Implement basic concept parsing

- requires clauses are collected into a Value and not interpreted at
  this time

Author: virtuald

cxxheaderparser/lexer.py

@@ -83,6 +83,7 @@ class PlyLexer:
         "char16_t",
         "char32_t",
         "class",
+        "concept",
         "const",
         "constexpr",
         "const_cast",
@@ -121,6 +122,7 @@ class PlyLexer:
         "public",
         "register",
         "reinterpret_cast",
+        "requires",
         "return",
         "short",
         "signed",

cxxheaderparser/parser.py

@@ -22,6 +22,7 @@
     AutoSpecifier,
     BaseClass,
     ClassDecl,
+    Concept,
     DecltypeSpecifier,
     DecoratedType,
     EnumDecl,
@@ -537,7 +538,7 @@ def _on_block_end(self, tok: LexToken, doxygen: typing.Optional[str]) -> None:
             self._finish_class_decl(old_state)
 
     #
-    # Template parsing
+    # Template and concept parsing
     #
 
     def _parse_template_type_parameter(
@@ -640,6 +641,8 @@ def _parse_template(self, tok: LexToken, doxygen: typing.Optional[str]) -> None:
             self._parse_using(tok, doxygen, template)
         elif tok.type == "friend":
             self._parse_friend_decl(tok, doxygen, template)
+        elif tok.type == "concept":
+            self._parse_concept(tok, doxygen, template)
         else:
             self._parse_declarations(tok, doxygen, template)
 
@@ -750,6 +753,32 @@ def _parse_template_instantiation(
             self.state, TemplateInst(typename, extern, doxygen)
         )
 
+    def _parse_concept(
+        self,
+        tok: LexToken,
+        doxygen: typing.Optional[str],
+        template: TemplateDecl,
+    ) -> None:
+        name = self._next_token_must_be("NAME")
+        self._next_token_must_be("=")
+
+        # not trying to understand this for now
+        raw_constraint = self._create_value(self._consume_value_until([], ",", ";"))
+
+        state = self.state
+        if isinstance(state, ClassBlockState):
+            raise CxxParseError("concept cannot be defined in a class")
+
+        self.visitor.on_concept(
+            state,
+            Concept(
+                template=template,
+                name=name.value,
+                raw_constraint=raw_constraint,
+                doxygen=doxygen,
+            ),
+        )
+
     #
     # Attributes
     #

cxxheaderparser/simple.py

@@ -34,6 +34,7 @@
 
 from .types import (
     ClassDecl,
+    Concept,
     EnumDecl,
     Field,
     ForwardDecl,
@@ -113,6 +114,9 @@ class NamespaceScope:
     using_alias: typing.List[UsingAlias] = field(default_factory=list)
     ns_alias: typing.List[NamespaceAlias] = field(default_factory=list)
 
+    #: Concepts
+    concepts: typing.List[Concept] = field(default_factory=list)
+
     #: Explicit template instantiations
     template_insts: typing.List[TemplateInst] = field(default_factory=list)
 
@@ -243,6 +247,9 @@ def on_namespace_start(self, state: SNamespaceBlockState) -> typing.Optional[boo
     def on_namespace_end(self, state: SNamespaceBlockState) -> None:
         pass
 
+    def on_concept(self, state: SNonClassBlockState, concept: Concept) -> None:
+        state.user_data.concepts.append(concept)
+
     def on_namespace_alias(
         self, state: SNonClassBlockState, alias: NamespaceAlias
     ) -> None:

cxxheaderparser/types.py

@@ -551,6 +551,31 @@ class TemplateInst:
     doxygen: typing.Optional[str] = None
 
 
+@dataclass
+class Concept:
+    """
+    Preliminary support for consuming headers that contain concepts, but
+    not trying to actually make sense of them at this time. If this is
+    something you care about, pull requests are welcomed!
+
+    .. code-block:: c++
+
+        template <class T>
+        concept Meowable = is_meowable<T>;
+
+        template<typename T>
+        concept Addable = requires (T x) { x + x; };
+    """
+
+    template: TemplateDecl
+    name: str
+
+    #: In the future this will be removed if we fully parse the expression
+    raw_constraint: Value
+
+    doxygen: typing.Optional[str] = None
+
+
 @dataclass
 class ForwardDecl:
     """

cxxheaderparser/visitor.py

@@ -8,6 +8,7 @@
 
 
 from .types import (
+    Concept,
     EnumDecl,
     Field,
     ForwardDecl,
@@ -89,6 +90,14 @@ def on_namespace_alias(
         Called when a ``namespace`` alias is encountered
         """
 
+    def on_concept(self, state: NonClassBlockState, concept: Concept) -> None:
+        """
+        .. code-block:: c++
+
+            template <class T>
+            concept Meowable = is_meowable<T>;
+        """
+
     def on_forward_decl(self, state: State, fdecl: ForwardDecl) -> None:
         """
         Called when a forward declaration is encountered
@@ -254,6 +263,9 @@ def on_namespace_start(self, state: NamespaceBlockState) -> typing.Optional[bool
     def on_namespace_end(self, state: NamespaceBlockState) -> None:
         return None
 
+    def on_concept(self, state: NonClassBlockState, concept: Concept) -> None:
+        return None
+
     def on_namespace_alias(
         self, state: NonClassBlockState, alias: NamespaceAlias
     ) -> None: