Workaround broken libclang version numbers

Closes #164.

Author: foonathan

src/libclang/concept_parser.cpp

@@ -13,12 +13,10 @@ using namespace cppast;
 std::unique_ptr<cpp_entity> detail::try_parse_cpp_concept(const detail::parse_context& context,
                                                           const CXCursor&              cur)
 {
-#if CINDEX_VERSION_MINOR >= 62
-    if (cur.kind != CXCursor_ConceptDecl)
+    DEBUG_ASSERT(cur.kind == CXCursor_UnexposedDecl || cur.kind == CXCursor_ConceptDecl,
+                 detail::assert_handler{});
+    if (libclang_definitely_has_concept_support && cur.kind != CXCursor_ConceptDecl)
         return nullptr;
-#else
-    DEBUG_ASSERT(cur.kind == CXCursor_UnexposedDecl, detail::assert_handler{});
-#endif
 
     detail::cxtokenizer    tokenizer(context.tu, context.file, cur);
     detail::cxtoken_stream stream(tokenizer, cur);

src/libclang/parse_functions.cpp

@@ -119,7 +119,7 @@ try
     }
 
     auto kind = clang_getCursorKind(cur);
-    switch (kind)
+    switch (int(kind))
     {
     case CXCursor_UnexposedDecl:
         // go through all the try_parse_XXX functions
@@ -198,13 +198,10 @@ try
     case CXCursor_ClassTemplatePartialSpecialization:
         return parse_cpp_class_template_specialization(context, cur);
 
-#if CINDEX_VERSION_MINOR >= 62
-    case CXCursor_ConceptDecl:
-        return try_parse_cpp_concept(context, cur);
-#endif
-
     case CXCursor_StaticAssert:
         return parse_cpp_static_assert(context, cur);
+    case CXCursor_ConceptDecl:
+        return try_parse_cpp_concept(context, cur);
 
     default:
         break;

src/libclang/parse_functions.hpp

@@ -94,7 +94,18 @@ namespace detail
     std::unique_ptr<cpp_entity> try_parse_cpp_language_linkage(const parse_context& context,
                                                                const CXCursor&      cur);
 
-    // unexposed
+    // If the version is < 62, CXCursor_ConceptDecl does not exist.
+    // If the version is > 62, CXCursor_ConceptDecl does exist.
+    // If the version == 62, it may or may not exist. :(
+    // As such, manually define it to the corresponding number.
+    constexpr auto libclang_definitely_has_concept_support = CINDEX_VERSION_MINOR > 62;
+#if CINDEX_VERSION_MINOR > 62
+    constexpr auto CXCursor_ConceptDecl = ::CXCursor_ConceptDecl;
+#else
+    constexpr auto CXCursor_ConceptDecl = CXCursorKind(604);
+#endif
+
+    // unexposed, ConceptDecl
     std::unique_ptr<cpp_entity> try_parse_cpp_concept(const parse_context& context,
                                                       const CXCursor&      cur);