add clang-format

This introduces clang-format to enforce a consistent code style for Stockfish.

Having a documented and consistent style across the code will make contributing easier
for new developers, and will make larger changes to the codebase easier to make.

To facilitate formatting, this PR includes a Makefile target (`make format`) to format the code,
this requires clang-format (version 17 currently) to be installed locally.

Installing clang-format is straightforward on most OS and distros
(e.g. with https://apt.llvm.org/, brew install clang-format, etc), as this is part of quite commonly
used suite of tools and compilers (llvm / clang).

Additionally, a CI action is present that will verify if the code requires formatting,
and comment on the PR as needed. Initially, correct formatting is not required, it will be
done by maintainers as part of the merge or in later commits, but obviously this is encouraged.

fixes https://github.com/official-stockfish/Stockfish/issues/3608
closes https://github.com/official-stockfish/Stockfish/pull/4790

Co-Authored-By: Joost VandeVondele <Joost.VandeVondele@gmail.com>

src/movepick.h

@@ -24,7 +24,7 @@
 #include <cstdint>
 #include <cstdlib>
 #include <limits>
-#include <type_traits> // IWYU pragma: keep
+#include <type_traits>  // IWYU pragma: keep
 
 #include "movegen.h"
 #include "types.h"
@@ -39,22 +39,22 @@ class Position;
 template<typename T, int D>
 class StatsEntry {
 
-  T entry;
+    T entry;
 
-public:
-  void operator=(const T& v) { entry = v; }
-  T* operator&() { return &entry; }
-  T* operator->() { return &entry; }
-  operator const T&() const { return entry; }
+   public:
+    void operator=(const T& v) { entry = v; }
+    T*   operator&() { return &entry; }
+    T*   operator->() { return &entry; }
+    operator const T&() const { return entry; }
 
-  void operator<<(int bonus) {
-    assert(abs(bonus) <= D); // Ensure range is [-D, D]
-    static_assert(D <= std::numeric_limits<T>::max(), "D overflows T");
+    void operator<<(int bonus) {
+        assert(abs(bonus) <= D);  // Ensure range is [-D, D]
+        static_assert(D <= std::numeric_limits<T>::max(), "D overflows T");
 
-    entry += (bonus * D - entry * abs(bonus)) / (D * 5 / 4);
+        entry += (bonus * D - entry * abs(bonus)) / (D * 5 / 4);
 
-    assert(abs(entry) <= D);
-  }
+        assert(abs(entry) <= D);
+    }
 };
 
 // Stats is a generic N-dimensional array used to store various statistics.
@@ -62,28 +62,32 @@ public:
 // template parameter D limits the range of updates in [-D, D] when we update
 // values with the << operator, while the last parameters (Size and Sizes)
 // encode the dimensions of the array.
-template <typename T, int D, int Size, int... Sizes>
-struct Stats : public std::array<Stats<T, D, Sizes...>, Size>
-{
-  using stats = Stats<T, D, Size, Sizes...>;
+template<typename T, int D, int Size, int... Sizes>
+struct Stats: public std::array<Stats<T, D, Sizes...>, Size> {
+    using stats = Stats<T, D, Size, Sizes...>;
 
-  void fill(const T& v) {
+    void fill(const T& v) {
 
-    // For standard-layout 'this' points to the first struct member
-    assert(std::is_standard_layout_v<stats>);
+        // For standard-layout 'this' points to the first struct member
+        assert(std::is_standard_layout_v<stats>);
 
-    using entry = StatsEntry<T, D>;
-    entry* p = reinterpret_cast<entry*>(this);
-    std::fill(p, p + sizeof(*this) / sizeof(entry), v);
-  }
+        using entry = StatsEntry<T, D>;
+        entry* p    = reinterpret_cast<entry*>(this);
+        std::fill(p, p + sizeof(*this) / sizeof(entry), v);
+    }
 };
 
-template <typename T, int D, int Size>
-struct Stats<T, D, Size> : public std::array<StatsEntry<T, D>, Size> {};
+template<typename T, int D, int Size>
+struct Stats<T, D, Size>: public std::array<StatsEntry<T, D>, Size> {};
 
 // In stats table, D=0 means that the template parameter is not used
-enum StatsParams { NOT_USED = 0 };
-enum StatsType { NoCaptures, Captures };
+enum StatsParams {
+    NOT_USED = 0
+};
+enum StatsType {
+    NoCaptures,
+    Captures
+};
 
 // ButterflyHistory records how often quiet moves have been successful or
 // unsuccessful during the current search, and is used for reduction and move
@@ -117,42 +121,53 @@ using ContinuationHistory = Stats<PieceToHistory, NOT_USED, PIECE_NB, SQUARE_NB>
 // likely to get a cut-off first.
 class MovePicker {
 
-  enum PickType { Next, Best };
+    enum PickType {
+        Next,
+        Best
+    };
 
-public:
-  MovePicker(const MovePicker&) = delete;
-  MovePicker& operator=(const MovePicker&) = delete;
-  MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
-                                           const CapturePieceToHistory*,
-                                           const PieceToHistory**,
-                                           Move,
-                                           const Move*);
-  MovePicker(const Position&, Move, Depth, const ButterflyHistory*,
-                                           const CapturePieceToHistory*,
-                                           const PieceToHistory**,
-                                           Square);
-  MovePicker(const Position&, Move, Value, const CapturePieceToHistory*);
-  Move next_move(bool skipQuiets = false);
+   public:
+    MovePicker(const MovePicker&)            = delete;
+    MovePicker& operator=(const MovePicker&) = delete;
+    MovePicker(const Position&,
+               Move,
+               Depth,
+               const ButterflyHistory*,
+               const CapturePieceToHistory*,
+               const PieceToHistory**,
+               Move,
+               const Move*);
+    MovePicker(const Position&,
+               Move,
+               Depth,
+               const ButterflyHistory*,
+               const CapturePieceToHistory*,
+               const PieceToHistory**,
+               Square);
+    MovePicker(const Position&, Move, Value, const CapturePieceToHistory*);
+    Move next_move(bool skipQuiets = false);
 
-private:
-  template<PickType T, typename Pred> Move select(Pred);
-  template<GenType> void score();
-  ExtMove* begin() { return cur; }
-  ExtMove* end() { return endMoves; }
+   private:
+    template<PickType T, typename Pred>
+    Move select(Pred);
+    template<GenType>
+    void     score();
+    ExtMove* begin() { return cur; }
+    ExtMove* end() { return endMoves; }
 
-  const Position& pos;
-  const ButterflyHistory* mainHistory;
-  const CapturePieceToHistory* captureHistory;
-  const PieceToHistory** continuationHistory;
-  Move ttMove;
-  ExtMove refutations[3], *cur, *endMoves, *endBadCaptures;
-  int stage;
-  Square recaptureSquare;
-  Value threshold;
-  Depth depth;
-  ExtMove moves[MAX_MOVES];
+    const Position&              pos;
+    const ButterflyHistory*      mainHistory;
+    const CapturePieceToHistory* captureHistory;
+    const PieceToHistory**       continuationHistory;
+    Move                         ttMove;
+    ExtMove                      refutations[3], *cur, *endMoves, *endBadCaptures;
+    int                          stage;
+    Square                       recaptureSquare;
+    Value                        threshold;
+    Depth                        depth;
+    ExtMove                      moves[MAX_MOVES];
 };
 
-} // namespace Stockfish
+}  // namespace Stockfish
 
-#endif // #ifndef MOVEPICK_H_INCLUDED
+#endif  // #ifndef MOVEPICK_H_INCLUDED