[Concepts] Concept definitions (D40381)

First in a series of patches to land C++2a Concepts support.
This patch adds AST and parsing support for concept-declarations.

llvm-svn: 365699

clang/include/clang/AST/ASTNodeTraverser.h

@@ -529,6 +529,11 @@ class ASTNodeTraverser
           D->defaultArgumentWasInherited() ? "inherited from" : "previous");
   }
 
+  void VisitConceptDecl(const ConceptDecl *D) {
+    dumpTemplateParameters(D->getTemplateParameters());
+    Visit(D->getConstraintExpr());
+  }
+
   void VisitUsingShadowDecl(const UsingShadowDecl *D) {
     if (auto *TD = dyn_cast<TypeDecl>(D->getUnderlyingDecl()))
       Visit(TD->getTypeForDecl());

clang/include/clang/AST/DeclTemplate.h

@@ -3090,6 +3090,42 @@ class VarTemplateDecl : public RedeclarableTemplateDecl {
   static bool classofKind(Kind K) { return K == VarTemplate; }
 };
 
+// \brief Declaration of a C++2a concept.
+class ConceptDecl : public TemplateDecl, public Mergeable<ConceptDecl> {
+protected:
+  Expr *ConstraintExpr;
+
+  ConceptDecl(DeclContext *DC,
+              SourceLocation L, DeclarationName Name,
+              TemplateParameterList *Params,
+              Expr *ConstraintExpr)
+      : TemplateDecl(nullptr, Concept, DC, L, Name, Params),
+        ConstraintExpr(ConstraintExpr) {};
+public:
+  static ConceptDecl *Create(ASTContext &C, DeclContext *DC,
+                             SourceLocation L, DeclarationName Name,
+                             TemplateParameterList *Params,
+                             Expr *ConstraintExpr);
+  static ConceptDecl *CreateDeserialized(ASTContext &C, unsigned ID);
+
+  Expr *getConstraintExpr() const {
+    return ConstraintExpr;
+  }
+
+  SourceRange getSourceRange() const override LLVM_READONLY {
+    return SourceRange(getTemplateParameters()->getTemplateLoc(),
+                       ConstraintExpr->getEndLoc());
+  }
+
+  // Implement isa/cast/dyncast/etc.
+  static bool classof(const Decl *D) { return classofKind(D->getKind()); }
+  static bool classofKind(Kind K) { return K == Concept; }
+
+  friend class ASTReader;
+  friend class ASTDeclReader;
+  friend class ASTDeclWriter;
+};
+
 inline NamedDecl *getAsNamedDecl(TemplateParameter P) {
   if (auto *PD = P.dyn_cast<TemplateTypeParmDecl *>())
     return PD;

clang/include/clang/AST/RecursiveASTVisitor.h

@@ -1800,6 +1800,11 @@ DEF_TRAVERSE_DECL(TypeAliasTemplateDecl, {
   TRY_TO(TraverseTemplateParameterListHelper(D->getTemplateParameters()));
 })
 
+DEF_TRAVERSE_DECL(ConceptDecl, {
+  TRY_TO(TraverseTemplateParameterListHelper(D->getTemplateParameters()));
+  TRY_TO(TraverseStmt(D->getConstraintExpr()));
+})
+
 DEF_TRAVERSE_DECL(UnresolvedUsingTypenameDecl, {
   // A dependent using declaration which was marked with 'typename'.
   //   template<class T> class A : public B<T> { using typename B<T>::foo; };

clang/include/clang/AST/TextNodeDumper.h

@@ -347,6 +347,7 @@ class TextNodeDumper
   void VisitObjCPropertyDecl(const ObjCPropertyDecl *D);
   void VisitObjCPropertyImplDecl(const ObjCPropertyImplDecl *D);
   void VisitBlockDecl(const BlockDecl *D);
+  void VisitConceptDecl(const ConceptDecl *D);
 };
 
 } // namespace clang

clang/include/clang/Basic/DeclNodes.td

@@ -70,6 +70,7 @@ def Named : Decl<"named declarations", 1>;
       def TypeAliasTemplate : DDecl<RedeclarableTemplate>;
     def TemplateTemplateParm : DDecl<Template>;
     def BuiltinTemplate : DDecl<Template>;
+    def Concept : DDecl<Template>;
   def Using : DDecl<Named>;
   def UsingPack : DDecl<Named>;
   def UsingShadow : DDecl<Named>;

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -684,7 +684,7 @@ def warn_cxx14_compat_template_template_param_typename : Warning<
 def err_template_spec_syntax_non_template : Error<
   "identifier followed by '<' indicates a class template specialization but "
   "%0 %select{does not refer to a template|refers to a function template|"
-  "<unused>|refers to a variable template|<unused>}1">;
+  "<unused>|refers to a variable template|<unused>|refers to a concept}1">;
 def err_id_after_template_in_nested_name_spec : Error<
   "expected template name after 'template' keyword in nested name specifier">;
 def err_unexpected_template_in_unqualified_id : Error<
@@ -1287,4 +1287,12 @@ def err_for_co_await_not_range_for : Error<
   "'co_await' modifier can only be applied to range-based for loop">;
 }
 
