fix: missing function definition (#793)

* the get_option_group definition was missing from the splitting of the calls.

* style: pre-commit.ci fixes

* the get_option_group definition was missing from the splitting of the calls.

* style: pre-commit.ci fixes

* add test for missing function

* style: pre-commit.ci fixes

* add test for get_option_group

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: phlptp

include/CLI/impl/App_inl.hpp

@@ -433,6 +433,15 @@ CLI11_NODISCARD CLI11_INLINE CLI::App_p App::get_subcommand_ptr(int index) const
     throw OptionNotFound(std::to_string(index));
 }
 
+CLI11_NODISCARD CLI11_INLINE CLI::App *App::get_option_group(std::string group_name) const {
+    for(const App_p &app : subcommands_) {
+        if(app->name_.empty() && app->group_ == group_name) {
+            return app.get();
+        }
+    }
+    throw OptionNotFound(group_name);
+}
+
 CLI11_NODISCARD CLI11_INLINE std::size_t App::count_all() const {
     std::size_t cnt{0};
     for(const auto &opt : options_) {

tests/OptionGroupTest.cpp

@@ -448,6 +448,12 @@ TEST_CASE_METHOD(ManyGroups, "SingleGroup", "[optiongroup]") {
     CHECK_THROWS_AS(run(), CLI::RequiredError);
 }
 
+TEST_CASE_METHOD(ManyGroups, "getGroup", "[optiongroup]") {
+    auto *mn = app.get_option_group("main");
+    CHECK(mn == main);
+    CHECK_THROWS_AS(app.get_option_group("notfound"), CLI::OptionNotFound);
+}
+
 TEST_CASE_METHOD(ManyGroups, "ExcludesGroup", "[optiongroup]") {
     // only 1 group can be used
     g1->excludes(g2);