Improve sourcemap output for prepended texts

Fixes #879
Should work for all prepended texts (like top-comments)

ast.hpp

@@ -44,6 +44,7 @@
 #include "ast_def_macros.hpp"
 #include "ast_fwd_decl.hpp"
 #include "to_string.hpp"
+#include "source_map.hpp"
 
 #include "sass.h"
 #include "sass_values.h"

emitter.cpp

@@ -85,10 +85,17 @@ namespace Sass {
     }
   }
 
+  // prepend some text or token to the buffer
+  void Emitter::prepend_output(const OutputBuffer& output)
+  {
+    wbuf.smap.prepend(output);
+    wbuf.buffer = output.buffer + wbuf.buffer;
+  }
+
   // prepend some text or token to the buffer
   void Emitter::prepend_string(const string& text)
   {
-    // update source-map for new text
+    wbuf.smap.prepend(Offset(text));
     wbuf.buffer = text + wbuf.buffer;
   }
 
@@ -104,12 +111,12 @@ namespace Sass {
       // add to buffer
       wbuf.buffer += out;
       // account for data in source-maps
-      wbuf.smap.update_column(out);
+      wbuf.smap.append(Offset(out));
     } else {
       // add to buffer
       wbuf.buffer += text;
       // account for data in source-maps
-      wbuf.smap.update_column(text);
+      wbuf.smap.append(Offset(text));
     }
   }
 

emitter.hpp

@@ -9,17 +9,6 @@ namespace Sass {
   class Context;
   using namespace std;
 
-  class OutputBuffer {
-    public:
-      OutputBuffer(void)
-      : buffer(""),
-        smap()
-      { }
-    public:
-      string buffer;
-      SourceMap smap;
-  };
-
   class Emitter {
 
     public:
@@ -31,6 +20,7 @@ namespace Sass {
     public:
       const string buffer(void) { return wbuf.buffer; }
       const SourceMap smap(void) { return wbuf.smap; }
+      const OutputBuffer output(void) { return wbuf; }
       // proxy methods for source maps
       void add_source_index(size_t idx);
       void set_filename(const string& str);
@@ -64,6 +54,7 @@ namespace Sass {
       void flush_schedules(void);
       // prepend some text or token to the buffer
       void prepend_string(const string& text);
+      void prepend_output(const OutputBuffer& out);
       // append some text or token to the buffer
       void append_string(const string& text);
       // append some white-space only text

output.cpp

@@ -44,9 +44,8 @@ namespace Sass {
 
     // flush scheduled outputs
     inspect.finalize();
-    // create combined buffer string
-    wbuf.buffer = inspect.buffer()
-                + this->buffer();
+    // prepend buffer on top
+    prepend_output(inspect.output());
     // make sure we end with a linefeed
     if (!ends_with(wbuf.buffer, ctx->linefeed)) {
       // if the output is not completely empty

position.cpp

@@ -4,6 +4,18 @@ namespace Sass {
 
   using namespace std;
 
+  Offset::Offset(const char* string)
+  : line(0), column(0)
+  {
+    *this = inc(string, string + strlen(string));
+  }
+
+  Offset::Offset(const string& text)
+  : line(0), column(0)
+  {
+    *this = inc(text.c_str(), text.c_str() + text.size());
+  }
+
   Offset::Offset(const size_t line, const size_t column)
   : line(line), column(column) { }
 
@@ -34,7 +46,12 @@ namespace Sass {
     return line != pos.line || column != pos.column;
   }
 
-  const Offset Offset::operator+ (const Offset &off) const
+  void Offset::operator+= (const Offset &off)
+  {
+    *this = Offset(line + off.line, off.line > 0 ? off.column : off.column + column);
+  }
+
+  Offset Offset::operator+ (const Offset &off) const
   {
     return Offset(line + off.line, off.line > 0 ? off.column : off.column + column);
   }
@@ -67,7 +84,7 @@ namespace Sass {
   Position Position::inc(const char* begin, const char* end) const
   {
     Offset offset(line, column);
-    offset.inc(begin, end);
+    offset = offset.inc(begin, end);
     return Position(file, offset);
   }
 
@@ -81,6 +98,11 @@ namespace Sass {
     return file == pos.file || line != pos.line || column != pos.column;
   }
 
