Add basic scripting support.

- Fix certain bugs in ruby parser
- And a lot more cleanup/minor fixes.

include/internal/syntax/decl.h

@@ -48,6 +48,7 @@ struct ParseState {
     uint64_t line, uint64_t original, uint64_t final
   );
   static ParseState *concat(Language &lang, ParseState *a, ParseState *b);
+  static void *state_before(Language &lang, ParseState *root, vase::Shard *vase, uint64_t line);
 };
 
 struct ParseStateBranch : ParseState {
@@ -83,18 +84,25 @@ struct ParsePieceBuilder {
   std::vector<ParseState *> pieces;
   std::vector<uint16_t> blocks;
   void *piece_state{nullptr};
+  void *prev_state{nullptr};
   uint64_t chunk_start{0};
   uint64_t chunk_lines{0};
-  ParsePieceBuilder(Language &lang, uint64_t first_line)
-      : lang(lang), chunk_start(first_line) {}
-  void add(
-    void *state,
-    uint64_t line,
-    const std::vector<ParseEvent> &events
-  ) {
+  ParsePieceBuilder(Language &lang, uint64_t first_line, void *entry_state)
+      : lang(lang), chunk_start(first_line) {
+    prev_state = lang.copy(entry_state);
+  }
+  ~ParsePieceBuilder() {
+    if (prev_state)
+      lang.destroy(prev_state);
+    if (piece_state)
+      lang.destroy(piece_state);
+  }
+  ParsePieceBuilder(const ParsePieceBuilder &) = delete;
+  ParsePieceBuilder &operator=(const ParsePieceBuilder &) = delete;
+  void add(void *state, uint64_t line, const std::vector<ParseEvent> &events) {
     if (chunk_lines == 0) {
       chunk_start = line;
-      piece_state = lang.copy(state);
+      piece_state = lang.copy(prev_state);
     }
     for (const auto &ev : events) {
       blocks.push_back(
@@ -103,6 +111,9 @@ struct ParsePieceBuilder {
       );
     }
     ++chunk_lines;
+    if (prev_state)
+      lang.destroy(prev_state);
+    prev_state = lang.copy(state);
     if (chunk_lines == ParseStateLeaf::MAX_CHUNK)
       flush();
   }

include/internal/syntax/parser.h

@@ -13,6 +13,7 @@ ParserSnapshot make_parser(vase::Shard *vase, uint64_t lines, Language *lang);
 ParserSnapshot retain(const ParserSnapshot &snap);
 void release(ParserSnapshot &snap);
 
+void *state_before(const ParserSnapshot &snap, vase::Shard *vase, uint64_t line);
 uint64_t next_closing(const ParserSnapshot &snap, uint64_t line);
 uint64_t prev_opening(const ParserSnapshot &snap, uint64_t line);