Unify common code for different output styles

[mgreter]

Currently we only support nested and compressed output. But these currently do not share a common parent class. IMO we should create such a base class for all output styles, which will implement all common parts.

#717: Main reasons (beside DRY):

• Abstract the output buffer and provide a simple API
• Source-maps should be created automatically
• The UTF-8 charset should be added automatically
• Makes it easier to implement other output styles

I already made some experiments when implementing the charset feature.
It should be usable as a starting point, if someone else wants to start with it:

#file: output.hpp
#define SASS_OUTPUT

#ifndef SASS_OPERATION
#include "operation.hpp"
#endif

#ifndef SASS_CONTEXT
#include "context.hpp"
#endif

#include <string>

namespace Sass {
  using namespace std;
  struct Context;

  template<typename T>
  class Output : public Operation_CRTP<void, T> {
    // import all the class-specific methods and override as desired
    using Operation_CRTP<void, T>::operator();

  protected:
    Context* ctx;
    string buffer;
    string rendered_imports;
    bool seen_utf8;

    virtual void fallback_impl(AST_Node* n) = 0;

  public:

    Output(Context* ctx = 0)
    : ctx(ctx),
      buffer(""),
      rendered_imports(""),
      seen_utf8(false)
    { }
    virtual ~Output() { };

    string get_buffer()
    {
      return rendered_imports + buffer;
    }

    // append some text or token to the buffer
    // it is the main function for source-mapping
    void append_buffer(const string& data)
    {
      // search for unicode char
      for(const char& chr : data) {
        // abort clause
        if (seen_utf8) break;
        // skip all normal ascii chars
        if (chr >= 0 && chr < 128) continue;
        // prepend charset to buffer
        buffer = "@charset \"UTF-8\";\n" + buffer;
        // singleton
        seen_utf8 = true;
      }
      // add to buffer
      buffer += data;
      // account for data in source-maps
      ctx->source_map.update_column(data);
    }

  };

}

I was not able to implement this outside the header, which is probably because my c++ template foo is not very good. Maybe someone else knows if this is the only/right way?

[am11]

👍 abstract classes FTW!

Speaking of refactoring the code, would it make sense to also restructure the repo: separate .cs and .cpps from .hs and .hpps like so:

root
   \
    libsass
        \
        sources
            \ 
             {  all source files go here, could have subdirectories }
        \
        headers 
            \ 
             {  all header files go here, could have subdirectories matching those under sources }

This way the README would be visible without scrolling down the repo's main page. 😄

[mgreter]

This issue should (hopefully) be addressed/fixed by #792.
I have created a common Output class from which nested/compressed inherit!