[clang][ExtractAPI] Add support for C++ class templates and concepts

[evelez7]

Summary

Add has_template template, DeclarationFragmentBuilder functions, and tests for class templates, specializations/partial specs, and concepts.

Depends on D157007

[evelez7]

Format DeclarationFragments.h, try to address buildbot fail on clang-format

[evelez7]

Add documentation to template argument name deduction, add missing method declarations to visitor base

[evelez7]

Abstract the name deduction for generic template args to its own function. It's very helpful in other cases.

[evelez7]

Refactor template arg name deduction to get as string for FragmentKind::typeIdentifier

[evelez7]

Add brackets for SerializerBase visit methods

[evelez7]

Fix template arg identification

[dang]

Looks mostly good. Quick Question how do we handle inheritance to a template parameter?

clang/include/clang/ExtractAPI/API.h

665

Minor nit, I would prefer for Specialization to be fully spelled out.

clang/include/clang/ExtractAPI/DeclarationFragments.h

192

This is really a model type and should live either in it's own file or in API.h

314

I feel this should be a constructor for Template seeing that this never fails.

clang/include/clang/ExtractAPI/ExtractAPIVisitor.h

435

Where is the cast?

clang/lib/ExtractAPI/DeclarationFragments.cpp

754

is this clang-format formatted?

784

Kinda sad we have to do this. I guess there is no easy way to change the AST to support this?

[evelez7]

Address review feedback

• Handle inheriting from a template parameter.
• Add a new test to check inheriting from a template parameter.
• Move base class gathering to a new private method for code reuse.
• Move Template class to API.h and convert getTemplate functions to constructors.
• Rename all instances of Spec to Specialization.

[evelez7]

We didn't handle inheriting from a template parameter, but now we do by serializing the relationship. The parameter does not produce a target USR so it falls back to its name.

clang/include/clang/ExtractAPI/DeclarationFragments.h

192

Moved to API.h

clang/lib/ExtractAPI/DeclarationFragments.cpp

754

Yes.

784

I've just realized that we could just take the the template parameter and insert it arbitrarily but it could easily be the incorrect partial specialization. We'd still need to determine which argument corresponds to the template param.

One optimization is to check if there is only one new param in a partial specialization so that a var template's type is automatically known if it is the new template param, i.e. template<typename T> T x<T, int>

The unfortunate reality is that template parameters are actual Decls (TemplateTypeParmDecl, which do hold the generic's correct name), and TemplateArguments are not. Calling TemplateArgument.getAsDecl() or getAsTemplate always result in assertion errors (when the arg is a template param) since there are no analogous structures. There'd have to be a TemplateTypeArgDecl.

[evelez7]

Also rename traverseSpec* in SerializerBase.h

[dang]

LGTM

[evelez7]

Fix formatting for introduced declarations in DeclarationFragments.h

clang/include/clang/ExtractAPI/API.h

enum RecordKind {
     RK_EnumConstant,
     RK_Enum,
     RK_StructField,
     RK_Struct,
     RK_Union,
     RK_StaticField,
     RK_CXXField,
     RK_CXXClass,
+    RK_ClassTemplate,
+    RK_ClassTemplateSpecialization,
+    RK_ClassTemplatePartialSpecialization,
+    RK_Concept,
     RK_CXXStaticMethod,
     RK_CXXInstanceMethod,
     RK_CXXConstructorMethod,
     RK_CXXDestructorMethod,
     RK_ObjCInstanceProperty,
     RK_ObjCClassProperty,
     RK_ObjCIvar,
     RK_ObjCClassMethod,
struct CXXClassRecord : APIRecord {
   static bool classof(const APIRecord *Record) {
     return (Record->getKind() == RK_CXXClass);
   }
 
 private:
   virtual void anchor();
 };
 
+struct ClassTemplateRecord : CXXClassRecord {
+  Template Templ;
+
+  ClassTemplateRecord(StringRef USR, StringRef Name, PresumedLoc Loc,
+                      AvailabilitySet Availabilities, const DocComment &Comment,
+                      DeclarationFragments Declaration,
+                      DeclarationFragments SubHeading, Template Template,
+                      bool IsFromSystemHeader)
+      : CXXClassRecord(USR, Name, Loc, std::move(Availabilities), Comment,
+                       Declaration, SubHeading, RK_ClassTemplate,
+                       IsFromSystemHeader),
+        Templ(Template) {}
+
+  static bool classof(const APIRecord *Record) {
+    return Record->getKind() == RK_ClassTemplate;
+  }
+};
+
+struct ClassTemplateSpecRecord : CXXClassRecord {
+  ClassTemplateSpecRecord(StringRef USR, StringRef Name, PresumedLoc Loc,
+                          AvailabilitySet Availabilities,
+                          const DocComment &Comment,
+                          DeclarationFragments Declaration,
+                          DeclarationFragments SubHeading,
+                          bool IsFromSystemHeader)
+      : CXXClassRecord(USR, Name, Loc, std::move(Availabilities), Comment,
+                       Declaration, SubHeading, RK_ClassTemplateSpecialization,
+                       IsFromSystemHeader) {}
+
+  static bool classof(const APIRecord *Record) {
+    return Record->getKind() == RK_ClassTemplateSpecialization;
+  }
+};
+
+struct ClassTemplatePartialSpecRecord : CXXClassRecord {
+  Template Templ;
+  ClassTemplatePartialSpecRecord(StringRef USR, StringRef Name, PresumedLoc Loc,
+                                 AvailabilitySet Availabilities,
+                                 const DocComment &Comment,
+                                 DeclarationFragments Declaration,
+                                 DeclarationFragments SubHeading,
+                                 Template Template, bool IsFromSystemHeader)
+      : CXXClassRecord(USR, Name, Loc, std::move(Availabilities), Comment,
+                       Declaration, SubHeading, RK_ClassTemplateSpecialization,
+                       IsFromSystemHeader),
+        Templ(Template) {}
+
+  static bool classof(const APIRecord *Record) {
+    return Record->getKind() == RK_ClassTemplatePartialSpecialization;
+  }
+};
+
+struct ConceptRecord : APIRecord {
+  Template Templ;
+  ConceptRecord(StringRef USR, StringRef Name, PresumedLoc Loc,
+                AvailabilitySet Availabilities, const DocComment &Comment,
+                DeclarationFragments Declaration,
+                DeclarationFragments SubHeading, Template Template,
+                bool IsFromSystemHeader)
+      : APIRecord(RK_Concept, USR, Name, Loc, std::move(Availabilities),
+                  LinkageInfo::none(), Comment, Declaration, SubHeading,
+                  IsFromSystemHeader),
+        Templ(Template) {}
+
+  static bool classof(const APIRecord *Record) {
+    return Record->getKind() == RK_Concept;
+  }
+};
+
 /// This holds information associated with Objective-C categories.
 struct ObjCCategoryRecord : ObjCContainerRecord {
   SymbolReference Interface;
 
   ObjCCategoryRecord(StringRef USR, StringRef Name, PresumedLoc Loc,
                      AvailabilitySet Availabilities, const DocComment &Comment,
                      DeclarationFragments Declaration,
                      DeclarationFragments SubHeading, SymbolReference Interface,

 struct has_function_signature<ObjCClassMethodRecord> : public std::true_type {};
 template <>
 struct has_function_signature<CXXMethodRecord> : public std::true_type {};
 
 template <typename RecordTy> struct has_access : public std::false_type {};
 template <> struct has_access<CXXMethodRecord> : public std::true_type {};
 template <> struct has_access<CXXFieldRecord> : public std::true_type {};
 
+template <typename RecordTy> struct has_template : public std::false_type {};
+template <> struct has_template<ClassTemplateRecord> : public std::true_type {};
+template <>
+struct has_template<ClassTemplatePartialSpecRecord> : public std::true_type {};
+template <> struct has_template<ConceptRecord> : public std::true_type {};
+
 /// APISet holds the set of API records collected from given inputs.
 class APISet {
 public:
   /// Create and add a global variable record into the API set.
   ///
   /// Note: the caller is responsible for keeping the StringRef \p Name and
   /// \p USR alive. APISet::copyString provides a way to copy strings into
   /// APISet itself, and APISet::recordUSR(const Decl *D) is a helper method
CXXFieldRecord *addCXXField(CXXClassRecord *CXXClass, StringRef Name,
                               AccessControl Access, bool IsFromSystemHeader);
 
   CXXClassRecord *
   addCXXClass(StringRef Name, StringRef USR, PresumedLoc Loc,
               AvailabilitySet Availability, const DocComment &Comment,
               DeclarationFragments Declaration, DeclarationFragments SubHeading,
               APIRecord::RecordKind Kind, bool IsFromSystemHeader);
 