+  void Position::operator+= (const Offset &off)
+  {
+    *this = Position(file, line + off.line, off.line > 0 ? off.column : off.column + column);
+  }
+
   const Position Position::operator+ (const Offset &off) const
   {
     return Position(file, line + off.line, off.line > 0 ? off.column : off.column + column);

position.hpp

@@ -14,15 +14,18 @@ namespace Sass {
   class Offset {
 
     public: // c-tor
+      Offset(const char* string);
+      Offset(const string& text);
       Offset(const size_t line, const size_t column);
 
       // return new position, incremented by the given string
       Offset inc(const char* begin, const char* end) const;
 
     public: // overload operators for position
+      void operator+= (const Offset &pos);
       bool operator== (const Offset &pos) const;
       bool operator!= (const Offset &pos) const;
-      const Offset operator+ (const Offset &off) const;
+      Offset operator+ (const Offset &off) const;
 
     public: // overload output stream operator
       // friend ostream& operator<<(ostream& strm, const Offset& off);
@@ -45,6 +48,7 @@ namespace Sass {
       Position(const size_t file, const size_t line, const size_t column);
 
     public: // overload operators for position
+      void operator+= (const Offset &off);
       bool operator== (const Position &pos) const;
       bool operator!= (const Position &pos) const;
       const Position operator+ (const Offset &off) const;

source_map.cpp

@@ -112,15 +112,51 @@ namespace Sass {
     return result;
   }
 
-  void SourceMap::update_column(const string& str)
+  void SourceMap::prepend(const OutputBuffer& out)
   {
-    const ptrdiff_t new_line_count = std::count(str.begin(), str.end(), '\n');
-    current_position.line += new_line_count;
-    if (new_line_count > 0) {
-      current_position.column = str.size() - str.find_last_of('\n') - 1;
-    } else {
-      current_position.column += str.size();
+    Offset size(out.smap.current_position);
+    for (Mapping mapping : out.smap.mappings) {
+      if (mapping.generated_position.line > size.line) {
+        throw(runtime_error("prepend sourcemap has illegal line"));
+      }
+      if (mapping.generated_position.line == size.line) {
+        if (mapping.generated_position.column > size.column) {
+          throw(runtime_error("prepend sourcemap has illegal column"));
+        }
+      }
+    }
+    // will adjust the offset
+    prepend(Offset(out.buffer));
+    // now add the new mappings
+    VECTOR_UNSHIFT(mappings, out.smap.mappings);
+  }
+
+  void SourceMap::append(const OutputBuffer& out)
+  {
+    append(Offset(out.buffer));
+  }
+
+  void SourceMap::prepend(const Offset& offset)
+  {
+    if (offset.line != 0 || offset.column != 0) {
+      for (Mapping& mapping : mappings) {
+        // move stuff on the first old line
+        if (mapping.generated_position.line == 0) {
+          mapping.generated_position.column += offset.column;
+        }
+        // make place for the new lines
+        mapping.generated_position.line += offset.line;
+      }
     }
+    if (current_position.line == 0) {
+      current_position.column += offset.column;
+    }
+    current_position.line += offset.line;
+  }
+
+  void SourceMap::append(const Offset& offset)
+  {
+    current_position += offset;
   }
 
   void SourceMap::add_open_mapping(AST_Node* node)

source_map.hpp

@@ -5,12 +5,17 @@
 
 #include "ast_fwd_decl.hpp"
 #include "base64vlq.hpp"
+#include "position.hpp"
 #include "mapping.hpp"
 
+#define VECTOR_PUSH(vec, ins) vec.insert(vec.end(), ins.begin(), ins.end())
+#define VECTOR_UNSHIFT(vec, ins) vec.insert(vec.begin(), ins.begin(), ins.end())
+
 namespace Sass {
   using std::vector;
 
   class Context;
+  class OutputBuffer;
 
   class SourceMap {
 
@@ -22,7 +27,10 @@ namespace Sass {
     void setFile(const string& str) {
       file = str;
     }
-    void update_column(const string& str);
+    void append(const Offset& offset);
+    void prepend(const Offset& offset);
+    void append(const OutputBuffer& out);
+    void prepend(const OutputBuffer& out);
     void add_open_mapping(AST_Node* node);
     void add_close_mapping(AST_Node* node);
 
@@ -41,6 +49,17 @@ namespace Sass {
     Base64VLQ base64vlq;
   };
 
+  class OutputBuffer {
+    public:
+      OutputBuffer(void)
+      : buffer(""),
+        smap()
+      { }
+    public:
+      string buffer;
+      SourceMap smap;
+  };
+
 }
 
 #endif