Add basic concept support (#144)

include/cppast/cpp_concept.hpp

@@ -0,0 +1,74 @@
+// Copyright (C) 2017-2022 Jonathan Müller and cppast contributors
+// SPDX-License-Identifier: MIT
+
+#ifndef CPPAST_CPP_CONCEPT_HPP_INCLUDED
+#define CPPAST_CPP_CONCEPT_HPP_INCLUDED
+
+#include <cppast/cpp_entity.hpp>
+#include <cppast/cpp_template_parameter.hpp>
+#include <cppast/cpp_expression.hpp>
+
+namespace cppast
+{
+/// A [[cppast::cpp_entity]() modelling a c++ concept declaration
+/// \notes while concepts are technically templates,
+/// this is not a [cppast::cpp_template](),
+/// as concepts act very differently from other templates
+class cpp_concept final : public cpp_entity
+{
+public:
+    static cpp_entity_kind kind() noexcept;
+
+    /// \returns the template parameters as a string
+    const cpp_token_string& parameters() const noexcept
+    {
+        return parameters_;
+    }
+
+    /// \returns the [cppast::cpp_expression]() defining the concept constraint
+    const cpp_expression& constraint_expression() const noexcept
+    {
+        return *expression_;
+    }
+
+    class builder
+    {
+    public:
+        builder(std::string name)
+        : concept_(new cpp_concept(std::move(name)))
+        {}
+
+        cpp_token_string& set_parameters(cpp_token_string string) noexcept
+        {
+            concept_->parameters_ = std::move(string);
+            return concept_->parameters_;
+        }
+
+        cpp_expression& set_expression(std::unique_ptr<cpp_expression> expression) noexcept
+        {
+            concept_->expression_ = std::move(expression);
+            return *concept_->expression_;
+        }
+
+        std::unique_ptr<cpp_concept> finish(const cpp_entity_index& idx, cpp_entity_id id);
+
+    private:
+        std::unique_ptr<cpp_concept> concept_;
+    };
+
+private:
+    cpp_concept(std::string name) 
+        : cpp_entity(std::move(name)), parameters_({})
+    {}
+
+    cpp_entity_kind do_get_entity_kind() const noexcept override;
+
+    cpp_token_string parameters_;
+
+    std::unique_ptr<cpp_expression> expression_;
+};
+
+
+} // namespace cppast
+
+#endif

include/cppast/cpp_entity_kind.hpp

@@ -57,6 +57,7 @@ enum class cpp_entity_kind
     function_template_specialization_t,
     class_template_t,
     class_template_specialization_t,
+    concept_t,
 
     static_assert_t,
 

include/cppast/cpp_template.hpp

@@ -15,7 +15,7 @@
 
 namespace cppast
 {
-/// Base class for all entities modelling a C++ template of some kind.
+/// Base class for all entities modelling a C++ template of some kind, aside from concepts
 ///
 /// It is a container of a single [cppast::cpp_entity]() that is the entity being templated.
 class cpp_template : public cpp_entity, public cpp_entity_container<cpp_template, cpp_entity>

include/cppast/cpp_template_parameter.hpp

@@ -36,7 +36,8 @@ private:
 enum class cpp_template_keyword
 {
     keyword_class,
-    keyword_typename
+    keyword_typename,
+    concept_contraint
 };
 
 /// \returns The string associated of the keyword.
@@ -52,7 +53,8 @@ public:
     /// \notes The `default_type` may be `nullptr` in which case the parameter has no default.
     static std::unique_ptr<cpp_template_type_parameter> build(
         const cpp_entity_index& idx, cpp_entity_id id, std::string name, cpp_template_keyword kw,
-        bool variadic, std::unique_ptr<cpp_type> default_type = nullptr);
+        bool variadic, std::unique_ptr<cpp_type> default_type = nullptr,
+        type_safe::optional<cpp_token_string> concept_constraint = type_safe::nullopt);
 
     /// \returns A [ts::optional_ref]() to the default type.
     type_safe::optional_ref<const cpp_type> default_type() const noexcept
@@ -66,17 +68,24 @@ public:
         return keyword_;
     }
 