+  ClassTemplateRecord *
+  addClassTemplate(StringRef Name, StringRef USR, PresumedLoc Loc,
+                   AvailabilitySet Availability, const DocComment &Comment,
+                   DeclarationFragments Declaration,
+                   DeclarationFragments SubHeading, Template Template,
+                   bool IsFromSystemHeader);
+
+  ClassTemplateSpecRecord *
+  addClassTemplateSpec(StringRef Name, StringRef USR, PresumedLoc Loc,
+                       AvailabilitySet Availability, const DocComment &Comment,
+                       DeclarationFragments Declaration,
+                       DeclarationFragments SubHeading,
+                       bool IsFromSystemHeader);
+
+  ClassTemplatePartialSpecRecord *addClassTemplatePartialSpec(
+      StringRef Name, StringRef USR, PresumedLoc Loc,
+      AvailabilitySet Availability, const DocComment &Comment,
+      DeclarationFragments Declaration, DeclarationFragments SubHeading,
+      Template Template, bool IsFromSystemHeader);
+
   CXXMethodRecord *
   addCXXMethod(CXXClassRecord *CXXClassRecord, StringRef Name, StringRef USR,
                PresumedLoc Loc, AvailabilitySet Availability,
                const DocComment &Comment, DeclarationFragments Declaration,
                DeclarationFragments SubHeading, FunctionSignature Signature,
                bool IsStatic, AccessControl Access, bool IsFromSystemHeader);
 
   CXXMethodRecord *addCXXSpecialMethod(
       CXXClassRecord *CXXClassRecord, StringRef Name, StringRef USR,
       PresumedLoc Loc, AvailabilitySet Availability, const DocComment &Comment,
       DeclarationFragments Declaration, DeclarationFragments SubHeading,
       FunctionSignature Signature, bool IsConstructor, AccessControl Access,
       bool IsFromSystemHeader);
 
+  ConceptRecord *addConcept(StringRef Name, StringRef USR, PresumedLoc Loc,
+                            AvailabilitySet Availability,
+                            const DocComment &Comment,
+                            DeclarationFragments Declaration,
+                            DeclarationFragments SubHeading, Template Template,
+                            bool IsFromSystemHeader);
+
   /// Create and add an Objective-C category record into the API set.
   ///
   /// Note: the caller is responsible for keeping the StringRef \p Name and
   /// \p USR alive. APISet::copyString provides a way to copy strings into
   /// APISet itself, and APISet::recordUSR(const Decl *D) is a helper method
   /// to generate the USR for \c D and keep it alive in APISet.
   ObjCCategoryRecord *
   addObjCCategory(StringRef Name, StringRef USR, PresumedLoc Loc,
const RecordMap<GlobalVariableRecord> &getGlobalVariables() const {
     return GlobalVariables;
   }
   const RecordMap<StaticFieldRecord> &getStaticFields() const {
     return StaticFields;
   }
   const RecordMap<EnumRecord> &getEnums() const { return Enums; }
   const RecordMap<StructRecord> &getStructs() const { return Structs; }
   const RecordMap<CXXClassRecord> &getCXXClasses() const { return CXXClasses; }
+  const RecordMap<ConceptRecord> &getConcepts() const { return Concepts; }
+  const RecordMap<ClassTemplateRecord> &getClassTemplates() const {
+    return ClassTemplates;
+  }
+  const RecordMap<ClassTemplateSpecRecord> &
+  getClassTemplateSpecializations() const {
+    return ClassTemplateSpecializations;
+  }
+  const RecordMap<ClassTemplatePartialSpecRecord> &
+  getClassTemplatePartialSpecializations() const {
+    return ClassTemplatePartialSpecializations;
+  }
+  const RecordMap<ConceptRecord> &getRecords() const { return Concepts; }
   const RecordMap<ObjCCategoryRecord> &getObjCCategories() const {
     return ObjCCategories;
   }
   const RecordMap<ObjCInterfaceRecord> &getObjCInterfaces() const {
     return ObjCInterfaces;
   }
   const RecordMap<ObjCProtocolRecord> &getObjCProtocols() const {
     return ObjCProtocols;
private:
   llvm::BumpPtrAllocator StringAllocator;
 
   const llvm::Triple Target;
   const Language Lang;
 
   llvm::DenseMap<StringRef, APIRecord *> USRBasedLookupTable;
   RecordMap<GlobalFunctionRecord> GlobalFunctions;
   RecordMap<GlobalVariableRecord> GlobalVariables;
+  RecordMap<ConceptRecord> Concepts;
   RecordMap<StaticFieldRecord> StaticFields;
   RecordMap<EnumRecord> Enums;
   RecordMap<StructRecord> Structs;
   RecordMap<CXXClassRecord> CXXClasses;
+  RecordMap<ClassTemplateRecord> ClassTemplates;
+  RecordMap<ClassTemplateSpecRecord> ClassTemplateSpecializations;
+  RecordMap<ClassTemplatePartialSpecRecord> ClassTemplatePartialSpecializations;
   RecordMap<ObjCCategoryRecord> ObjCCategories;
   RecordMap<ObjCInterfaceRecord> ObjCInterfaces;
   RecordMap<ObjCProtocolRecord> ObjCProtocols;
   RecordMap<MacroDefinitionRecord> Macros;
   RecordMap<TypedefRecord> Typedefs;
 
 public:
   const std::string ProductName;
 };
 
 } // namespace extractapi
 } // namespace clang
 
 #endif // LLVM_CLANG_EXTRACTAPI_API_H

clang/include/clang/ExtractAPI/DeclarationFragments.h

 
 #ifndef LLVM_CLANG_EXTRACTAPI_DECLARATION_FRAGMENTS_H
 #define LLVM_CLANG_EXTRACTAPI_DECLARATION_FRAGMENTS_H
 
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclObjC.h"
+#include "clang/AST/DeclTemplate.h"
 #include "clang/Lex/MacroInfo.h"
 #include "llvm/ADT/StringRef.h"
 #include <vector>
 
 namespace clang {
 namespace extractapi {
 
 /// DeclarationFragments is a vector of tagged important parts of a symbol's
public:
   DeclarationFragments &append(DeclarationFragments &&Other) {
     Fragments.insert(Fragments.end(),
                      std::make_move_iterator(Other.Fragments.begin()),
                      std::make_move_iterator(Other.Fragments.end()));
     Other.Fragments.clear();
     return *this;
   }
 
+  DeclarationFragments &pop_back()
+  {
+    Fragments.pop_back();
+    return *this;
+  }
+
   /// Append a text Fragment of a space character.
   ///
   /// \returns a reference to the DeclarationFragments object itself after
   /// appending to chain up consecutive appends.
   DeclarationFragments &appendSpace();
 
   /// Get the string description of a FragmentKind \p Kind.
   static StringRef getFragmentKindString(FragmentKind Kind);
 
   /// Get the corresponding FragmentKind from string \p S.
   static FragmentKind parseFragmentKindFromString(StringRef S);
 
   static DeclarationFragments
   getExceptionSpecificationString(ExceptionSpecificationType ExceptionSpec);
 
   static DeclarationFragments getStructureTypeFragment(const RecordDecl *Decl);
 
 private:
   std::vector<Fragment> Fragments;
 };
 
+class Template {
+  struct TemplateParameter {
+    // "class", "typename", or concept name
+    std::string Type;
+    std::string Name;
+    unsigned int Index;
+    unsigned int Depth;
+    bool IsParameterPack;
+
+    TemplateParameter(std::string Type, std::string Name, unsigned int Index,
+                      unsigned int Depth, bool IsParameterPack)
+        : Type(Type), Name(Name), Index(Index), Depth(Depth),
+          IsParameterPack(IsParameterPack) {}
+  };
+
+  struct TemplateConstraint {
+    // type name of the constraint, if it has one
+    std::string Type;
+    std::string Kind;
+    std::string LHS, RHS;
+  };
+  SmallVector<TemplateParameter> Parameters;
+  SmallVector<TemplateConstraint> Constraints;
+
+public:
+  Template() = default;
+
+  const SmallVector<TemplateParameter> &getParameters() const {
+    return Parameters;
+  }
+
+  const SmallVector<TemplateConstraint> &getConstraints() const {
+    return Constraints;
+  }
+
+  void addTemplateParameter(std::string Type, std::string Name,
+                            unsigned int Index, unsigned int Depth,
+                            bool IsParameterPack) {
+    Parameters.emplace_back(Type, Name, Index, Depth, IsParameterPack);
+  }
+
+  bool empty() const { return Parameters.empty() && Constraints.empty(); }
+};
+
 class AccessControl {
 public:
   AccessControl(std::string Access) : Access(Access) {}
 
   const std::string &getAccess() const { return Access; }
 
   bool empty() const { return Access.empty(); }
 
static AccessControl getAccessControl(const Decl *Decl) {
     case AS_protected:
       return AccessControl("protected");
     case AS_none:
       return AccessControl("none");
     }
     llvm_unreachable("Unhandled access control");
   }
 
