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/tune.cpp

@@ -34,75 +34,84 @@ using std::string;
 
 namespace Stockfish {
 
-bool Tune::update_on_last;
-const UCI::Option* LastOption = nullptr;
+bool                              Tune::update_on_last;
+const UCI::Option*                LastOption = nullptr;
 static std::map<std::string, int> TuneResults;
 
 string Tune::next(string& names, bool pop) {
 
-  string name;
+    string name;
 
-  do {
-      string token = names.substr(0, names.find(','));
+    do
+    {
+        string token = names.substr(0, names.find(','));
 
-      if (pop)
-          names.erase(0, token.size() + 1);
+        if (pop)
+            names.erase(0, token.size() + 1);
 
-      std::stringstream ws(token);
-      name += (ws >> token, token); // Remove trailing whitespace
+        std::stringstream ws(token);
+        name += (ws >> token, token);  // Remove trailing whitespace
 
-  } while (  std::count(name.begin(), name.end(), '(')
-           - std::count(name.begin(), name.end(), ')'));
+    } while (std::count(name.begin(), name.end(), '(') - std::count(name.begin(), name.end(), ')'));
 
-  return name;
+    return name;
 }
 
 static void on_tune(const UCI::Option& o) {
 
-  if (!Tune::update_on_last || LastOption == &o)
-      Tune::read_options();
+    if (!Tune::update_on_last || LastOption == &o)
+        Tune::read_options();
 }
 
 static void make_option(const string& n, int v, const SetRange& r) {
 
-  // Do not generate option when there is nothing to tune (ie. min = max)
-  if (r(v).first == r(v).second)
-      return;
+    // Do not generate option when there is nothing to tune (ie. min = max)
+    if (r(v).first == r(v).second)
+        return;
 
-  if (TuneResults.count(n))
-      v = TuneResults[n];
+    if (TuneResults.count(n))
+        v = TuneResults[n];
 
-  Options[n] << UCI::Option(v, r(v).first, r(v).second, on_tune);
-  LastOption = &Options[n];
+    Options[n] << UCI::Option(v, r(v).first, r(v).second, on_tune);
+    LastOption = &Options[n];
 
-  // Print formatted parameters, ready to be copy-pasted in Fishtest
-  std::cout << n << ","
-            << v << ","
-            << r(v).first << "," << r(v).second << ","
-            << (r(v).second - r(v).first) / 20.0 << ","
-            << "0.0020"
-            << std::endl;
+    // Print formatted parameters, ready to be copy-pasted in Fishtest
+    std::cout << n << "," << v << "," << r(v).first << "," << r(v).second << ","
+              << (r(v).second - r(v).first) / 20.0 << ","
+              << "0.0020" << std::endl;
 }
 
-template<> void Tune::Entry<int>::init_option() { make_option(name, value, range); }
-
-template<> void Tune::Entry<int>::read_option() {
-  if (Options.count(name))
-      value = int(Options[name]);
+template<>
+void Tune::Entry<int>::init_option() {
+    make_option(name, value, range);
 }
 
-template<> void Tune::Entry<Value>::init_option() { make_option(name, value, range); }
+template<>
+void Tune::Entry<int>::read_option() {
+    if (Options.count(name))
+        value = int(Options[name]);
+}
 
-template<> void Tune::Entry<Value>::read_option() {
-  if (Options.count(name))
-      value = Value(int(Options[name]));
+template<>
+void Tune::Entry<Value>::init_option() {
+    make_option(name, value, range);
+}
+
+template<>
+void Tune::Entry<Value>::read_option() {
+    if (Options.count(name))
+        value = Value(int(Options[name]));
 }
 
 // Instead of a variable here we have a PostUpdate function: just call it
-template<> void Tune::Entry<Tune::PostUpdate>::init_option() {}
-template<> void Tune::Entry<Tune::PostUpdate>::read_option() { value(); }
+template<>
+void Tune::Entry<Tune::PostUpdate>::init_option() {}
+template<>
+void Tune::Entry<Tune::PostUpdate>::read_option() {
+    value();
+}
 
-} // namespace Stockfish
+}  // namespace Stockfish
 
 
 // Init options with tuning session results instead of default values. Useful to
@@ -117,9 +126,7 @@ template<> void Tune::Entry<Tune::PostUpdate>::read_option() { value(); }
 
 namespace Stockfish {
 
-void Tune::read_results() {
-
-  /* ...insert your values here... */
+void Tune::read_results() { /* ...insert your values here... */
 }
 
-} // namespace Stockfish
+}  // namespace Stockfish