Ensure variationSan restores state stack and add regression test

src/ffishjs.cpp

@@ -211,17 +211,20 @@ class Board {
 
   std::string variation_san(std::string uciMoves, Notation notation, bool moveNumbers) {
     std::stringstream ss(uciMoves);
-    StateListPtr tempStates;
     std::vector<Move> moves;
     std::string variationSan = "";
     std::string uciMove;
     bool first = true;
+    bool invalidMoveEncountered = false;
+    size_t statesAdded = 0;
 
     while (std::getline(ss, uciMove, ' ')) {
       const Move move = UCI::to_move(this->pos, uciMove);
-      if (is_move_none<true>(move, uciMove, pos))
-        return "";
-      moves.emplace_back(UCI::to_move(this->pos, uciMove));
+      if (is_move_none<true>(move, uciMove, pos)) {
+        invalidMoveEncountered = true;
+        break;
+      }
+      moves.emplace_back(move);
       if (first) {
         first = false;
         if (moveNumbers) {
@@ -243,14 +246,22 @@ class Board {
         variationSan += SAN::move_to_san(this->pos, moves.back(), Notation(notation));
       }
       states->emplace_back();
+      ++statesAdded;
       pos.do_move(moves.back(), states->back());
     }
 
     // recover initial state
-    for(auto rIt = std::rbegin(moves); rIt != std::rend(moves); ++rIt) {
+    for (auto rIt = std::rbegin(moves); rIt != std::rend(moves); ++rIt)
       pos.undo_move(*rIt);
+
+    while (statesAdded > 0) {
+      states->pop_back();
+      --statesAdded;
     }
 
+    if (invalidMoveEncountered)
+      return "";
+
     return variationSan;
   }
 
@@ -271,6 +282,10 @@ class Board {
     return pos.game_ply();
   }
 
+  int state_stack_size() const {
+    return static_cast<int>(states->size());
+  }
+
   bool has_insufficient_material(bool turn) const {
     return Stockfish::has_insufficient_material(turn ? WHITE : BLACK, pos);
   }
@@ -712,6 +727,7 @@ EMSCRIPTEN_BINDINGS(ffish_js) {
     .function("fullmoveNumber", &Board::fullmove_number)
     .function("halfmoveClock", &Board::halfmove_clock)
     .function("gamePly", &Board::game_ply)
+    .function("stateStackSize", &Board::state_stack_size)
     .function("hasInsufficientMaterial", &Board::has_insufficient_material)
     .function("isInsufficientMaterial", &Board::is_insufficient_material)
     .function("isGameOver", select_overload<bool() const>(&Board::is_game_over))

tests/js/ffish.d.ts

@@ -55,6 +55,7 @@ export interface Board {
     fullmoveNumber(): number;
     halfmoveClock(): number;
     gamePly(): number;
+    stateStackSize(): number;
     hasInsufficientMaterial(turn: boolean): boolean;
     isInsufficientMaterial(): boolean;
     isGameOver(claimDraw?: boolean): boolean;

tests/js/test.js

@@ -282,6 +282,27 @@ describe('board.variationSan(uciMoves, notation, moveNumbers)', function () {
   });
 });
 
+describe('board.stateStackSize()', function () {
+  it("it remains aligned with the number of real moves after repeated variationSan calls", () => {
+    let board = new ffish.Board();
+    const actualMoves = ["e2e4", "e7e5", "g1f3"];
+    actualMoves.forEach(move => {
+      chai.expect(board.push(move)).to.equal(true);
+    });
+
+    const expectedStates = actualMoves.length + 1;
+    chai.expect(board.stateStackSize()).to.equal(expectedStates);
+
+    const variationLine = "g8f6 d2d3 Bf8c5";
+    for (let i = 0; i < 5; ++i) {
+      chai.expect(board.variationSan(variationLine)).to.not.equal("");
+      chai.expect(board.stateStackSize()).to.equal(expectedStates);
+    }
+
+    board.delete();
+  });
+});
+
 describe('board.turn()', function () {
   it("it returns the side to move", () => {
     let board = new ffish.Board();