Add basic concept support (#144)

test/CMakeLists.txt

@@ -14,6 +14,7 @@ set(tests
         cpp_attribute.cpp
         cpp_class.cpp
         cpp_class_template.cpp
+        cpp_concept.cpp
         cpp_enum.cpp
         cpp_friend.cpp
         cpp_function.cpp

test/cpp_concept.cpp

@@ -0,0 +1,85 @@
+// Copyright (C) 2017-2022 Jonathan Müller and cppast contributors
+// SPDX-License-Identifier: MIT
+
+#include <cppast/cpp_concept.hpp>
+
+#include <cppast/cpp_function_template.hpp>
+
+#include "test_parser.hpp"
+
+using namespace cppast;
+
+TEST_CASE("cpp_concept") 
+{
+    if (libclang_parser::libclang_minor_version() < 60)
+        return;
+
+    auto code = R"(
+#include <concepts>
+
+/// template<typename T>
+/// concept a = requires(T t, int i)
+/// {
+///   {t.a()};
+///   {t.b()} -> std::copy_constructible;
+///   {t.c(i)} -> std::same_as<int>;
+///   typename T::inner;
+/// };
+template<typename T>
+concept a = requires(T t, int i)
+{
+    {t.a()};
+    {t.b()} -> std::copy_constructible;
+    {t.c(i)} -> std::same_as<int>;
+    typename T::inner;
+};
+
+/// template<typename T>
+/// concept b = a<T> && std::constructible_from<T, int>;
+template<typename T>
+concept b = a<T> && std::constructible_from<T, int>;
+
+/// template<typename T>
+/// void f1(T param);
+template<typename T>
+    requires a<T>
+void f1(T param);
+
+/// template<b T>
+/// void f2(T param);
+template<b T>
+void f2(T param);
+
+/// template<std::convertible_to<int> T>
+/// void f3(T param);
+template<std::convertible_to<int> T>
+void f3(T param);
+
+)";
+    cpp_entity_index idx;
+    auto             file = parse(idx, "cpp_concept.cpp", code, false, cppast::cpp_standard::cpp_20);
+
+    auto count = test_visit<cpp_concept>(*file, [&](const cpp_concept& con) {}, false);
+    REQUIRE(count == 2u);
+
+    count = test_visit<cpp_function_template>(*file, [&](const cpp_function_template& tfunc) {
+        REQUIRE(is_templated(tfunc.function()));
+        REQUIRE(!tfunc.scope_name());
+        check_template_parameters(tfunc, {{cpp_entity_kind::template_type_parameter_t, "T"}});
+
+        if(tfunc.name() == "f1")
+        {
+            REQUIRE(
+                static_cast<const cpp_template_type_parameter&>(*tfunc.parameters().begin()).keyword()
+                == cpp_template_keyword::keyword_typename);
+        }
+        else if (tfunc.name() == "f2" || tfunc.name() == "f3")
+        {
+            REQUIRE(static_cast<const cpp_template_type_parameter&>(*tfunc.parameters().begin())
+                        .keyword()
+                    == cpp_template_keyword::concept_contraint);
+        }
+    });
+
+    REQUIRE(count == 3u);
+}