+  /// Get template details from a template function, class, or variable
+  static Template getTemplate(const TemplateDecl *Decl) {
+    Template Template;
+    for (auto *const Parameter : *Decl->getTemplateParameters()) {
+      const auto *Param = dyn_cast<TemplateTypeParmDecl>(Parameter);
+      if (!Param) // some params are null
+        continue;
+      std::string Type;
+      if (Param->hasTypeConstraint())
+        Type = Param->getTypeConstraint()->getNamedConcept()->getName().str();
+      else if (Param->wasDeclaredWithTypename())
+        Type = "typename";
+      else
+        Type = "class";
+
+      Template.addTemplateParameter(Type, Param->getName().str(),
+                                    Param->getIndex(), Param->getDepth(),
+                                    Param->isParameterPack());
+    }
+    return Template;
+  }
+
+  static Template
+  getTemplate(const ClassTemplatePartialSpecializationDecl *Decl) {
+    Template Template;
+    for (auto *const Parameter : *Decl->getTemplateParameters()) {
+      const auto *Param = dyn_cast<TemplateTypeParmDecl>(Parameter);
+      if (!Param) // some params are null
+        continue;
+      std::string Type;
+      if (Param->hasTypeConstraint())
+        Type = Param->getTypeConstraint()->getNamedConcept()->getName().str();
+      else if (Param->wasDeclaredWithTypename())
+        Type = "typename";
+      else
+        Type = "class";
+
+      Template.addTemplateParameter(Type, Param->getName().str(),
+                                    Param->getIndex(), Param->getDepth(),
+                                    Param->isParameterPack());
+    }
+    return Template;
+  }
+
   /// Build DeclarationFragments for a variable declaration VarDecl.
   static DeclarationFragments getFragmentsForVar(const VarDecl *);
 
   /// Build DeclarationFragments for a function declaration FunctionDecl.
   static DeclarationFragments getFragmentsForFunction(const FunctionDecl *);
 
   /// Build DeclarationFragments for an enum constant declaration
   /// EnumConstantDecl.
public:
   static DeclarationFragments getFragmentsForCXXMethod(const CXXMethodDecl *);
 
   static DeclarationFragments
   getFragmentsForConversionFunction(const CXXConversionDecl *);
 
   static DeclarationFragments
   getFragmentsForOverloadedOperator(const CXXMethodDecl *);
 
+  static DeclarationFragments
+      getFragmentsForTemplateParameters(ArrayRef<NamedDecl *>);
+
+  static DeclarationFragments
+  getFragmentsForTemplateArguments(const ArrayRef<TemplateArgument>,
+                                   const std::optional<ArrayRef<NamedDecl *>>);
+
+  static DeclarationFragments getFragmentsForConcept(const ConceptDecl *);
+
+  static DeclarationFragments
+  getFragmentsForRedeclarableTemplate(const RedeclarableTemplateDecl *);
+
+  static DeclarationFragments getFragmentsForClassTemplateSpecialization(
+      const ClassTemplateSpecializationDecl *);
+
+  static DeclarationFragments getFragmentsForClassTemplatePartialSpecialization(
+      const ClassTemplatePartialSpecializationDecl *);
+
   /// Build DeclarationFragments for an Objective-C category declaration
   /// ObjCCategoryDecl.
   static DeclarationFragments
   getFragmentsForObjCCategory(const ObjCCategoryDecl *);
 
   /// Build DeclarationFragments for an Objective-C interface declaration
   /// ObjCInterfaceDecl.
   static DeclarationFragments

clang/include/clang/ExtractAPI/ExtractAPIVisitor.h

 /// This file defines the ExtractAPVisitor AST visitation interface.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_EXTRACTAPI_EXTRACT_API_VISITOR_H
 #define LLVM_CLANG_EXTRACTAPI_EXTRACT_API_VISITOR_H
 
 #include "clang/AST/DeclCXX.h"
+#include "clang/AST/DeclTemplate.h"
 #include "clang/Basic/OperatorKinds.h"
 #include "clang/Basic/Specifiers.h"
 #include "clang/ExtractAPI/DeclarationFragments.h"
 #include "llvm/ADT/FunctionExtras.h"
 
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ParentMapContext.h"
 #include "clang/AST/RecursiveASTVisitor.h"
public:
   bool VisitFunctionDecl(const FunctionDecl *Decl);
 
   bool VisitEnumDecl(const EnumDecl *Decl);
 
   bool WalkUpFromRecordDecl(const RecordDecl *Decl);
 
   bool WalkUpFromCXXRecordDecl(const CXXRecordDecl *Decl);
 
+  bool WalkUpFromClassTemplateSpecializationDecl(
+      const ClassTemplateSpecializationDecl *Decl);
+
+  bool WalkUpFromClassTemplatePartialSpecializationDecl(
+      const ClassTemplatePartialSpecializationDecl *Decl);
+
   bool VisitRecordDecl(const RecordDecl *Decl);
 
   bool VisitCXXRecordDecl(const CXXRecordDecl *Decl);
 
+  bool VisitConceptDecl(const ConceptDecl *Decl);
+
+  bool VisitClassTemplateSpecializationDecl(
+      const ClassTemplateSpecializationDecl *Decl);
+
+  bool VisitClassTemplatePartialSpecializationDecl(
+      const ClassTemplatePartialSpecializationDecl *Decl);
+
   bool VisitObjCInterfaceDecl(const ObjCInterfaceDecl *Decl);
 
   bool VisitObjCProtocolDecl(const ObjCProtocolDecl *Decl);
 
   bool VisitTypedefNameDecl(const TypedefNameDecl *Decl);
 
   bool VisitObjCCategoryDecl(const ObjCCategoryDecl *Decl);
 

 template <typename Derived>
 bool ExtractAPIVisitorBase<Derived>::WalkUpFromCXXRecordDecl(
     const CXXRecordDecl *Decl) {
   getDerivedExtractAPIVisitor().VisitCXXRecordDecl(Decl);
   return true;
 }
 
 template <typename Derived>
+bool ExtractAPIVisitorBase<Derived>::WalkUpFromClassTemplateSpecializationDecl(
+    const ClassTemplateSpecializationDecl *Decl) {
+  getDerivedExtractAPIVisitor().VisitClassTemplateSpecializationDecl(Decl);
+  return true;
+}
+
+template <typename Derived>
+bool ExtractAPIVisitorBase<Derived>::
+    WalkUpFromClassTemplatePartialSpecializationDecl(
+        const ClassTemplatePartialSpecializationDecl *Decl) {
+  getDerivedExtractAPIVisitor().VisitClassTemplatePartialSpecializationDecl(
+      Decl);
+  return true;
+}
+
+template <typename Derived>
 bool ExtractAPIVisitorBase<Derived>::VisitRecordDecl(const RecordDecl *Decl) {
   if (!getDerivedExtractAPIVisitor().shouldDeclBeIncluded(Decl))
     return true;
   // Collect symbol information.
   StringRef Name = Decl->getName();
   if (Name.empty())
     Name = getTypedefName(Decl);
   if (Name.empty())
getDerivedExtractAPIVisitor().recordStructFields(StructRecord,
                                                    Decl->fields());
 
   return true;
 }
 
 template <typename Derived>
 bool ExtractAPIVisitorBase<Derived>::VisitCXXRecordDecl(
     const CXXRecordDecl *Decl) {
-  if (!getDerivedExtractAPIVisitor().shouldDeclBeIncluded(Decl))
+  if (!getDerivedExtractAPIVisitor().shouldDeclBeIncluded(Decl) ||
+      Decl->isImplicit())
     return true;
 
   StringRef Name = Decl->getName();
   StringRef USR = API.recordUSR(Decl);
   PresumedLoc Loc =
       Context.getSourceManager().getPresumedLoc(Decl->getLocation());
   DocComment Comment;
   if (auto *RawComment =
           getDerivedExtractAPIVisitor().fetchRawCommentForDecl(Decl))
     Comment = RawComment->getFormattedLines(Context.getSourceManager(),
                                             Context.getDiagnostics());
   DeclarationFragments Declaration =
       DeclarationFragmentsBuilder::getFragmentsForCXXClass(Decl);
   DeclarationFragments SubHeading =
       DeclarationFragmentsBuilder::getSubHeading(Decl);
 
   APIRecord::RecordKind Kind;
   if (Decl->isUnion())
     Kind = APIRecord::RecordKind::RK_Union;
   else if (Decl->isStruct())
     Kind = APIRecord::RecordKind::RK_Struct;
   else
     Kind = APIRecord::RecordKind::RK_CXXClass;
 
-  CXXClassRecord *CXXClassRecord =
+  CXXClassRecord *CXXClassRecord;
+  if (Decl->getDescribedClassTemplate()) {
+    // Inject template fragments before class fragments.
+    Declaration.insert(
+        Declaration.begin(),
+        DeclarationFragmentsBuilder::getFragmentsForRedeclarableTemplate(
+            Decl->getDescribedClassTemplate()));
+    // Cast to easily use previous declaration to get bases.
+    CXXClassRecord = API.addClassTemplate(
+        Name, USR, Loc, AvailabilitySet(Decl), Comment, Declaration, SubHeading,
+        DeclarationFragmentsBuilder::getTemplate(
+            Decl->getDescribedClassTemplate()),
+        isInSystemHeader(Decl));
+  } else
+    CXXClassRecord =
         API.addCXXClass(Name, USR, Loc, AvailabilitySet(Decl), Comment,
                         Declaration, SubHeading, Kind, isInSystemHeader(Decl));
 