+    const type_safe::optional<cpp_token_string>& concept_constraint() const noexcept
+    {
+        return concept_constraint_;
+    }
+
 private:
     cpp_template_type_parameter(std::string name, cpp_template_keyword kw, bool variadic,
-                                std::unique_ptr<cpp_type> default_type)
+                                std::unique_ptr<cpp_type>             default_type,
+                                type_safe::optional<cpp_token_string> concept_constraint)
     : cpp_template_parameter(std::move(name), variadic), default_type_(std::move(default_type)),
-      keyword_(kw)
+      keyword_(kw), concept_constraint_(concept_constraint)
     {}
 
     cpp_entity_kind do_get_entity_kind() const noexcept override;
 
     std::unique_ptr<cpp_type> default_type_;
     cpp_template_keyword      keyword_;
+    type_safe::optional<cpp_token_string> concept_constraint_;
 };
 
 /// \exclude

include/cppast/cppast_fwd.hpp

@@ -20,6 +20,7 @@ class cpp_builtin_type;
 class cpp_class;
 class cpp_class_template;
 class cpp_class_template_specialization;
+class cpp_concept;
 class cpp_constructor;
 class cpp_conversion_op;
 class cpp_cv_qualified_type;

src/CMakeLists.txt

@@ -13,6 +13,7 @@ set(header
     ../include/cppast/cpp_attribute.hpp
     ../include/cppast/cpp_class.hpp
     ../include/cppast/cpp_class_template.hpp
+    ../include/cppast/cpp_concept.hpp
     ../include/cppast/cpp_decltype_type.hpp
     ../include/cppast/cpp_entity.hpp
     ../include/cppast/cpp_entity_container.hpp
@@ -54,6 +55,7 @@ set(source
         cpp_attribute.cpp
         cpp_class.cpp
         cpp_class_template.cpp
+        cpp_concept.cpp
         cpp_entity.cpp
         cpp_entity_index.cpp
         cpp_entity_kind.cpp
@@ -80,6 +82,7 @@ set(source
         visitor.cpp)
 set(libclang_source
         libclang/class_parser.cpp
+        libclang/concept_parser.cpp
         libclang/cxtokenizer.cpp
         libclang/cxtokenizer.hpp
         libclang/debug_helper.cpp

src/code_generator.cpp

@@ -6,6 +6,7 @@
 #include <cppast/cpp_alias_template.hpp>
 #include <cppast/cpp_class.hpp>
 #include <cppast/cpp_class_template.hpp>
+#include <cppast/cpp_concept.hpp>
 #include <cppast/cpp_entity_kind.hpp>
 #include <cppast/cpp_enum.hpp>
 #include <cppast/cpp_file.hpp>
@@ -879,6 +880,9 @@ bool generate_template_type_parameter(code_generator&                    generat
     code_generator::output output(type_safe::ref(generator), type_safe::ref(param), cur_access);
     if (output)
     {
+        if(param.keyword() == cpp_template_keyword::concept_contraint)
+            detail::write_token_string(output, param.concept_constraint().value());
+        else
             output << keyword(to_string(param.keyword()));
         if (param.is_variadic())
             output << operator_ws << punctuation("...");
@@ -1036,6 +1040,23 @@ bool generate_class_template_specialization(code_generator&
     return static_cast<bool>(output);
 }
 
+bool generate_concept(code_generator&           generator,
+                      const cpp_concept&        con,
+                      cpp_access_specifier_kind cur_access)
+{
+    code_generator::output output(type_safe::ref(generator), type_safe::ref(con), cur_access);
+    if(output)
+    {
+        output << keyword("template") << operator_ws << punctuation("<") << bracket_ws;
+        detail::write_token_string(output, con.parameters());
+        output << bracket_ws << punctuation(">") << newl;
+        output << keyword("concept") << operator_ws << identifier(con.name()) << operator_ws << punctuation("=") << operator_ws;
+        detail::write_expression(output, con.constraint_expression());
+        output << operator_ws << punctuation(";") << newl; 
+    }
+    return static_cast<bool>(output);
+}
+
 bool generate_static_assert(code_generator& generator, const cpp_static_assert& assert,
                             cpp_access_specifier_kind cur_access)
 {
@@ -1115,6 +1136,7 @@ bool generate_code_impl(code_generator& generator, const cpp_entity& e,
         CPPAST_DETAIL_HANDLE(function_template_specialization)
         CPPAST_DETAIL_HANDLE(class_template)
         CPPAST_DETAIL_HANDLE(class_template_specialization)
+        CPPAST_DETAIL_HANDLE(concept)
 