+let CategoryName = "Concepts Issue" in {
+def err_concept_definition_not_identifier : Error<
+  "name defined in concept definition must be an identifier">;
+def ext_concept_legacy_bool_keyword : ExtWarn<
+  "ISO C++2a does not permit the 'bool' keyword after 'concept'">,
+  InGroup<DiagGroup<"concepts-ts-compat">>;
+}
+
 } // end of Parser diagnostics

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -2010,8 +2010,8 @@ def err_auto_not_allowed : Error<
   "%select{'auto'|'decltype(auto)'|'__auto_type'|"
   "use of "
   "%select{class template|function template|variable template|alias template|"
-  "template template parameter|template}2 %3 requires template arguments; "
-  "argument deduction}0 not allowed "
+  "template template parameter|concept|template}2 %3 requires template "
+  "arguments; argument deduction}0 not allowed "
   "%select{in function prototype"
   "|in non-static struct member|in struct member"
   "|in non-static union member|in union member"
@@ -2100,8 +2100,8 @@ def err_deduced_class_template_compound_type : Error<
   "deduced class template specialization type">;
 def err_deduced_non_class_template_specialization_type : Error<
   "%select{<error>|function template|variable template|alias template|"
-  "template template parameter|template}0 %1 requires template arguments; "
-  "argument deduction only allowed for class templates">;
+  "template template parameter|concept|template}0 %1 requires template "
+  "arguments; argument deduction only allowed for class templates">;
 def err_deduced_class_template_ctor_ambiguous : Error<
   "ambiguous deduction for template arguments of %0">;
 def err_deduced_class_template_ctor_no_viable : Error<
@@ -2128,7 +2128,7 @@ def err_deduction_guide_invalid_specifier : Error<
 def err_deduction_guide_name_not_class_template : Error<
   "cannot specify deduction guide for "
   "%select{<error>|function template|variable template|alias template|"
-  "template template parameter|dependent template name}0 %1">;
+  "template template parameter|concept|dependent template name}0 %1">;
 def err_deduction_guide_wrong_scope : Error<
   "deduction guide must be declared in the same scope as template %q0">;
 def err_deduction_guide_defines_function : Error<
@@ -2456,32 +2456,20 @@ def warn_private_extern : Warning<
 def note_private_extern : Note<
   "use __attribute__((visibility(\"hidden\"))) attribute instead">;
 
-// C++ Concepts TS
-def err_concept_wrong_decl_kind : Error<
-  "'concept' can only appear on the definition of a function template or variable template">;
-def err_concept_decls_may_only_appear_in_namespace_scope : Error<
-  "concept declarations may only appear in namespace scope">;
-def err_function_concept_not_defined : Error<
-  "function concept declaration must be a definition">;
-def err_var_concept_not_initialized : Error<
-  "variable concept declaration must be initialized">;
-def err_function_concept_exception_spec : Error<
-  "function concept cannot have exception specification">;
-def err_concept_decl_invalid_specifiers : Error<
-  "%select{variable|function}0 concept cannot be declared "
-  "'%select{thread_local|inline|friend|constexpr}1'">;
-def err_function_concept_with_params : Error<
-  "function concept cannot have any parameters">;
-def err_function_concept_bool_ret : Error<
-  "declared return type of function concept must be 'bool'">;
-def err_variable_concept_bool_decl : Error<
-  "declared type of variable concept must be 'bool'">;
-def err_concept_specified_specialization : Error<
-  "'concept' cannot be applied on an "
-  "%select{explicit instantiation|explicit specialization|partial specialization}0">;
-def err_concept_specialized : Error<
-  "%select{function|variable}0 concept cannot be "
-  "%select{explicitly instantiated|explicitly specialized|partially specialized}1">;
+// C++ Concepts
+def err_concept_initialized_with_non_bool_type : Error<
+  "constraint expression must be of type 'bool' but is of type %0">;
+def err_concept_decls_may_only_appear_in_global_namespace_scope : Error<
+  "concept declarations may only appear in global or namespace scope">;
+def err_concept_no_parameters : Error<
+  "concept template parameter list must have at least one parameter; explicit "
+  "specialization of concepts is not allowed">;
+def err_concept_extra_headers : Error<
+  "extraneous template parameter list in concept definition">;
+def err_concept_no_associated_constraints : Error<
+  "concept cannot have associated constraints">;
+def err_concept_not_implemented : Error<
+  "sorry, unimplemented concepts feature %0 used">;
 