   // FIXME: store AccessSpecifier given by inheritance
   for (const auto BaseSpecifier : Decl->bases()) {
     // skip classes not inherited as public
     if (BaseSpecifier.getAccessSpecifier() != AccessSpecifier::AS_public)
       continue;
     SymbolReference BaseClass;
     CXXRecordDecl *BaseClassDecl =
         BaseSpecifier.getType().getTypePtr()->getAsCXXRecordDecl();
     BaseClass.Name = BaseClassDecl->getName();
     BaseClass.USR = API.recordUSR(BaseClassDecl);
     CXXClassRecord->Bases.emplace_back(BaseClass);
   }
 
   getDerivedExtractAPIVisitor().recordCXXFields(CXXClassRecord, Decl->fields());
   getDerivedExtractAPIVisitor().recordCXXMethods(CXXClassRecord,
                                                  Decl->methods());
   return true;
 }
 
 template <typename Derived>
+bool ExtractAPIVisitorBase<Derived>::VisitConceptDecl(const ConceptDecl *Decl) {
+  if (!getDerivedExtractAPIVisitor().shouldDeclBeIncluded(Decl))
+    return true;
+
+  StringRef Name = Decl->getName();
+  StringRef USR = API.recordUSR(Decl);
+  PresumedLoc Loc =
+      Context.getSourceManager().getPresumedLoc(Decl->getLocation());
+  DocComment Comment;
+  if (auto *RawComment =
+          getDerivedExtractAPIVisitor().fetchRawCommentForDecl(Decl))
+    Comment = RawComment->getFormattedLines(Context.getSourceManager(),
+                                            Context.getDiagnostics());
+  DeclarationFragments Declaration =
+      DeclarationFragmentsBuilder::getFragmentsForConcept(Decl);
+  DeclarationFragments SubHeading =
+      DeclarationFragmentsBuilder::getSubHeading(Decl);
+  API.addConcept(Name, USR, Loc, AvailabilitySet(Decl), Comment, Declaration,
+                 SubHeading, DeclarationFragmentsBuilder::getTemplate(Decl),
+                 isInSystemHeader(Decl));
+  return true;
+}
+
+template <typename Derived>
+bool ExtractAPIVisitorBase<Derived>::VisitClassTemplateSpecializationDecl(
+    const ClassTemplateSpecializationDecl *Decl) {
+  if (!getDerivedExtractAPIVisitor().shouldDeclBeIncluded(Decl))
+    return true;
+
+  StringRef Name = Decl->getName();
+  StringRef USR = API.recordUSR(Decl);
+  PresumedLoc Loc =
+      Context.getSourceManager().getPresumedLoc(Decl->getLocation());
+  DocComment Comment;
+  if (auto *RawComment =
+          getDerivedExtractAPIVisitor().fetchRawCommentForDecl(Decl))
+    Comment = RawComment->getFormattedLines(Context.getSourceManager(),
+                                            Context.getDiagnostics());
+  DeclarationFragments Declaration =
+      DeclarationFragmentsBuilder::getFragmentsForClassTemplateSpecialization(
+          Decl);
+  DeclarationFragments SubHeading =
+      DeclarationFragmentsBuilder::getSubHeading(Decl);
+
+  ClassTemplateSpecRecord *ClassTemplateSpecializationRecord =
+      API.addClassTemplateSpec(Name, USR, Loc, AvailabilitySet(Decl), Comment,
+                               Declaration, SubHeading, isInSystemHeader(Decl));
+
+  // FIXME: store AccessSpecifier given by inheritance
+  for (const auto BaseSpecifier : Decl->bases()) {
+    SymbolReference BaseClass;
+    CXXRecordDecl *BaseClassDecl =
+        BaseSpecifier.getType().getTypePtr()->getAsCXXRecordDecl();
+    BaseClass.Name = BaseClassDecl->getName();
+    BaseClass.USR = API.recordUSR(BaseClassDecl);
+    ClassTemplateSpecializationRecord->Bases.emplace_back(BaseClass);
+  }
+
+  getDerivedExtractAPIVisitor().recordCXXFields(
+      ClassTemplateSpecializationRecord, Decl->fields());
+  getDerivedExtractAPIVisitor().recordCXXMethods(
+      ClassTemplateSpecializationRecord, Decl->methods());
+  return true;
+}
+
+template <typename Derived>
+bool ExtractAPIVisitorBase<Derived>::
+    VisitClassTemplatePartialSpecializationDecl(
+        const ClassTemplatePartialSpecializationDecl *Decl) {
+  if (!getDerivedExtractAPIVisitor().shouldDeclBeIncluded(Decl))
+    return true;
+
+  StringRef Name = Decl->getName();
+  StringRef USR = API.recordUSR(Decl);
+  PresumedLoc Loc =
+      Context.getSourceManager().getPresumedLoc(Decl->getLocation());
+  DocComment Comment;
+  if (auto *RawComment =
+          getDerivedExtractAPIVisitor().fetchRawCommentForDecl(Decl))
+    Comment = RawComment->getFormattedLines(Context.getSourceManager(),
+                                            Context.getDiagnostics());
+  DeclarationFragments Declaration = DeclarationFragmentsBuilder::
+      getFragmentsForClassTemplatePartialSpecialization(Decl);
+  DeclarationFragments SubHeading =
+      DeclarationFragmentsBuilder::getSubHeading(Decl);
+
+  ClassTemplatePartialSpecRecord *ClassTemplatePartialSpecRecord =
+      API.addClassTemplatePartialSpec(
+          Name, USR, Loc, AvailabilitySet(Decl), Comment, Declaration,
+          SubHeading, DeclarationFragmentsBuilder::getTemplate(Decl),
+          isInSystemHeader(Decl));
+
+  // FIXME: store AccessSpecifier given by inheritance
+  for (const auto BaseSpecifier : Decl->bases()) {
+    SymbolReference BaseClass;
+    CXXRecordDecl *BaseClassDecl =
+        BaseSpecifier.getType().getTypePtr()->getAsCXXRecordDecl();
+    BaseClass.Name = BaseClassDecl->getName();
+    BaseClass.USR = API.recordUSR(BaseClassDecl);
+    ClassTemplatePartialSpecRecord->Bases.emplace_back(BaseClass);
+  }
+
+  getDerivedExtractAPIVisitor().recordCXXFields(ClassTemplatePartialSpecRecord,
+                                                Decl->fields());
+  getDerivedExtractAPIVisitor().recordCXXMethods(ClassTemplatePartialSpecRecord,
+                                                 Decl->methods());
+  return true;
+}
+
+template <typename Derived>
 bool ExtractAPIVisitorBase<Derived>::VisitObjCInterfaceDecl(
     const ObjCInterfaceDecl *Decl) {
   if (!getDerivedExtractAPIVisitor().shouldDeclBeIncluded(Decl))
     return true;
 
   // Collect symbol information.
   StringRef Name = Decl->getName();
   StringRef USR = API.recordUSR(Decl);

clang/include/clang/ExtractAPI/Serialization/SerializerBase.h

void traverseAPISet() {
     getDerived()->traverseGlobalFunctionRecords();
 
     getDerived()->traverseEnumRecords();
 
     getDerived()->traverseStaticFieldRecords();
 
     getDerived()->traverseCXXClassRecords();
 
+    getDerived()->traverseClassTemplateRecords();
+
+    getDerived()->traverseClassTemplateSpecRecords();
+
+    getDerived()->traverseClassTemplatePartialSpecRecords();
+
+    getDerived()->traverseConcepts();
+
     getDerived()->traverseStructRecords();
 
     getDerived()->traverseObjCInterfaces();
 
     getDerived()->traverseObjCProtocols();
 
     getDerived()->traverseMacroDefinitionRecords();
 
for (const auto &StaticField : API.getStaticFields())
       getDerived()->visitStaticFieldRecord(*StaticField.second);
   }
 
   void traverseCXXClassRecords() {
     for (const auto &Class : API.getCXXClasses())
       getDerived()->visitCXXClassRecord(*Class.second);
   }
 