         CPPAST_DETAIL_HANDLE(static_assert)
 

src/cpp_concept.cpp

@@ -0,0 +1,24 @@
+// Copyright (C) 2017-2022 Jonathan Müller and cppast contributors
+// SPDX-License-Identifier: MIT
+
+#include <cppast/cpp_concept.hpp>
+
+#include <cppast/cpp_entity_kind.hpp>
+
+using namespace cppast;
+
+cpp_entity_kind cppast::cpp_concept::kind() noexcept
+{
+    return cpp_entity_kind::concept_t;
+}
+
+cpp_entity_kind cpp_concept::do_get_entity_kind() const noexcept
+{
+    return cpp_entity_kind::concept_t;
+}
+
+std::unique_ptr<cpp_concept> cpp_concept::builder::finish(const cpp_entity_index& idx, cpp_entity_id id)
+{
+    idx.register_definition(id, type_safe::ref(*concept_));
+    return std::move(concept_);
+}

src/cpp_entity_kind.cpp

@@ -88,6 +88,8 @@ const char* cppast::to_string(cpp_entity_kind kind) noexcept
         return "class template";
     case cpp_entity_kind::class_template_specialization_t:
         return "class template specialization";
+    case cpp_entity_kind::concept_t:
+        return "concept";
 
     case cpp_entity_kind::static_assert_t:
         return "static_assert";
@@ -142,6 +144,7 @@ bool cppast::is_function(cpp_entity_kind kind) noexcept
     case cpp_entity_kind::function_template_specialization_t:
     case cpp_entity_kind::class_template_t:
     case cpp_entity_kind::class_template_specialization_t:
+    case cpp_entity_kind::concept_t:
     case cpp_entity_kind::static_assert_t:
     case cpp_entity_kind::unexposed_t:
     case cpp_entity_kind::count:
@@ -191,6 +194,7 @@ bool cppast::is_parameter(cpp_entity_kind kind) noexcept
     case cpp_entity_kind::function_template_specialization_t:
     case cpp_entity_kind::class_template_t:
     case cpp_entity_kind::class_template_specialization_t:
+    case cpp_entity_kind::concept_t:
     case cpp_entity_kind::static_assert_t:
     case cpp_entity_kind::unexposed_t:
     case cpp_entity_kind::count:
@@ -209,6 +213,7 @@ bool cppast::is_template(cpp_entity_kind kind) noexcept
     case cpp_entity_kind::function_template_specialization_t:
     case cpp_entity_kind::class_template_t:
     case cpp_entity_kind::class_template_specialization_t:
+    case cpp_entity_kind::concept_t:
         return true;
 
     case cpp_entity_kind::file_t:
@@ -288,6 +293,7 @@ bool cppast::is_template_specialization(cpp_entity_kind kind) noexcept
     case cpp_entity_kind::variable_template_t:
     case cpp_entity_kind::function_template_t:
     case cpp_entity_kind::class_template_t:
+    case cpp_entity_kind::concept_t:
     case cpp_entity_kind::static_assert_t:
     case cpp_entity_kind::unexposed_t:
     case cpp_entity_kind::count:

src/cpp_forward_declarable.cpp

@@ -56,6 +56,7 @@ type_safe::optional_ref<const cpp_forward_declarable> get_declarable(const cpp_e
     case cpp_entity_kind::template_type_parameter_t:
     case cpp_entity_kind::non_type_template_parameter_t:
     case cpp_entity_kind::template_template_parameter_t:
+    case cpp_entity_kind::concept_t:
     case cpp_entity_kind::alias_template_t:
     case cpp_entity_kind::variable_template_t:
     case cpp_entity_kind::static_assert_t:

