Clean up handling of constrained parameters in lambdas.

No functionality change intended.

clang/lib/AST/TypePrinter.cpp

@@ -1125,7 +1125,9 @@ void TypePrinter::printAutoBefore(const AutoType *T, raw_ostream &OS) {
     printBefore(T->getDeducedType(), OS);
   } else {
     if (T->isConstrained()) {
-      OS << T->getTypeConstraintConcept()->getName();
+      // FIXME: Track a TypeConstraint as type sugar, so that we can print the
+      // type as it was written.
+      T->getTypeConstraintConcept()->getDeclName().print(OS, Policy);
       auto Args = T->getTypeConstraintArguments();
       if (!Args.empty())
         printTemplateArgumentList(

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -2386,10 +2386,10 @@ ParmVarDecl *Sema::SubstParmVarDecl(ParmVarDecl *OldParm,
         }
         if (AttachTypeConstraint(
                 TC->getNestedNameSpecifierLoc(), TC->getConceptNameInfo(),
-                TC->getNamedConcept(), &InstArgs, Inst,
+                TC->getNamedConcept(), TemplArgInfo ? &InstArgs : nullptr, Inst,
                 TTP->isParameterPack()
                     ? cast<CXXFoldExpr>(TC->getImmediatelyDeclaredConstraint())
-                        ->getEllipsisLoc()
+                          ->getEllipsisLoc()
                     : SourceLocation()))
           return nullptr;
       }

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -2581,7 +2581,6 @@ Decl *TemplateDeclInstantiator::VisitParmVarDecl(ParmVarDecl *D) {
 
 Decl *TemplateDeclInstantiator::VisitTemplateTypeParmDecl(
                                                     TemplateTypeParmDecl *D) {
-  // TODO: don't always clone when decls are refcounted.
   assert(D->getTypeForDecl()->isTemplateTypeParmType());
 
   Optional<unsigned> NumExpanded;

clang/lib/Sema/TreeTransform.h

@@ -6515,11 +6515,9 @@ QualType TreeTransform<Derived>::TransformAutoType(TypeLocBuilder &TLB,
   ConceptDecl *NewCD = nullptr;
   TemplateArgumentListInfo NewTemplateArgs;
   NestedNameSpecifierLoc NewNestedNameSpec;
-  if (TL.getTypePtr()->isConstrained()) {
-    NewCD = cast_or_null<ConceptDecl>(
-        getDerived().TransformDecl(
-            TL.getConceptNameLoc(),
-            TL.getTypePtr()->getTypeConstraintConcept()));
+  if (T->isConstrained()) {
+    NewCD = cast_or_null<ConceptDecl>(getDerived().TransformDecl(
+        TL.getConceptNameLoc(), T->getTypeConstraintConcept()));
 
     NewTemplateArgs.setLAngleLoc(TL.getLAngleLoc());
     NewTemplateArgs.setRAngleLoc(TL.getRAngleLoc());
@@ -6541,7 +6539,8 @@ QualType TreeTransform<Derived>::TransformAutoType(TypeLocBuilder &TLB,
 
   QualType Result = TL.getType();
   if (getDerived().AlwaysRebuild() || NewDeduced != OldDeduced ||
-      T->isDependentType()) {
+      T->isDependentType() || T->isConstrained()) {
+    // FIXME: Maybe don't rebuild if all template arguments are the same.
     llvm::SmallVector<TemplateArgument, 4> NewArgList;
     NewArgList.reserve(NewArgList.size());
     for (const auto &ArgLoc : NewTemplateArgs.arguments())