+  void traverseClassTemplateRecords() {
+    for (const auto &ClassTemplate : API.getClassTemplates())
+      getDerived()->visitClassTemplateRecord(*ClassTemplate.second);
+  }
+
+  void traverseClassTemplateSpecRecords() {
+    for (const auto &ClassTemplateSpec : API.getClassTemplateSpecializations())
+      getDerived()->visitClassTemplateSpecRecord(*ClassTemplateSpec.second);
+  }
+
+  void traverseClassTemplatePartialSpecRecords() {
+    for (const auto &ClassTemplatePartialSpec :
+         API.getClassTemplatePartialSpecializations())
+      getDerived()->visitClassTemplatePartialSpecRecord(
+          *ClassTemplatePartialSpec.second);
+  }
+
+  void traverseConcepts() {
+    for (const auto &Concept : API.getConcepts())
+      getDerived()->visitConceptRecord(*Concept.second);
+  }
+
   void traverseObjCInterfaces() {
     for (const auto &Interface : API.getObjCInterfaces())
       getDerived()->visitObjCContainerRecord(*Interface.second);
   }
 
   void traverseObjCProtocols() {
     for (const auto &Protocol : API.getObjCProtocols())
       getDerived()->visitObjCContainerRecord(*Protocol.second);
public:
 
   /// Visit a struct record.
   void visitStructRecord(const StructRecord &Record){};
 
   void visitStaticFieldRecord(const StaticFieldRecord &Record){};
 
   void visitCXXClassRecord(const CXXClassRecord &Record){};
 
+  void visitClassTemplateRecord(const ClassTemplateRecord &Record){};
+
   /// Visit an Objective-C container record.
   void visitObjCContainerRecord(const ObjCContainerRecord &Record){};
 
   /// Visit a macro definition record.
   void visitMacroDefinitionRecord(const MacroDefinitionRecord &Record){};
 
   /// Visit a typedef record.
   void visitTypedefRecord(const TypedefRecord &Record){};

clang/include/clang/ExtractAPI/Serialization/SymbolGraphSerializer.h

enum RelationshipKind {
     /// The source symbol conforms to the target symbol.
     /// For example Objective-C protocol conformances.
     ConformsTo,
   };
 
   /// Get the string representation of the relationship kind.
   static StringRef getRelationshipString(RelationshipKind Kind);
 
+  enum ConstraintKind { Conformance, ConditionalConformance };
+
+  static StringRef getConstraintString(ConstraintKind Kind);
+
 private:
   /// Just serialize the currently recorded objects in Symbol Graph format.
   Object serializeCurrentGraph();
 
   /// Synthesize the metadata section of the Symbol Graph format.
   ///
   /// The metadata section describes information about the Symbol Graph itself,
   /// including the format version and the generator information.
public:
 
   /// Visit a struct record.
   void visitStructRecord(const StructRecord &Record);
 
   void visitStaticFieldRecord(const StaticFieldRecord &Record);
 
   void visitCXXClassRecord(const CXXClassRecord &Record);
 
+  void visitClassTemplateRecord(const ClassTemplateRecord &Record);
+
+  void visitClassTemplateSpecRecord(const ClassTemplateSpecRecord &Record);
+
+  void visitClassTemplatePartialSpecRecord(
+      const ClassTemplatePartialSpecRecord &Record);
+
+  void visitConceptRecord(const ConceptRecord &Record);
+
   /// Visit an Objective-C container record.
   void visitObjCContainerRecord(const ObjCContainerRecord &Record);
 
   /// Visit a macro definition record.
   void visitMacroDefinitionRecord(const MacroDefinitionRecord &Record);
 
   /// Visit a typedef record.
   void visitTypedefRecord(const TypedefRecord &Record);

clang/lib/ExtractAPI/API.cpp

APISet::addCXXClass(StringRef Name, StringRef USR, PresumedLoc Loc,
                     DeclarationFragments Declaration,
                     DeclarationFragments SubHeading, APIRecord::RecordKind Kind,
                     bool IsFromSystemHeader) {
   return addTopLevelRecord(USRBasedLookupTable, CXXClasses, USR, Name, Loc,
                            std::move(Availabilities), Comment, Declaration,
                            SubHeading, Kind, IsFromSystemHeader);
 }
 
+ClassTemplateRecord *APISet::addClassTemplate(
+    StringRef Name, StringRef USR, PresumedLoc Loc,
+    AvailabilitySet Availability, const DocComment &Comment,
+    DeclarationFragments Declaration, DeclarationFragments SubHeading,
+    Template Template, bool IsFromSystemHeader) {
+
+  return addTopLevelRecord(USRBasedLookupTable, ClassTemplates, USR, Name, Loc,
+                           std::move(Availability), Comment, Declaration,
+                           SubHeading, Template, IsFromSystemHeader);
+}
+
+ClassTemplateSpecRecord *APISet::addClassTemplateSpec(
+    StringRef Name, StringRef USR, PresumedLoc Loc,
+    AvailabilitySet Availability, const DocComment &Comment,
+    DeclarationFragments Declaration, DeclarationFragments SubHeading,
+    bool IsFromSystemHeader) {
+  return addTopLevelRecord(USRBasedLookupTable, ClassTemplateSpecializations,
+                           USR, Name, Loc, std::move(Availability), Comment,
+                           Declaration, SubHeading, IsFromSystemHeader);
+}
+
+ClassTemplatePartialSpecRecord *APISet::addClassTemplatePartialSpec(
+    StringRef Name, StringRef USR, PresumedLoc Loc,
+    AvailabilitySet Availability, const DocComment &Comment,
+    DeclarationFragments Declaration, DeclarationFragments SubHeading,
+    Template Template, bool IsFromSystemHeader) {
+  return addTopLevelRecord(USRBasedLookupTable,
+                           ClassTemplatePartialSpecializations, USR, Name, Loc,
+                           std::move(Availability), Comment, Declaration,
+                           SubHeading, Template, IsFromSystemHeader);
+}
+
+ConceptRecord *APISet::addConcept(StringRef Name, StringRef USR,
+                                  PresumedLoc Loc, AvailabilitySet Availability,
+                                  const DocComment &Comment,
+                                  DeclarationFragments Declaration,
+                                  DeclarationFragments SubHeading,
+                                  Template Template, bool IsFromSystemHeader) {
+  return addTopLevelRecord(USRBasedLookupTable, Concepts, USR, Name, Loc,
+                           std::move(Availability), Comment, Declaration,
+                           SubHeading, Template, IsFromSystemHeader);
+}
+
 CXXMethodRecord *APISet::addCXXMethod(
     CXXClassRecord *CXXClassRecord, StringRef Name, StringRef USR,
     PresumedLoc Loc, AvailabilitySet Availability, const DocComment &Comment,
     DeclarationFragments Declaration, DeclarationFragments SubHeading,
     FunctionSignature Signature, bool IsStatic, AccessControl Access,
     bool IsFromSystemHeader) {
   std::unique_ptr<CXXMethodRecord> Record;
   if (IsStatic)

clang/lib/ExtractAPI/DeclarationFragments.cpp

DeclarationFragmentsBuilder::getFragmentsForOverloadedOperator(
 
   Fragments.append(DeclarationFragments::getExceptionSpecificationString(
       Method->getExceptionSpecType()));
 