src/cpp_template_parameter.cpp

@@ -15,6 +15,8 @@ const char* cppast::to_string(cpp_template_keyword kw) noexcept
         return "class";
     case cpp_template_keyword::keyword_typename:
         return "typename";
+    case cpp_template_keyword::concept_contraint:
+        return "concept constraint data lost";
     }
 
     return "should not get here";
@@ -22,10 +24,11 @@ const char* cppast::to_string(cpp_template_keyword kw) noexcept
 
 std::unique_ptr<cpp_template_type_parameter> cpp_template_type_parameter::build(
     const cpp_entity_index& idx, cpp_entity_id id, std::string name, cpp_template_keyword kw,
-    bool variadic, std::unique_ptr<cpp_type> default_type)
+    bool variadic, std::unique_ptr<cpp_type> default_type,
+    type_safe::optional<cpp_token_string> concept_constraint)
 {
     std::unique_ptr<cpp_template_type_parameter> result(
-        new cpp_template_type_parameter(std::move(name), kw, variadic, std::move(default_type)));
+        new cpp_template_type_parameter(std::move(name), kw, variadic, std::move(default_type), std::move(concept_constraint)));
     idx.register_definition(std::move(id), type_safe::cref(*result));
     return result;
 }

src/cpp_type.cpp

@@ -148,6 +148,7 @@ bool detail::cpp_type_ref_predicate::operator()(const cpp_entity& e)
     case cpp_entity_kind::function_template_specialization_t:
     case cpp_entity_kind::class_template_t:
     case cpp_entity_kind::class_template_specialization_t:
+    case cpp_entity_kind::concept_t:
     case cpp_entity_kind::static_assert_t:
     case cpp_entity_kind::unexposed_t:
     case cpp_entity_kind::count:

src/libclang/concept_parser.cpp

@@ -0,0 +1,62 @@
+// Copyright (C) 2017-2022 Jonathan Müller and cppast contributors
+// SPDX-License-Identifier: MIT
+
+#include <cppast/cpp_concept.hpp>
+
+#include <cppast/cpp_entity_kind.hpp>
+
+#include "libclang_visitor.hpp"
+#include "parse_functions.hpp"
+
+using namespace cppast;
+
+std::unique_ptr<cpp_entity> detail::try_parse_cpp_concept(const detail::parse_context& context,
+                                                          const CXCursor&              cur)
+{
+    DEBUG_ASSERT(cur.kind == CXCursor_UnexposedDecl, detail::assert_handler{});
+
+    detail::cxtokenizer    tokenizer(context.tu, context.file, cur);
+    detail::cxtoken_stream stream(tokenizer, cur);
+
+    if (!detail::skip_if(stream, "template"))
+        return nullptr;
+
+    if (stream.peek() != "<")
+        return nullptr;
+
+
+    auto closing_bracket_iter = detail::find_closing_bracket(stream);
+    auto params               = to_string(stream, closing_bracket_iter);
+
+    if (!detail::skip_if(stream, ">"))
+        return nullptr;
+
+    if (!detail::skip_if(stream, "concept"))
+        return nullptr;
+
+    const auto& identifier_token = stream.get();
+    if (identifier_token.kind() != CXTokenKind::CXToken_Identifier)
+    {
+        return nullptr;
+    }
+
+    cpp_concept::builder builder(identifier_token.value().std_str());
+
+    if (!detail::skip_if(stream, "="))
+    {
+        return nullptr;
+    }
+
+    if (*(stream.end() - 1) != ";")
+    {
+        return nullptr;
+    }
+
+    builder.set_expression(
+        parse_raw_expression(context, stream, stream.end() - 1,
+                             cpp_builtin_type::build(cpp_builtin_type_kind::cpp_bool)));
+
+    builder.set_parameters(std::move(params));
+
+    return builder.finish(*context.idx, detail::get_entity_id(cur));
+}

src/libclang/cxtokenizer.cpp

@@ -532,6 +532,38 @@ void detail::skip_brackets(detail::cxtoken_stream& stream)
     stream.set_cur(std::next(closing));
 }
 
