Fix illegal extending when no blocks are found

Prints the exact error message as ruby sass.
Implements optional flag to suppress message.

ast.hpp

@@ -1704,6 +1704,8 @@ namespace Sass {
     ADD_PROPERTY(bool, has_line_feed);
     // line break after list separator
     ADD_PROPERTY(bool, has_line_break);
+    // maybe we have optional flag
+    ADD_PROPERTY(bool, is_optional);
     // parent media block (for extend check)
     ADD_PROPERTY(Media_Block*, media_block);
   public:
@@ -1713,6 +1715,7 @@ namespace Sass {
       has_placeholder_(h),
       has_line_feed_(false),
       has_line_break_(false),
+      is_optional_(false),
       media_block_(0)
     { }
     virtual ~Selector() = 0;

debugger.hpp

@@ -40,6 +40,7 @@ inline void debug_ast(AST_Node* node, string ind = "", Env* env = 0)
 
     cerr << ind << "Selector_List " << selector
       << " [mq:" << selector->media_block() << "]"
+      << (selector->is_optional() ? " [is_optional]": " -")
       << (selector->has_line_break() ? " [line-break]": " -")
       << (selector->has_line_feed() ? " [line-feed]": " -")
     << endl;
@@ -54,6 +55,7 @@ inline void debug_ast(AST_Node* node, string ind = "", Env* env = 0)
     Complex_Selector* selector = dynamic_cast<Complex_Selector*>(node);
     cerr << ind << "Complex_Selector " << selector
       << " [mq:" << selector->media_block() << "]"
+      << (selector->is_optional() ? " [is_optional]": " -")
       << (selector->has_line_break() ? " [line-break]": " -")
       << (selector->has_line_feed() ? " [line-feed]": " -") << " -> ";
       switch (selector->combinator()) {
@@ -69,6 +71,7 @@ inline void debug_ast(AST_Node* node, string ind = "", Env* env = 0)
     Compound_Selector* selector = dynamic_cast<Compound_Selector*>(node);
     cerr << ind << "Compound_Selector " << selector
       << " [mq:" << selector->media_block() << "]"
+      << (selector->is_optional() ? " [is_optional]": " -")
       << (selector->has_line_break() ? " [line-break]": " -")
       << (selector->has_line_feed() ? " [line-feed]": " -") <<
       " <" << prettyprint(selector->pstate().token.ws_before()) << "> X <" << prettyprint(selector->pstate().token.ws_after()) << ">" << endl;
@@ -101,6 +104,7 @@ inline void debug_ast(AST_Node* node, string ind = "", Env* env = 0)
     Selector_Placeholder* selector = dynamic_cast<Selector_Placeholder*>(node);
     cerr << ind << "Selector_Placeholder [" << selector->name() << "] " << selector
       << " [mq:" << selector->media_block() << "]"
+      << (selector->is_optional() ? " [is_optional]": " -")
       << (selector->has_line_break() ? " [line-break]": " -")
       << (selector->has_line_feed() ? " [line-feed]": " -")
     << endl;

expand.cpp

@@ -404,7 +404,8 @@ namespace Sass {
     To_String to_string(&ctx);
     Selector_List* extender = static_cast<Selector_List*>(selector_stack.back());
     if (!extender) return 0;
-    Selector_List* extendee = static_cast<Selector_List*>(e->selector()->perform(contextualize->with(0, env, backtrace)));
+    Selector_List* org_extendee = static_cast<Selector_List*>(e->selector());
+    Selector_List* extendee = static_cast<Selector_List*>(org_extendee->perform(contextualize->with(0, env, backtrace)));
     if (extendee->length() != 1) {
       error("selector groups may not be extended", extendee->pstate(), backtrace);
     }
@@ -413,7 +414,7 @@ namespace Sass {
       error("nested selectors may not be extended", c->pstate(), backtrace);
     }
     Compound_Selector* s = c->head();
-
+    s->is_optional(org_extendee->is_optional());
     // // need to convert the compound selector into a by-value data structure
     // vector<string> target_vec;
     // for (size_t i = 0, L = s->length(); i < L; ++i)

extend.cpp

@@ -5,6 +5,7 @@
 #include "backtrace.hpp"
 #include "paths.hpp"
 #include "parser.hpp"
+#include "debugger.hpp"
 #include "node.hpp"
 #include "sass_util.hpp"
 #include "debug.hpp"
@@ -1678,10 +1679,10 @@ namespace Sass {
         for (ExtensionPair ext : entries) {
           // check if both selectors have the same media block parent
           if (ext.first->media_block() == pComplexSelector->media_block()) continue;
+          // fail if one goes across media block boundaries
           stringstream err;
           To_String to_string(&ctx);
           string cwd(Sass::File::get_cwd());
-          // make path relative to the current directory
           ParserState pstate(ext.second->pstate());
           string rel_path(Sass::File::resolve_relative_path(pstate.path, cwd, cwd));
           err << "You may not @extend an outer selector from within @media.\n";
@@ -1690,12 +1691,33 @@ namespace Sass {
           err << " on line " << pstate.line+1 << " of " << rel_path << "\n";
           error(err.str(), pComplexSelector->pstate());
         }
-        hasExtension = entries.size() > 0;
+        if (entries.size() > 0) hasExtension = true;
       }
 
       pIter = pIter->tail();
     }
 
+    if (!hasExtension) {
+      stringstream err;
+      To_String to_string(&ctx);
+      string cwd(Sass::File::get_cwd());
+      string sel1(pComplexSelector->perform(&to_string));
+      Compound_Selector* pExtendSelector = 0;
+      for (auto i : subsetMap.values()) {
+        if (i.first == pComplexSelector) {
+          pExtendSelector = i.second;
+          break;
+        }
+      }
+      if (!pExtendSelector->is_optional()) {
+        string sel2(pExtendSelector ? pExtendSelector->perform(&to_string) : "[unknown]");
+        err << "\"" << sel1 << "\" failed to @extend \"" << sel2 << "\"\n";
+        err << "The selector \"" << sel2 << "\" was not found.\n";
+        err << "Use \"@extend " << sel2 << " !optional\" if the extend should be able to fail.";
+        error(err.str(), pExtendSelector ? pExtendSelector->pstate() : pComplexSelector->pstate());
+      }
+    }
+
     return hasExtension;
   }
 

parser.cpp

@@ -497,7 +497,9 @@ namespace Sass {
       (*group) << comb;
     }
     while (reloop);
-    while (lex< optional >());    // JMA - ignore optional flag if it follows the selector group
+    while (lex< optional >()) {
+      group->is_optional(true);
+    }
     return group;
   }
 

subset_map.hpp

@@ -82,6 +82,7 @@ namespace Sass {
     vector<V> get_v(const vector<K>& s);
     bool empty() { return values_.empty(); }
     void clear() { values_.clear(); hash_.clear(); }
+    const vector<V> values(void) { return values_; }
   };
 
   template<typename K, typename V>