   return Fragments.append(";", DeclarationFragments::FragmentKind::Text);
 }
 
 DeclarationFragments
+DeclarationFragmentsBuilder::getFragmentsForTemplateParameters(
+    ArrayRef<NamedDecl *> ParameterArray) {
+  DeclarationFragments Fragments;
+  for (unsigned i = 0, end = ParameterArray.size(); i != end; ++i) {
+    if (i)
+      Fragments.append(",", DeclarationFragments::FragmentKind::Text)
+          .appendSpace();
+
+    const auto *TemplateParam =
+        dyn_cast<TemplateTypeParmDecl>(ParameterArray[i]);
+    if (!TemplateParam)
+      continue;
+    if (TemplateParam->hasTypeConstraint())
+      Fragments.append(TemplateParam->getTypeConstraint()
+                           ->getNamedConcept()
+                           ->getName()
+                           .str(),
+                       DeclarationFragments::FragmentKind::TypeIdentifier);
+    else if (TemplateParam->wasDeclaredWithTypename())
+      Fragments.append("typename", DeclarationFragments::FragmentKind::Keyword);
+    else
+      Fragments.append("class", DeclarationFragments::FragmentKind::Keyword);
+
+    if (TemplateParam->isParameterPack())
+      Fragments.append("...", DeclarationFragments::FragmentKind::Text);
+
+    Fragments.appendSpace().append(
+        TemplateParam->getName(),
+        DeclarationFragments::FragmentKind::GenericParameter);
+  }
+  return Fragments;
+}
+
+DeclarationFragments
+DeclarationFragmentsBuilder::getFragmentsForTemplateArguments(
+    const ArrayRef<TemplateArgument> TemplateArguments,
+    const std::optional<ArrayRef<NamedDecl *>> TemplateParameters) {
+  DeclarationFragments Fragments;
+  for (unsigned i = 0, end = TemplateArguments.size(); i != end; ++i) {
+    if (i)
+      Fragments.append(",", DeclarationFragments::FragmentKind::Text)
+          .appendSpace();
+
+    std::string Type = TemplateArguments[i].getAsType().getAsString();
+    std::string Name;
+    std::string ex = Type.substr(0, 14);
+    if (Type.substr(0, 14).compare("type-parameter") == 0) {
+      // The arg is a template parameter from a partial spec.
+      if (TemplateParameters)
+        for (unsigned j = 0; j < TemplateParameters->size(); ++j) {
+          const auto *Parameter =
+              dyn_cast<TemplateTypeParmDecl>((*TemplateParameters)[j]);
+          if (Type.compare("type-parameter-" +
+                           std::to_string(Parameter->getIndex()) +
+                           std::to_string(Parameter->getDepth())))
+            Name = (*TemplateParameters)[j]->getName();
+        }
+    } else
+      Name = Type;
+
+    Fragments.append(Name, DeclarationFragments::FragmentKind::TypeIdentifier);
+    if (TemplateArguments[i].isPackExpansion())
+      Fragments.append("...", DeclarationFragments::FragmentKind::Text);
+  }
+  return Fragments;
+}
+
+DeclarationFragments DeclarationFragmentsBuilder::getFragmentsForConcept(
+    const ConceptDecl *Concept) {
+  DeclarationFragments Fragments;
+  return Fragments
+      .append("template", DeclarationFragments::FragmentKind::Keyword)
+      .append("<", DeclarationFragments::FragmentKind::Text)
+      .append(getFragmentsForTemplateParameters(
+          Concept->getTemplateParameters()->asArray()))
+      .append("> ", DeclarationFragments::FragmentKind::Text)
+      .append("concept", DeclarationFragments::FragmentKind::Keyword)
+      .appendSpace()
+      .append(Concept->getName().str(),
+              DeclarationFragments::FragmentKind::Identifier)
+      .append(";", DeclarationFragments::FragmentKind::Text);
+}
+
+DeclarationFragments
+DeclarationFragmentsBuilder::getFragmentsForRedeclarableTemplate(
+    const RedeclarableTemplateDecl *RedeclarableTemplate) {
+  DeclarationFragments Fragments;
+  Fragments.append("template", DeclarationFragments::FragmentKind::Keyword)
+      .append("<", DeclarationFragments::FragmentKind::Text)
+      .append(getFragmentsForTemplateParameters(
+          RedeclarableTemplate->getTemplateParameters()->asArray()))
+      .append(">", DeclarationFragments::FragmentKind::Text)
+      .appendSpace();
+
+  if (isa<TypeAliasTemplateDecl>(RedeclarableTemplate))
+    Fragments.appendSpace()
+        .append("using", DeclarationFragments::FragmentKind::Keyword)
+        .appendSpace()
+        .append(RedeclarableTemplate->getName(),
+                DeclarationFragments::FragmentKind::Identifier);
+  // the templated records will be resposbible for injecting their templates
+  return Fragments.appendSpace();
+}
+
+DeclarationFragments
+DeclarationFragmentsBuilder::getFragmentsForClassTemplateSpecialization(
+    const ClassTemplateSpecializationDecl *Decl) {
+  DeclarationFragments Fragments;
+  return Fragments
+      .append("template", DeclarationFragments::FragmentKind::Keyword)
+      .append("<", DeclarationFragments::FragmentKind::Text)
+      .append(">", DeclarationFragments::FragmentKind::Text)
+      .appendSpace()
+      .append(DeclarationFragmentsBuilder::getFragmentsForCXXClass(
+          cast<CXXRecordDecl>(Decl)))
+      .pop_back() // there is an extra semicolon now
+      .append("<", DeclarationFragments::FragmentKind::Text)
+      .append(getFragmentsForTemplateArguments(
+          Decl->getTemplateArgs().asArray(), std::nullopt))
+      .append(">", DeclarationFragments::FragmentKind::Text)
+      .append(";", DeclarationFragments::FragmentKind::Text);
+}
+
+DeclarationFragments
+DeclarationFragmentsBuilder::getFragmentsForClassTemplatePartialSpecialization(
+    const ClassTemplatePartialSpecializationDecl *Decl) {
+  DeclarationFragments Fragments;
+  return Fragments
+      .append("template", DeclarationFragments::FragmentKind::Keyword)
+      .append("<", DeclarationFragments::FragmentKind::Text)
+      .append(getFragmentsForTemplateParameters(
+          Decl->getTemplateParameters()->asArray()))
+      .append(">", DeclarationFragments::FragmentKind::Text)
+      .appendSpace()
+      .append(DeclarationFragmentsBuilder::getFragmentsForCXXClass(
+          cast<CXXRecordDecl>(Decl)))
+      .pop_back() // there is an extra semicolon now
+      .append("<", DeclarationFragments::FragmentKind::Text)
+      .append(getFragmentsForTemplateArguments(
+          Decl->getTemplateArgs().asArray(),
+          Decl->getTemplateParameters()->asArray()))
+      .append(">", DeclarationFragments::FragmentKind::Text)
+      .append(";", DeclarationFragments::FragmentKind::Text);
+}
+
+DeclarationFragments
 DeclarationFragmentsBuilder::getFragmentsForMacro(StringRef Name,
                                                   const MacroDirective *MD) {
   DeclarationFragments Fragments;
   Fragments.append("#define", DeclarationFragments::FragmentKind::Keyword)
       .appendSpace();
   Fragments.append(Name, DeclarationFragments::FragmentKind::Identifier);
 
   auto *MI = MD->getMacroInfo();

clang/lib/ExtractAPI/Serialization/SymbolGraphSerializer.cpp

Object serializeSymbolKind(APIRecord::RecordKind RK, Language Lang) {
   case APIRecord::RK_Union:
     Kind["identifier"] = AddLangPrefix("union");
     Kind["displayName"] = "Union";
     break;
   case APIRecord::RK_StaticField:
     Kind["identifier"] = AddLangPrefix("type.property");
     Kind["displayName"] = "Type Property";
     break;
+  case APIRecord::RK_ClassTemplate:
+  case APIRecord::RK_ClassTemplateSpecialization:
+  case APIRecord::RK_ClassTemplatePartialSpecialization:
   case APIRecord::RK_CXXClass:
     Kind["identifier"] = AddLangPrefix("class");
     Kind["displayName"] = "Class";
     break;
+  case APIRecord::RK_Concept:
+    Kind["identifier"] = AddLangPrefix("concept");
+    Kind["displayName"] = "Concept";
+    break;
   case APIRecord::RK_CXXStaticMethod:
     Kind["identifier"] = AddLangPrefix("type.method");
     Kind["displayName"] = "Static Method";
     break;
   case APIRecord::RK_CXXInstanceMethod:
     Kind["identifier"] = AddLangPrefix("method");
     Kind["displayName"] = "Instance Method";
     break;

 template <typename RecordTy>
 void serializeAccessMixin(Object &Paren, const RecordTy &Record) {
   auto accessLevel = serializeAccessMixinImpl(Record, has_access<RecordTy>());
   if (!accessLevel.has_value())
     accessLevel = "public";
   serializeString(Paren, "accessLevel", accessLevel);
 }
 
+template <typename RecordTy>
+std::optional<Object> serializeTemplateMixinImpl(const RecordTy &Record,
+                                                 std::true_type) {
+  const auto &Template = Record.Templ;
+  if (Template.empty())
+    return std::nullopt;
+
+  Object Generics;
+  Array GenericParameters;
+  for (const auto Param : Template.getParameters()) {
+    Object Parameter;
+    Parameter["name"] = Param.Name;
+    Parameter["index"] = Param.Index;
+    Parameter["depth"] = Param.Depth;
+    GenericParameters.emplace_back(std::move(Parameter));
+  }
+  if (!GenericParameters.empty())
+    Generics["parameters"] = std::move(GenericParameters);
+
+  Array GenericConstraints;
+  for (const auto Constr : Template.getConstraints()) {
+    Object Constraint;
+    Constraint["kind"] = Constr.Kind;
+    Constraint["lhs"] = Constr.LHS;
+    Constraint["rhs"] = Constr.RHS;
+    GenericConstraints.emplace_back(std::move(Constraint));
+  }
+
+  if (!GenericConstraints.empty())
+    Generics["constraints"] = std::move(GenericConstraints);
+
+  return Generics;
+}
+
+template <typename RecordTy>
+std::optional<Object> serializeTemplateMixinImpl(const RecordTy &Record,
+                                                 std::false_type) {
+  return std::nullopt;
+}
+
+template <typename RecordTy>
+void serializeTemplateMixin(Object &Paren, const RecordTy &Record) {
+  serializeObject(Paren, "swiftGenerics",
+                  serializeTemplateMixinImpl(Record, has_template<RecordTy>()));
+}
+
 struct PathComponent {
   StringRef USR;
   StringRef Name;
   APIRecord::RecordKind Kind;
 