 def err_template_different_associated_constraints : Error<
   "associated constraints differ in template redeclaration">;
@@ -4019,11 +4007,12 @@ def ext_adl_only_template_id : ExtWarn<
 def err_template_missing_args : Error<
   "use of "
   "%select{class template|function template|variable template|alias template|"
-  "template template parameter|template}0 %1 requires template arguments">;
+  "template template parameter|concept|template}0 %1 requires template "
+  "arguments">;
 def err_template_arg_list_different_arity : Error<
   "%select{too few|too many}0 template arguments for "
   "%select{class template|function template|variable template|alias template|"
-  "template template parameter|template}1 %2">;
+  "template template parameter|concept|template}1 %2">;
 def note_template_decl_here : Note<"template is declared here">;
 def err_template_arg_must_be_type : Error<
   "template argument for template type parameter must be a type">;

clang/include/clang/Basic/TemplateKinds.h

@@ -48,9 +48,9 @@ enum TemplateNameKind {
   /// anyway. In C++20, this is mandatory in order to parse ADL-only function
   /// template specialization calls.
   TNK_Undeclared_template,
+  /// The name refers to a concept.
+  TNK_Concept_template,
 };
 
 }
 #endif
-
-

clang/include/clang/Parse/Parser.h

@@ -3024,6 +3024,10 @@ class Parser : public CodeCompletionHandler {
                                    SourceLocation &DeclEnd,
                                    ParsedAttributes &AccessAttrs,
                                    AccessSpecifier AS = AS_none);
+  // C++2a: Template, concept definition [temp]
+  Decl *
+  ParseConceptDefinition(const ParsedTemplateInfo &TemplateInfo,
+                         SourceLocation &DeclEnd);
 
   //===--------------------------------------------------------------------===//
   // Modules

clang/include/clang/Sema/Sema.h

@@ -1973,6 +1973,7 @@ class Sema {
     VarTemplate,
     AliasTemplate,
     TemplateTemplateParam,
+    Concept,
     DependentTemplate
   };
   TemplateNameKindForDiagnostics
@@ -6551,6 +6552,13 @@ class Sema {
                                 SourceLocation TemplateLoc,
                                 const TemplateArgumentListInfo *TemplateArgs);
 
+  ExprResult
+  CheckConceptTemplateId(const CXXScopeSpec &SS,
+                         const DeclarationNameInfo &NameInfo,
+                         ConceptDecl *Template,
+                         SourceLocation TemplateLoc,
+                         const TemplateArgumentListInfo *TemplateArgs);
+
   void diagnoseMissingTemplateArguments(TemplateName Name, SourceLocation Loc);
 
   ExprResult BuildTemplateIdExpr(const CXXScopeSpec &SS,
@@ -6818,6 +6826,11 @@ class Sema {
                                   const TemplateArgument *Args,
                                   unsigned NumArgs);
 
+  // Concepts
+  Decl *ActOnConceptDefinition(
+      Scope *S, MultiTemplateParamsArg TemplateParameterLists,
+      IdentifierInfo *Name, SourceLocation NameLoc, Expr *ConstraintExpr);
+
   //===--------------------------------------------------------------------===//
   // C++ Variadic Templates (C++0x [temp.variadic])
   //===--------------------------------------------------------------------===//

clang/include/clang/Serialization/ASTBitCodes.h

@@ -1489,7 +1489,10 @@ namespace serialization {
       /// A TypeAliasTemplateDecl record.
       DECL_TYPE_ALIAS_TEMPLATE,
 
-      /// A StaticAssertDecl record.
+      /// \brief A ConceptDecl record.
+      DECL_CONCEPT,
+
+      /// \brief A StaticAssertDecl record.
       DECL_STATIC_ASSERT,
 
       /// A record containing CXXBaseSpecifiers.

clang/lib/AST/ASTStructuralEquivalence.cpp

@@ -1512,6 +1512,18 @@ static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
                                   D2->getTemplatedDecl()->getType());
 }
 
+static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
+                                     ConceptDecl *D1,
+                                     ConceptDecl *D2) {
+  // Check template parameters.
+  if (!IsTemplateDeclCommonStructurallyEquivalent(Context, D1, D2))
+    return false;
+
+  // Check the constraint expression.
+  return IsStructurallyEquivalent(Context, D1->getConstraintExpr(),
+                                  D2->getConstraintExpr());
+}
+
 static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
                                      FriendDecl *D1, FriendDecl *D2) {
   if ((D1->getFriendType() && D2->getFriendDecl()) ||
@@ -1771,6 +1783,14 @@ bool StructuralEquivalenceContext::CheckKindSpecificEquivalence(
       // Class template/non-class-template mismatch.
       return false;
     }
+  } else if (auto *ConceptDecl1 = dyn_cast<ConceptDecl>(D1)) {
+    if (auto *ConceptDecl2 = dyn_cast<ConceptDecl>(D2)) {
+      if (!::IsStructurallyEquivalent(*this, ConceptDecl1, ConceptDecl2))
+        return false;
+    } else {
+      // Concept/non-concept mismatch.
+      return false;
+    }
   } else if (auto *TTP1 = dyn_cast<TemplateTypeParmDecl>(D1)) {
     if (auto *TTP2 = dyn_cast<TemplateTypeParmDecl>(D2)) {
       if (!::IsStructurallyEquivalent(*this, TTP1, TTP2))

