch at argument 1 in template parameter list for ‘templat
e<class T, class fmt> std::string simdjson::prettify(T)’                                                                                    
   37 |   auto serial1 = simdjson::prettify<fmt>(doc);                                                                                      
      |                  ~~~~~~~~~~~~~~~~~~~~~~~^~~~~                                                                                       
/home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:37:41: note:   expected a type, got ‘fmt’
In file included from /home/jio/cpp_code/simdjson/include/simdjson/dom.h:15,                                                                                 from /home/jio/cpp_code/simdjson/include/simdjson.h:38,
                 from /home/jio/cpp_code/simdjson/tests/cast_tester.h:4,
                 from /home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:14:
/home/jio/cpp_code/simdjson/include/simdjson/dom/serialization.h:271:13: note: candidate: ‘template<class T> std::string simdjson::prettify(
simdjson::simdjson_result<T>)’                                                                                                                271 | std::string prettify(simdjson_result<T> x) {                                                                                        
      |             ^~~~~~~~                                          
/home/jio/cpp_code/simdjson/include/simdjson/dom/serialization.h:271:13: note:   template argument deduction/substitution failed:
/home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:37:41: error: type/value mismatch at argument 1 in template parameter list for ‘templat
e<class T> std::string simdjson::prettify(simdjson::simdjson_result<T>)’                                                           
   37 |   auto serial1 = simdjson::prettify<fmt>(doc);                                                                                      
      |                  ~~~~~~~~~~~~~~~~~~~~~~~^~~~~
/home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:37:41: note:   expected a type, got ‘fmt’
/home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:40:41: error: no matching function for call to ‘prettify<fmt>(simdjson::dom::element&)’
   40 |   auto serial2 = simdjson::prettify<fmt>(doc);
      |                  ~~~~~~~~~~~~~~~~~~~~~~~^~~~~
In file included from /home/jio/cpp_code/simdjson/include/simdjson/dom.h:15,
                 from /home/jio/cpp_code/simdjson/include/simdjson.h:38,
                 from /home/jio/cpp_code/simdjson/tests/cast_tester.h:4,
                 from /home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:14:
/home/jio/cpp_code/simdjson/include/simdjson/dom/serialization.h:261:13: note: candidate: ‘template<class T, class fmt> std::string simdjson
::prettify(T)’
  261 | std::string prettify(T x)  {
      |             ^~~~~~~~
/home/jio/cpp_code/simdjson/include/simdjson/dom/serialization.h:261:13: note:   template argument deduction/substitution failed:
/home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:40:41: error: type/value mismatch at argument 1 in template parameter list for ‘templat
e<class T, class fmt> std::string simdjson::prettify(T)’
   40 |   auto serial2 = simdjson::prettify<fmt>(doc);
      |                  ~~~~~~~~~~~~~~~~~~~~~~~^~~~~
/home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:40:41: note:   expected a type, got ‘fmt’
In file included from /home/jio/cpp_code/simdjson/include/simdjson/dom.h:15,
                 from /home/jio/cpp_code/simdjson/include/simdjson.h:38,
                 from /home/jio/cpp_code/simdjson/tests/cast_tester.h:4,
                 from /home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:14:
/home/jio/cpp_code/simdjson/include/simdjson/dom/serialization.h:271:13: note: candidate: ‘template<class T> std::string simdjson::prettify(
simdjson::simdjson_result<T>)’
  271 | std::string prettify(simdjson_result<T> x) {
      |             ^~~~~~~~
/home/jio/cpp_code/simdjson/include/simdjson/dom/serialization.h:271:13: note:   template argument deduction/substitution failed:
/home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:40:41: error: type/value mismatch at argument 1 in template parameter list for ‘templat
e<class T> std::string simdjson::prettify(simdjson::simdjson_result<T>)’
   40 |   auto serial2 = simdjson::prettify<fmt>(doc);
      |                  ~~~~~~~~~~~~~~~~~~~~~~~^~~~~
/home/jio/cpp_code/simdjson/tests/prettify_tests.cpp:40:41: note:   expected a type, got ‘fmt’
gmake[2]: *** [tests/CMakeFiles/prettify_tests.dir/build.make:76: tests/CMakeFiles/prettify_tests.dir/prettify_tests.cpp.o] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:1471: tests/CMakeFiles/prettify_tests.dir/all] Error 2
gmake: *** [Makefile:166: all] Error 2

[Cuda-Chen]

Hi @lemire and @jkeiser ,
I will work on to use templates to get rid of virtual methods.

[lemire]

Running tests.

[jkeiser]

Note that if #2031 lands before this, it may affect it--however, this PR doesn't look like it'll be affected much if at all. I'll check after it lands and make a PR to be merged into this if there is anything major!