4 files changed, 19 insertions, 7 deletions

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 20c6cbec572..d8790768cb3 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -9345,9 +9345,11 @@ ASTReader::ReadTemplateParameterList(ModuleFile &F,
   while (NumParams--)
     Params.push_back(ReadDeclAs<NamedDecl>(F, Record, Idx));
 
-  // TODO: Concepts
+  bool HasRequiresClause = Record[Idx++];
+  Expr *RequiresClause = HasRequiresClause ? ReadExpr(F) : nullptr;
+
   TemplateParameterList *TemplateParams = TemplateParameterList::Create(
-      getContext(), TemplateLoc, LAngleLoc, Params, RAngleLoc, nullptr);
+      getContext(), TemplateLoc, LAngleLoc, Params, RAngleLoc, RequiresClause);
   return TemplateParams;
 }
 
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index d906286db54..65d62524e22 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2000,7 +2000,6 @@ DeclID ASTDeclReader::VisitTemplateDecl(TemplateDecl *D) {
   DeclID PatternID = ReadDeclID();
   auto *TemplatedDecl = cast_or_null<NamedDecl>(Reader.GetDecl(PatternID));
   TemplateParameterList *TemplateParams = Record.readTemplateParameterList();
-  // FIXME handle associated constraints
   D->init(TemplatedDecl, TemplateParams);
 
   return PatternID;
@@ -2166,7 +2165,8 @@ void ASTDeclReader::VisitClassTemplatePartialSpecializationDecl(
                                     ClassTemplatePartialSpecializationDecl *D) {
   RedeclarableResult Redecl = VisitClassTemplateSpecializationDeclImpl(D);
 
-  D->TemplateParams = Record.readTemplateParameterList();
+  TemplateParameterList *Params = Record.readTemplateParameterList();
+  D->TemplateParams = Params;
   D->ArgsAsWritten = Record.readASTTemplateArgumentListInfo();
 
   // These are read/set from/to the first declaration.
@@ -2268,7 +2268,8 @@ void ASTDeclReader::VisitVarTemplatePartialSpecializationDecl(
     VarTemplatePartialSpecializationDecl *D) {
   RedeclarableResult Redecl = VisitVarTemplateSpecializationDeclImpl(D);
 
-  D->TemplateParams = Record.readTemplateParameterList();
+  TemplateParameterList *Params = Record.readTemplateParameterList();
+  D->TemplateParams = Params;
   D->ArgsAsWritten = Record.readASTTemplateArgumentListInfo();
 
   // These are read/set from/to the first declaration.
@@ -2284,6 +2285,7 @@ void ASTDeclReader::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
 
   D->setDeclaredWithTypename(Record.readInt());
 
+  // TODO: Concepts: Immediately introduced constraint
   if (Record.readInt())
     D->setDefaultArgument(GetTypeSourceInfo());
 }
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 5e9e650fce8..aef35231163 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -6070,10 +6070,16 @@ void ASTRecordWriter::AddTemplateParameterList(
   AddSourceLocation(TemplateParams->getTemplateLoc());
   AddSourceLocation(TemplateParams->getLAngleLoc());
   AddSourceLocation(TemplateParams->getRAngleLoc());
-  // TODO: Concepts
+
   Record->push_back(TemplateParams->size());
   for (const auto &P : *TemplateParams)
     AddDeclRef(P);
+  if (const Expr *RequiresClause = TemplateParams->getRequiresClause()) {
+    Record->push_back(true);
+    AddStmt(const_cast<Expr*>(RequiresClause));
+  } else {
+    Record->push_back(false);
+  }
 }
 
 /// Emit a template argument list.
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 2c22587957e..039b57f88e7 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1608,7 +1608,7 @@ void ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D) {
   VisitTypeDecl(D);
 
   Record.push_back(D->wasDeclaredWithTypename());
-
+  // TODO: Concepts - constrained parameters.
   bool OwnsDefaultArg = D->hasDefaultArgument() &&
                         !D->defaultArgumentWasInherited();
   Record.push_back(OwnsDefaultArg);
@@ -1638,6 +1638,7 @@ void ASTDeclWriter::VisitNonTypeTemplateParmDecl(NonTypeTemplateParmDecl *D) {
 
     Code = serialization::DECL_EXPANDED_NON_TYPE_TEMPLATE_PARM_PACK;
   } else {
+    // TODO: Concepts - constrained parameters.
     // Rest of NonTypeTemplateParmDecl.
     Record.push_back(D->isParameterPack());
     bool OwnsDefaultArg = D->hasDefaultArgument() &&
@@ -1667,6 +1668,7 @@ void ASTDeclWriter::VisitTemplateTemplateParmDecl(TemplateTemplateParmDecl *D) {
       Record.AddTemplateParameterList(D->getExpansionTemplateParameters(I));
     Code = serialization::DECL_EXPANDED_TEMPLATE_TEMPLATE_PARM_PACK;
   } else {
+    // TODO: Concepts - constrained parameters.
     // Rest of TemplateTemplateParmDecl.
     Record.push_back(D->isParameterPack());
     bool OwnsDefaultArg = D->hasDefaultArgument() &&