clang/lib/AST/DeclBase.cpp

@@ -710,6 +710,7 @@ unsigned Decl::getIdentifierNamespaceForKind(Kind DeclKind) {
     case Binding:
     case NonTypeTemplateParm:
     case VarTemplate:
+    case Concept:
       // These (C++-only) declarations are found by redeclaration lookup for
       // tag types, so we include them in the tag namespace.
       return IDNS_Ordinary | IDNS_Tag;

clang/lib/AST/DeclPrinter.cpp

@@ -1123,8 +1123,13 @@ void DeclPrinter::VisitTemplateDecl(const TemplateDecl *D) {
     if (TTP->isParameterPack())
       Out << "...";
     Out << D->getName();
-  } else {
-    Visit(D->getTemplatedDecl());
+  } else if (auto *TD = D->getTemplatedDecl())
+    Visit(TD);
+  else if (const auto *Concept = dyn_cast<ConceptDecl>(D)) {
+    Out << "concept " << Concept->getName() << " = " ;
+    Concept->getConstraintExpr()->printPretty(Out, nullptr, Policy,
+                                              Indentation);
+    Out << ";";
   }
 }
 

clang/lib/AST/DeclTemplate.cpp

@@ -821,6 +821,26 @@ ClassTemplateSpecializationDecl::getSourceRange() const {
   }
 }
 
+//===----------------------------------------------------------------------===//
+// ConceptDecl Implementation
+//===----------------------------------------------------------------------===//
+ConceptDecl *ConceptDecl::Create(ASTContext &C, DeclContext *DC,
+                                 SourceLocation L, DeclarationName Name,
+                                 TemplateParameterList *Params,
+                                 Expr *ConstraintExpr) {
+  AdoptTemplateParameterList(Params, DC);
+  return new (C, DC) ConceptDecl(DC, L, Name, Params, ConstraintExpr);
+}
+
+ConceptDecl *ConceptDecl::CreateDeserialized(ASTContext &C,
+                                             unsigned ID) {
+  ConceptDecl *Result = new (C, ID) ConceptDecl(nullptr, SourceLocation(),
+                                                DeclarationName(),
+                                                nullptr, nullptr);
+
+  return Result;
+}
+
 //===----------------------------------------------------------------------===//
 // ClassTemplatePartialSpecializationDecl Implementation
 //===----------------------------------------------------------------------===//

clang/lib/AST/TextNodeDumper.cpp

@@ -1936,3 +1936,7 @@ void TextNodeDumper::VisitBlockDecl(const BlockDecl *D) {
   if (D->capturesCXXThis())
     OS << " captures_this";
 }
+
+void TextNodeDumper::VisitConceptDecl(const ConceptDecl *D) {
+  dumpName(D);
+}

clang/lib/CodeGen/CGDecl.cpp

@@ -108,6 +108,7 @@ void CodeGenFunction::EmitDecl(const Decl &D) {
   case Decl::OMPCapturedExpr:
   case Decl::OMPRequires:
   case Decl::Empty:
+  case Decl::Concept:
     // None of these decls require codegen support.
     return;
 

clang/lib/CodeGen/CodeGenModule.cpp

@@ -5162,6 +5162,7 @@ void CodeGenModule::EmitTopLevelDecl(Decl *D) {
   case Decl::UsingShadow:
   case Decl::ClassTemplate:
   case Decl::VarTemplate:
+  case Decl::Concept:
   case Decl::VarTemplatePartialSpecialization:
   case Decl::FunctionTemplate:
   case Decl::TypeAliasTemplate:

clang/lib/Index/IndexDecl.cpp

@@ -652,10 +652,10 @@ class IndexingDeclVisitor : public ConstDeclVisitor<IndexingDeclVisitor, bool> {
   }
 
   static bool shouldIndexTemplateParameterDefaultValue(const NamedDecl *D) {
-    if (!D)
-      return false;
     // We want to index the template parameters only once when indexing the
     // canonical declaration.
+    if (!D)
+      return false;
     if (const auto *FD = dyn_cast<FunctionDecl>(D))
       return FD->getCanonicalDecl() == FD;
     else if (const auto *TD = dyn_cast<TagDecl>(D))