+detail::cxtoken_iterator detail::find_sequence(detail::cxtoken_stream stream, detail::cxtoken_iterator start,
+                                               detail::cxtoken_iterator end)
+{
+    detail::cxtoken_iterator search_start = stream.cur();
+    while(search_start != stream.end())
+    {
+        detail::cxtoken_iterator search_iter = search_start;
+        detail::cxtoken_iterator seq_iter    = start;
+        bool                     failed      = false;
+
+        while(!failed && search_iter != stream.end() && seq_iter != end)
+        {
+            if(search_iter->value() != seq_iter->value()
+                || search_iter->kind() != seq_iter->kind())
+            {
+                failed = true;
+            }
+            else
+            {
+                ++search_iter;
+                ++seq_iter;
+            }
+        }
+        if(!failed)
+            return search_start;
+
+        ++search_start;
+    }
+
+    return stream.end();
+}
+
 namespace
 {
 type_safe::optional<std::string> parse_attribute_using(detail::cxtoken_stream& stream)

src/libclang/cxtokenizer.hpp

@@ -184,6 +184,10 @@ namespace detail
     // note: < might not work in the arguments of a template specialization
     void skip_brackets(cxtoken_stream& stream);
 
+    // finds the location of the given sequence in a stream
+    // returns an iterator to the first token of the found sequence, or stream.end() if not found
+    cxtoken_iterator find_sequence(cxtoken_stream stream, cxtoken_iterator start, cxtoken_iterator end);
+
     // parses attributes
     // if skip_anyway is true it will bump even if no attributes have been parsed
     cpp_attribute_list parse_attributes(cxtoken_stream& stream, bool skip_anyway = false);

src/libclang/parse_functions.cpp

@@ -125,6 +125,8 @@ try
         // go through all the try_parse_XXX functions
         if (auto entity = try_parse_cpp_language_linkage(context, cur))
             return entity;
+        if (auto entity = try_parse_cpp_concept(context, cur))
+            return entity;
         break;
 
     case CXCursor_MacroDefinition:

src/libclang/parse_functions.hpp

@@ -91,6 +91,11 @@ namespace detail
     // unexposed
     std::unique_ptr<cpp_entity> try_parse_cpp_language_linkage(const parse_context& context,
                                                                const CXCursor&      cur);
+    
+    //unexposed
+    std::unique_ptr<cpp_entity> try_parse_cpp_concept(const parse_context& context,
+                                                      const CXCursor&      cur);
+
     // CXXMethod
     std::unique_ptr<cpp_entity> try_parse_static_cpp_function(const parse_context& context,
                                                               const CXCursor&      cur);

src/libclang/template_parser.cpp

@@ -42,22 +42,64 @@ type_safe::optional<typename TemplateT::builder> get_builder(const detail::parse
         std::unique_ptr<EntityT>(static_cast<EntityT*>(entity.release())));
 }
 
+cpp_token_string extract_parameter_constraint(const detail::parse_context& context,
+    const CXCursor& parent,
+    detail::cxtoken_iterator target_range_start,
+    detail::cxtoken_iterator target_range_end)
+{
+    //search the parent context for the *exact* sequence in it's entirety
+    detail::cxtokenizer    tokenizer(context.tu, context.file, parent);
+    detail::cxtoken_stream stream(tokenizer, parent);
+    
+    detail::cxtoken_iterator found_start = detail::find_sequence(stream, target_range_start, target_range_end);
+    if(found_start == stream.end())
+        return detail::to_string(stream, stream.cur() + 1);
+
+    stream.set_cur(found_start);
+    stream.bump();
+    if (stream.peek() == "<")
+        detail::skip_brackets(stream);
+
+    detail::cxtoken_iterator constraint_end = stream.cur();
+    stream.set_cur(found_start);
+    //seek backwards until we are at the start of the qualified name
+    while(stream.peek().value() != "<" && stream.peek().value() != ",")
+    {
+        std::string str = stream.peek().value().std_str();
+        stream.bump_back();
+    }
+    stream.bump();
+    return detail::to_string(stream, constraint_end);
+}
+
 std::unique_ptr<cpp_template_parameter> parse_type_parameter(const detail::parse_context& context,
-                                                             const CXCursor&              cur)
+                                                             const CXCursor&              cur,
+                                                             const CXCursor&              parent)
 {
     DEBUG_ASSERT(clang_getCursorKind(cur) == CXCursor_TemplateTypeParameter,
                  detail::assert_handler{});
 