   PathComponent(StringRef USR, StringRef Name, APIRecord::RecordKind Kind)
       : USR(USR), Name(Name), Kind(Kind) {}
 };
if (generatePathComponents(Record, API,
                                PathComponentsNames.push_back(PC.Name);
                              }))
     return {};
 
   serializeArray(Obj, "pathComponents", Array(PathComponentsNames));
 
   serializeFunctionSignatureMixin(Obj, Record);
   serializeAccessMixin(Obj, Record);
+  serializeTemplateMixin(Obj, Record);
 
   return Obj;
 }
 
 template <typename MemberTy>
 void SymbolGraphSerializer::serializeMembers(
     const APIRecord &Record,
     const SmallVector<std::unique_ptr<MemberTy>> &Members) {
StringRef SymbolGraphSerializer::getRelationshipString(RelationshipKind Kind) {
   case RelationshipKind::InheritsFrom:
     return "inheritsFrom";
   case RelationshipKind::ConformsTo:
     return "conformsTo";
   }
   llvm_unreachable("Unhandled relationship kind");
 }
 
+StringRef SymbolGraphSerializer::getConstraintString(ConstraintKind Kind) {
+  switch (Kind) {
+  case ConstraintKind::Conformance:
+    return "conformance";
+  case ConstraintKind::ConditionalConformance:
+    return "conditionalConformance";
+  }
+  llvm_unreachable("Unhandled constraint kind");
+}
+
 void SymbolGraphSerializer::serializeRelationship(RelationshipKind Kind,
                                                   SymbolReference Source,
                                                   SymbolReference Target) {
   Object Relationship;
   Relationship["source"] = Source.USR;
   Relationship["target"] = Target.USR;
   Relationship["targetFallback"] = Target.Name;
   Relationship["kind"] = getRelationshipString(Kind);
void SymbolGraphSerializer::visitCXXClassRecord(const CXXClassRecord &Record) {
   Symbols.emplace_back(std::move(*Class));
   serializeMembers(Record, Record.Fields);
   serializeMembers(Record, Record.Methods);
 
   for (const auto Base : Record.Bases)
     serializeRelationship(RelationshipKind::InheritsFrom, Record, Base);
 }
 
+void SymbolGraphSerializer::visitClassTemplateRecord(
+    const ClassTemplateRecord &Record) {
+  auto Class = serializeAPIRecord(Record);
+  if (!Class)
+    return;
+
+  Symbols.emplace_back(std::move(*Class));
+  serializeMembers(Record, Record.Fields);
+  serializeMembers(Record, Record.Methods);
+
+  for (const auto Base : Record.Bases)
+    serializeRelationship(RelationshipKind::InheritsFrom, Record, Base);
+}
+
+void SymbolGraphSerializer::visitClassTemplateSpecRecord(
+    const ClassTemplateSpecRecord &Record) {
+  auto Class = serializeAPIRecord(Record);
+  if (!Class)
+    return;
+
+  Symbols.emplace_back(std::move(*Class));
+  serializeMembers(Record, Record.Fields);
+  serializeMembers(Record, Record.Methods);
+
+  for (const auto Base : Record.Bases)
+    serializeRelationship(RelationshipKind::InheritsFrom, Record, Base);
+}
+
+void SymbolGraphSerializer::visitClassTemplatePartialSpecRecord(
+    const ClassTemplatePartialSpecRecord &Record) {
+  auto Class = serializeAPIRecord(Record);
+  if (!Class)
+    return;
+
+  Symbols.emplace_back(std::move(*Class));
+  serializeMembers(Record, Record.Fields);
+  serializeMembers(Record, Record.Methods);
+
+  for (const auto Base : Record.Bases)
+    serializeRelationship(RelationshipKind::InheritsFrom, Record, Base);
+}
+
+void SymbolGraphSerializer::visitConceptRecord(const ConceptRecord &Record) {
+  auto Concept = serializeAPIRecord(Record);
+  if (!Concept)
+    return;
+
+  Symbols.emplace_back(std::move(*Concept));
+}
+
 void SymbolGraphSerializer::visitObjCContainerRecord(
     const ObjCContainerRecord &Record) {
   auto ObjCContainer = serializeAPIRecord(Record);
   if (!ObjCContainer)
     return;
 
   Symbols.emplace_back(std::move(*ObjCContainer));
 

clang/test/ExtractAPI/class_template.cpp

+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed -e "s@INPUT_DIR@%{/t:regex_replacement}@g" \
+// RUN: %t/reference.output.json.in >> %t/reference.output.json
+// RUN: %clang_cc1 -extract-api -triple arm64-apple-macosx \
+// RUN:   -x c++-header %t/input.h -o %t/output.json -verify
+
+// Generator version is not consistent across test runs, normalize it.
+// RUN: sed -e "s@\"generator\": \".*\"@\"generator\": \"?\"@g" \
+// RUN: %t/output.json >> %t/output-normalized.json
+// RUN: diff %t/reference.output.json %t/output-normalized.json
+
+//--- input.h
+template<typename T> class Foo {};
+
+/// expected-no-diagnostics
+
+//--- reference.output.json.in
+{
+  "metadata": {
+    "formatVersion": {
+      "major": 0,
+      "minor": 5,
+      "patch": 3
+    },
+    "generator": "?"
+  },
+  "module": {
+    "name": "",
+    "platform": {
+      "architecture": "arm64",
+      "operatingSystem": {
+        "minimumVersion": {
+          "major": 11,
+          "minor": 0,
+          "patch": 0
+        },
+        "name": "macosx"
+      },
+      "vendor": "apple"
+    }
+  },
+  "relationships": [],
+  "symbols": [
+    {
+      "accessLevel": "public",
+      "declarationFragments": [
+        {
+          "kind": "keyword",
+          "spelling": "template"
+        },
+        {
+          "kind": "text",
+          "spelling": "<"
+        },
+        {
+          "kind": "keyword",
+          "spelling": "typename"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "genericParameter",
+          "spelling": "T"
+        },
+        {
+          "kind": "text",
+          "spelling": "> "
+        },
+        {
+          "kind": "keyword",
+          "spelling": "class"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "identifier",
+          "spelling": "Foo"
+        },
+        {
+          "kind": "text",
+          "spelling": ";"
+        }
+      ],
+      "identifier": {
+        "interfaceLanguage": "c++",
+        "precise": "c:@ST>1#T@Foo"
+      },
+      "kind": {
+        "displayName": "Class",
+        "identifier": "c++.class"
+      },
+      "location": {
+        "position": {
+          "character": 28,
+          "line": 1
+        },
+        "uri": "file://INPUT_DIR/input.h"
+      },
+      "names": {
+        "navigator": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "subHeading": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "title": "Foo"
+      },
+      "pathComponents": [
+        "Foo"
+      ],
+      "swiftGenerics": {
+        "parameters": [
+          {
+            "depth": 0,
+            "index": 0,
+            "name": "T"
+          }
+        ]
+      }
+    }
+  ]
+}

clang/test/ExtractAPI/class_template_partial_spec.cpp

+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed -e "s@INPUT_DIR@%{/t:regex_replacement}@g" \
+// RUN: %t/reference.output.json.in >> %t/reference.output.json
+// RUN: %clang_cc1 -extract-api -triple arm64-apple-macosx \
+// RUN:   -x c++-header %t/input.h -o %t/output.json -verify
+
+// Generator version is not consistent across test runs, normalize it.
+// RUN: sed -e "s@\"generator\": \".*\"@\"generator\": \"?\"@g" \
+// RUN: %t/output.json >> %t/output-normalized.json
+// RUN: diff %t/reference.output.json %t/output-normalized.json
+
+//--- input.h
+template<typename X, typename Y> class Foo {};
+
+template<typename Z> class Foo<Z, int> {};
+
+/// expected-no-diagnostics
+
+//--- reference.output.json.in
+{
+  "metadata": {
+    "formatVersion": {
+      "major": 0,
+      "minor": 5,
+      "patch": 3
+    },
+    "generator": "?"
+  },
+  "module": {
+    "name": "",
+    "platform": {
+      "architecture": "arm64",
+      "operatingSystem": {
+        "minimumVersion": {
+          "major": 11,
+          "minor": 0,
+          "patch": 0
+        },
+        "name": "macosx"
+      },
+      "vendor": "apple"
+    }
+  },
+  "relationships": [],
+  "symbols": [
+    {
+      "accessLevel": "public",
+      "declarationFragments": [
+        {
+          "kind": "keyword",
+          "spelling": "template"
+        },
+        {
+          "kind": "text",
+          "spelling": "<"
+        },
+        {
+          "kind": "keyword",
+          "spelling": "typename"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "genericParameter",
+          "spelling": "X"
+        },
+        {
+          "kind": "text",
+          "spelling": ", "
+        },
+        {
+          "kind": "keyword",
+          "spelling": "typename"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "genericParameter",
+          "spelling": "Y"
+        },
+        {
+          "kind": "text",
+          "spelling": "> "
+        },
+        {
+          "kind": "keyword",
+          "spelling": "class"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "identifier",
+          "spelling": "Foo"
+        },
+        {
+          "kind": "text",
+          "spelling": ";"
+        }
+      ],
+      "identifier": {
+        "interfaceLanguage": "c++",
+        "precise": "c:@ST>2#T#T@Foo"
+      },
+      "kind": {
+        "displayName": "Class",
+        "identifier": "c++.class"
+      },
+      "location": {
+        "position": {
+          "character": 40,
+          "line": 1
+        },
+        "uri": "file://INPUT_DIR/input.h"
+      },
+      "names": {
+        "navigator": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "subHeading": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "title": "Foo"
+      },
+      "pathComponents": [
+        "Foo"
+      ],
+      "swiftGenerics": {
+        "parameters": [
+          {
+            "depth": 0,
+            "index": 0,
+            "name": "X"
+          },
+          {
+            "depth": 0,
+            "index": 1,
+            "name": "Y"
+          }
+        ]
+      }
+    },
+    {
+      "accessLevel": "public",
+      "declarationFragments": [
+        {
+          "kind": "keyword",
+          "spelling": "template"
+        },
+        {
+          "kind": "text",
+          "spelling": "<"
+        },
+        {
+          "kind": "keyword",
+          "spelling": "typename"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "genericParameter",
+          "spelling": "Z"
+        },
+        {
+          "kind": "text",
+          "spelling": "> "
+        },
+        {
+          "kind": "keyword",
+          "spelling": "class"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "identifier",
+          "spelling": "Foo"
+        },
+        {
+          "kind": "text",
+          "spelling": "<"
+        },
+        {
+          "kind": "typeIdentifier",
+          "spelling": "Z"
+        },
+        {
+          "kind": "text",
+          "spelling": ", "
+        },
+        {
+          "kind": "typeIdentifier",
+          "spelling": "int"
+        },
+        {
+          "kind": "text",
+          "spelling": ">;"
+        }
+      ],
+      "identifier": {
+        "interfaceLanguage": "c++",
+        "precise": "c:@SP>1#T@Foo>#t0.0#I"
+      },
+      "kind": {
+        "displayName": "Class",
+        "identifier": "c++.class"
+      },
+      "location": {
+        "position": {
+          "character": 28,
+          "line": 3
+        },
+        "uri": "file://INPUT_DIR/input.h"
+      },
+      "names": {
+        "navigator": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "subHeading": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "title": "Foo"
+      },
+      "pathComponents": [
+        "Foo"
+      ],
+      "swiftGenerics": {
+        "parameters": [
+          {
+            "depth": 0,
+            "index": 0,
+            "name": "Z"
+          }
+        ]
+      }
+    }
+  ]
+}

