From c799a6a5c884831c3c3ea57d30fbe4ab35709d49 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Wed, 25 Apr 2012 23:23:48 +0000
Subject: [PATCH] If a type is non-literal by virtue of being incomplete
 produce notes explaining that.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@155598 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/clang/Basic/DiagnosticSemaKinds.td | 2 ++
 lib/Sema/SemaType.cpp                      | 9 +++++++--
 test/CXX/basic/basic.types/p10.cpp         | 6 +++---
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index f9fb2bb4fb..b0e5deba51 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1367,6 +1367,8 @@ def err_constexpr_virtual : Error<"virtual function cannot be constexpr">;
 def err_constexpr_virtual_base : Error<
   "constexpr %select{member function|constructor}0 not allowed in "
   "%select{class|struct}1 with virtual base %plural{1:class|:classes}2">;
+def note_non_literal_incomplete : Note<
+  "incomplete type %0 is not a literal type">;
 def note_non_literal_virtual_base : Note<"%select{class|struct}0 with virtual "
   "base %plural{1:class|:classes}1 is not a literal type">;
 def note_constexpr_virtual_base_here : Note<"virtual base class declared here">;
diff --git a/lib/Sema/SemaType.cpp b/lib/Sema/SemaType.cpp
index 1b95f05c79..8b237c8a3c 100644
--- a/lib/Sema/SemaType.cpp
+++ b/lib/Sema/SemaType.cpp
@@ -4301,9 +4301,14 @@ bool Sema::RequireLiteralType(SourceLocation Loc, QualType T,
 
   const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
 
-  // FIXME: Better diagnostic for incomplete class?
-  if (!RD->isCompleteDefinition())
+  // A partially-defined class type can't be a literal type, because a literal
+  // class type must have a trivial destructor (which can't be checked until
+  // the class definition is complete).
+  if (!RD->isCompleteDefinition()) {
+    RequireCompleteType(Loc, ElemType,
+                        PDiag(diag::note_non_literal_incomplete) << T);
     return true;
+  }
 
   // If the class has virtual base classes, then it's not an aggregate, and
   // cannot have any constexpr constructors or a trivial default constructor,
diff --git a/test/CXX/basic/basic.types/p10.cpp b/test/CXX/basic/basic.types/p10.cpp
index 83b910b606..191d42bebd 100644
--- a/test/CXX/basic/basic.types/p10.cpp
+++ b/test/CXX/basic/basic.types/p10.cpp
@@ -22,11 +22,11 @@ struct BeingDefined {
 
 // (implied) - it is complete
 
-struct Incomplete;
+struct Incomplete; // expected-note 2{{forward declaration of 'Incomplete'}}
 template<class T> struct ClassTemp {};
 
-constexpr Incomplete incomplete = {}; // expected-error {{constexpr variable cannot have non-literal type 'const Incomplete'}}
-constexpr Incomplete incomplete2[] = {}; // expected-error {{constexpr variable cannot have non-literal type 'Incomplete const[]'}}
+constexpr Incomplete incomplete = {}; // expected-error {{constexpr variable cannot have non-literal type 'const Incomplete'}} expected-note {{incomplete type 'const Incomplete' is not a literal type}}
+constexpr Incomplete incomplete2[] = {}; // expected-error {{constexpr variable cannot have non-literal type 'Incomplete const[]'}} expected-note {{incomplete type 'Incomplete const[]' is not a literal type}}
 constexpr ClassTemp<int> classtemplate = {};
 constexpr ClassTemp<int> classtemplate2[] = {};
 
-- 
2.40.0