+
     detail::cxtokenizer    tokenizer(context.tu, context.file, cur);
     detail::cxtoken_stream stream(tokenizer, cur);
     auto                   name = detail::get_cursor_name(cur);
 
-    // syntax: typename/class [...] name [= ...]
+    // syntax: typename/class/constraint [...] name [= ...]
     auto                                  keyword    = cpp_template_keyword::keyword_class;
+    type_safe::optional<cpp_token_string> constraint = type_safe::nullopt;
+
     if (detail::skip_if(stream, "typename"))
         keyword = cpp_template_keyword::keyword_typename;
-    else
+    else if (!detail::skip_if(stream, "class"))
-        detail::skip(stream, "class");
+    {
+        keyword = cpp_template_keyword::concept_contraint;
+
+        //try to extract the constraint token string
+        constraint = extract_parameter_constraint(context, parent, stream.cur(), stream.end());
+        stream.bump();
+        if (stream.peek() == "<")
+            detail::skip_brackets(stream);
+    }
 
     auto variadic = false;
     if (detail::skip_if(stream, "..."))
@@ -72,7 +114,7 @@ std::unique_ptr<cpp_template_parameter> parse_type_parameter(const detail::parse
         def = detail::parse_raw_type(context, stream, stream.end());
 
     return cpp_template_type_parameter::build(*context.idx, detail::get_entity_id(cur),
-                                              name.c_str(), keyword, variadic, std::move(def));
+                                              name.c_str(), keyword, variadic, std::move(def), constraint);
 }
 
 std::unique_ptr<cpp_template_parameter> parse_non_type_parameter(
@@ -147,7 +189,7 @@ std::unique_ptr<cpp_template_template_parameter> parse_template_parameter(
     detail::visit_children(cur, [&](const CXCursor& child) {
         auto kind = clang_getCursorKind(child);
         if (kind == CXCursor_TemplateTypeParameter)
-            builder.add_parameter(parse_type_parameter(context, child));
+            builder.add_parameter(parse_type_parameter(context, child, cur));
         else if (kind == CXCursor_NonTypeTemplateParameter)
             builder.add_parameter(parse_non_type_parameter(context, child));
         else if (kind == CXCursor_TemplateTemplateParameter)
@@ -188,7 +230,7 @@ void parse_parameters(Builder& builder, const detail::parse_context& context, co
     detail::visit_children(cur, [&](const CXCursor& child) {
         auto kind = clang_getCursorKind(child);
         if (kind == CXCursor_TemplateTypeParameter)
-            builder.add_parameter(parse_type_parameter(context, child));
+            builder.add_parameter(parse_type_parameter(context, child, cur));
         else if (kind == CXCursor_NonTypeTemplateParameter)
             builder.add_parameter(parse_non_type_parameter(context, child));
         else if (kind == CXCursor_TemplateTemplateParameter)
@@ -389,3 +431,4 @@ std::unique_ptr<cpp_entity> detail::parse_cpp_class_template_specialization(
     return builder.finish(*context.idx, detail::get_entity_id(cur),
                           builder.get().class_().is_definition());
 }
+

src/visitor.cpp

@@ -112,6 +112,7 @@ bool detail::visit(const cpp_entity& e, detail::visitor_callback_t cb, void* fun
     case cpp_entity_kind::template_type_parameter_t:
     case cpp_entity_kind::non_type_template_parameter_t:
     case cpp_entity_kind::template_template_parameter_t:
+    case cpp_entity_kind::concept_t:
     case cpp_entity_kind::static_assert_t:
     case cpp_entity_kind::unexposed_t:
         return cb(functor, e, {visitor_info::leaf_entity, cur_access, last_child});

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);
+}