clang/test/ExtractAPI/class_template_spec.cpp

+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed -e "s@INPUT_DIR@%{/t:regex_replacement}@g" \
+// RUN: %t/reference.output.json.in >> %t/reference.output.json
+// RUN: %clang_cc1 -extract-api -triple arm64-apple-macosx \
+// RUN:   -x c++-header %t/input.h -o %t/output.json -verify
+
+// Generator version is not consistent across test runs, normalize it.
+// RUN: sed -e "s@\"generator\": \".*\"@\"generator\": \"?\"@g" \
+// RUN: %t/output.json >> %t/output-normalized.json
+// RUN: diff %t/reference.output.json %t/output-normalized.json
+
+//--- input.h
+template<typename T> class Foo {};
+
+template<> class Foo<int> {};
+
+/// expected-no-diagnostics
+
+//--- reference.output.json.in
+{
+  "metadata": {
+    "formatVersion": {
+      "major": 0,
+      "minor": 5,
+      "patch": 3
+    },
+    "generator": "?"
+  },
+  "module": {
+    "name": "",
+    "platform": {
+      "architecture": "arm64",
+      "operatingSystem": {
+        "minimumVersion": {
+          "major": 11,
+          "minor": 0,
+          "patch": 0
+        },
+        "name": "macosx"
+      },
+      "vendor": "apple"
+    }
+  },
+  "relationships": [],
+  "symbols": [
+    {
+      "accessLevel": "public",
+      "declarationFragments": [
+        {
+          "kind": "keyword",
+          "spelling": "template"
+        },
+        {
+          "kind": "text",
+          "spelling": "<"
+        },
+        {
+          "kind": "keyword",
+          "spelling": "typename"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "genericParameter",
+          "spelling": "T"
+        },
+        {
+          "kind": "text",
+          "spelling": "> "
+        },
+        {
+          "kind": "keyword",
+          "spelling": "class"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "identifier",
+          "spelling": "Foo"
+        },
+        {
+          "kind": "text",
+          "spelling": ";"
+        }
+      ],
+      "identifier": {
+        "interfaceLanguage": "c++",
+        "precise": "c:@ST>1#T@Foo"
+      },
+      "kind": {
+        "displayName": "Class",
+        "identifier": "c++.class"
+      },
+      "location": {
+        "position": {
+          "character": 28,
+          "line": 1
+        },
+        "uri": "file://INPUT_DIR/input.h"
+      },
+      "names": {
+        "navigator": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "subHeading": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "title": "Foo"
+      },
+      "pathComponents": [
+        "Foo"
+      ],
+      "swiftGenerics": {
+        "parameters": [
+          {
+            "depth": 0,
+            "index": 0,
+            "name": "T"
+          }
+        ]
+      }
+    },
+    {
+      "accessLevel": "public",
+      "declarationFragments": [
+        {
+          "kind": "keyword",
+          "spelling": "template"
+        },
+        {
+          "kind": "text",
+          "spelling": "<> "
+        },
+        {
+          "kind": "keyword",
+          "spelling": "class"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "identifier",
+          "spelling": "Foo"
+        },
+        {
+          "kind": "text",
+          "spelling": "<"
+        },
+        {
+          "kind": "typeIdentifier",
+          "spelling": "int"
+        },
+        {
+          "kind": "text",
+          "spelling": ">;"
+        }
+      ],
+      "identifier": {
+        "interfaceLanguage": "c++",
+        "precise": "c:@S@Foo>#I"
+      },
+      "kind": {
+        "displayName": "Class",
+        "identifier": "c++.class"
+      },
+      "location": {
+        "position": {
+          "character": 18,
+          "line": 3
+        },
+        "uri": "file://INPUT_DIR/input.h"
+      },
+      "names": {
+        "navigator": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "subHeading": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "title": "Foo"
+      },
+      "pathComponents": [
+        "Foo"
+      ]
+    }
+  ]
+}

clang/test/ExtractAPI/concept.cpp

+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed -e "s@INPUT_DIR@%{/t:regex_replacement}@g" \
+// RUN: %t/reference.output.json.in >> %t/reference.output.json
+// RUN: %clang_cc1 -std=c++20 -extract-api -triple arm64-apple-macosx \
+// RUN:   -x c++-header %t/input.h -o %t/output.json -verify
+
+// Generator version is not consistent across test runs, normalize it.
+// RUN: sed -e "s@\"generator\": \".*\"@\"generator\": \"?\"@g" \
+// RUN: %t/output.json >> %t/output-normalized.json
+// RUN: diff %t/reference.output.json %t/output-normalized.json
+
+//--- input.h
+template<typename T> concept Foo = true;
+
+/// expected-no-diagnostics
+
+//--- reference.output.json.in
+{
+  "metadata": {
+    "formatVersion": {
+      "major": 0,
+      "minor": 5,
+      "patch": 3
+    },
+    "generator": "?"
+  },
+  "module": {
+    "name": "",
+    "platform": {
+      "architecture": "arm64",
+      "operatingSystem": {
+        "minimumVersion": {
+          "major": 11,
+          "minor": 0,
+          "patch": 0
+        },
+        "name": "macosx"
+      },
+      "vendor": "apple"
+    }
+  },
+  "relationships": [],
+  "symbols": [
+    {
+      "accessLevel": "public",
+      "declarationFragments": [
+        {
+          "kind": "keyword",
+          "spelling": "template"
+        },
+        {
+          "kind": "text",
+          "spelling": "<"
+        },
+        {
+          "kind": "keyword",
+          "spelling": "typename"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "genericParameter",
+          "spelling": "T"
+        },
+        {
+          "kind": "text",
+          "spelling": "> "
+        },
+        {
+          "kind": "keyword",
+          "spelling": "concept"
+        },
+        {
+          "kind": "text",
+          "spelling": " "
+        },
+        {
+          "kind": "identifier",
+          "spelling": "Foo"
+        },
+        {
+          "kind": "text",
+          "spelling": ";"
+        }
+      ],
+      "identifier": {
+        "interfaceLanguage": "c++",
+        "precise": "c:@CT@Foo"
+      },
+      "kind": {
+        "displayName": "Concept",
+        "identifier": "c++.concept"
+      },
+      "location": {
+        "position": {
+          "character": 30,
+          "line": 1
+        },
+        "uri": "file://INPUT_DIR/input.h"
+      },
+      "names": {
+        "navigator": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "subHeading": [
+          {
+            "kind": "identifier",
+            "spelling": "Foo"
+          }
+        ],
+        "title": "Foo"
+      },
+      "pathComponents": [
+        "Foo"
+      ],
+      "swiftGenerics": {
+        "parameters": [
+          {
+            "depth": 0,
+            "index": 0,
+            "name": "T"
+          }
+        ]
+      }
+    }
+  ]
+}