From 4fa14515aca80a81ffd07ec51fa66bca539d8e07 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Thu, 21 Dec 2017 19:43:39 +0000
Subject: [PATCH] When instantiating a deduction guide, transform its name.

Otherwise it will serve as a deduction guide for the wrong class template.

llvm-svn: 321297
---
 clang/lib/Sema/SemaTemplateInstantiateDecl.cpp      | 10 +++++++---
 clang/test/SemaTemplate/nested-deduction-guides.cpp | 13 +++++++++++++
 2 files changed, 20 insertions(+), 3 deletions(-)
 create mode 100644 clang/test/SemaTemplate/nested-deduction-guides.cpp

diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index b926e573ade6..1deb8638756b 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1587,9 +1587,10 @@ static QualType adjustFunctionTypeForInstantiation(ASTContext &Context,
 }
 
 /// Normal class members are of more specific types and therefore
-/// don't make it here.  This function serves two purposes:
+/// don't make it here.  This function serves three purposes:
 ///   1) instantiating function templates
 ///   2) substituting friend declarations
+///   3) substituting deduction guide declarations for nested class templates
 Decl *TemplateDeclInstantiator::VisitFunctionDecl(FunctionDecl *D,
                                        TemplateParameterList *TemplateParams) {
   // Check whether there is already a function template specialization for
@@ -1650,16 +1651,19 @@ Decl *TemplateDeclInstantiator::VisitFunctionDecl(FunctionDecl *D,
                                          TemplateArgs);
   }
 
+  DeclarationNameInfo NameInfo
+    = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);
+
   FunctionDecl *Function;
   if (auto *DGuide = dyn_cast<CXXDeductionGuideDecl>(D)) {
     Function = CXXDeductionGuideDecl::Create(
       SemaRef.Context, DC, D->getInnerLocStart(), DGuide->isExplicit(),
-      D->getNameInfo(), T, TInfo, D->getSourceRange().getEnd());
+      NameInfo, T, TInfo, D->getSourceRange().getEnd());
     if (DGuide->isCopyDeductionCandidate())
       cast<CXXDeductionGuideDecl>(Function)->setIsCopyDeductionCandidate();
   } else {
     Function = FunctionDecl::Create(
-        SemaRef.Context, DC, D->getInnerLocStart(), D->getNameInfo(), T, TInfo,
+        SemaRef.Context, DC, D->getInnerLocStart(), NameInfo, T, TInfo,
         D->getCanonicalDecl()->getStorageClass(), D->isInlineSpecified(),
         D->hasWrittenPrototype(), D->isConstexpr());
     Function->setRangeEnd(D->getSourceRange().getEnd());
diff --git a/clang/test/SemaTemplate/nested-deduction-guides.cpp b/clang/test/SemaTemplate/nested-deduction-guides.cpp
new file mode 100644
index 000000000000..2c5dda456a13
--- /dev/null
+++ b/clang/test/SemaTemplate/nested-deduction-guides.cpp
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -std=c++17 -verify %s
+// expected-no-diagnostics
+
+template<typename T> struct A {
+  template<typename U> struct B {
+    B(...);
+  };
+  template<typename U> B(U) -> B<U>;
+};
+A<void>::B b = 123;
+
+using T = decltype(b);
+using T = A<void>::B<int>;