[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Zhihao Yuan via Phabricator via cfe-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rC328409: [C++17] Fix class template argument deduction for 
default constructors without… (authored by lichray, committed by ).

Repository:
  rC Clang

https://reviews.llvm.org/D38216

Files:
  lib/Sema/SemaDecl.cpp
  test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
  test/Parser/cxx1z-class-template-argument-deduction.cpp


Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are 
permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
@@ -16,3 +15,5 @@
   static A a; // expected-error {{requires an initializer}}
 };
 extern A x; // expected-error {{requires an initializer}}
+static A y;
+
Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -137,7 +137,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -150,7 +149,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' 
requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring 
variable with deduced class template specialization type}}
Index: lib/Sema/SemaDecl.cpp
===
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10396,12 +10396,22 @@
   // C++11 [dcl.spec.auto]p3
   if (!Init) {
 assert(VDecl && "no init for init capture deduction?");
-Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
-  << VDecl->getDeclName() << Type;
-return QualType();
+
+// Except for class argument deduction, and then for an initializing
+// declaration only, i.e. no static at class scope or extern.
+if (!isa(Deduced) ||
+VDecl->hasExternalStorage() ||
+VDecl->isStaticDataMember()) {
+  Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
+<< VDecl->getDeclName() << Type;
+  return QualType();
+}
   }
 
-  ArrayRef DeduceInits = Init;
+  ArrayRef DeduceInits;
+  if (Init)
+DeduceInits = Init;
+
   if (DirectInit) {
 if (auto *PL = dyn_cast_or_null(Init))
   DeduceInits = PL->exprs();


Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
@@ -16,3 +15,5 @@
   static A a; // expected-error {{requires an initializer}}
 };
 extern A x; // expected-error {{requires an initializer}}
+static A y;
+
Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -137,7 +137,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -150,7 +149,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring variable with deduced class template specialization type}}
Index: lib/Sema/SemaDecl.cpp
===
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10396,12 +10396,22 @@
   // C++11 [dcl.spec.auto]p3
   if (!Init) {
 assert(VDecl && "no init for init capture deduction?");
-Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
-  << VDecl->getDeclName() << Type;
-return QualType();
+
+// Except for class argument deduction, and then for an initializing
+// declaration only, i.e. no static at class scope or extern.

[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith accepted this revision.
rsmith added inline comments.
This revision is now accepted and ready to land.



Comment at: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp:17
 };
 extern A x; // expected-error {{requires an initializer}}
+static A y;

The diagnostic we produce in this case is not very good. The problem is not 
that the declaration requires an initializer (how can a forward declaration 
like this require an initializer?), instead the problem is that type deduction 
is only possible for the initializing declaration of a variable.


https://reviews.llvm.org/D38216



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[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Nicolas Lesser via Phabricator via cfe-commits]

Rakete updated this revision to Diff 138862.
Rakete added a comment.

@lichray Ok done :) Thanks for reviewing


https://reviews.llvm.org/D38216

Files:
  lib/Sema/SemaDecl.cpp
  test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
  test/Parser/cxx1z-class-template-argument-deduction.cpp


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -137,7 +137,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -150,7 +149,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' 
requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring 
variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are 
permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
@@ -16,3 +15,5 @@
   static A a; // expected-error {{requires an initializer}}
 };
 extern A x; // expected-error {{requires an initializer}}
+static A y;
+
Index: lib/Sema/SemaDecl.cpp
===
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10396,12 +10396,22 @@
   // C++11 [dcl.spec.auto]p3
   if (!Init) {
 assert(VDecl && "no init for init capture deduction?");
-Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
-  << VDecl->getDeclName() << Type;
-return QualType();
+
+// Except for class argument deduction, and then for an initializing
+// declaration only, i.e. no static at class scope or extern.
+if (!isa(Deduced) ||
+VDecl->hasExternalStorage() ||
+VDecl->isStaticDataMember()) {
+  Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
+<< VDecl->getDeclName() << Type;
+  return QualType();
+}
   }
 
-  ArrayRef DeduceInits = Init;
+  ArrayRef DeduceInits;
+  if (Init)
+DeduceInits = Init;
+
   if (DirectInit) {
 if (auto *PL = dyn_cast_or_null(Init))
   DeduceInits = PL->exprs();


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -137,7 +137,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -150,7 +149,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
@@ -16,3 +15,5 @@
   static A a; // expected-error {{requires an initializer}}
 };
 extern A x; // expected-error {{requires an initializer}}
+static A y;
+
Index: lib/Sema/SemaDecl.cpp
===
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10396,12 +10396,22 @@
   // C++11 [dcl.spec.auto]p3
   if (!Init) {
 assert(VDecl && "no init for init capture deduction?");
-Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
-  << VDecl->getDeclName() << Type;
-return QualType();
+
+// Except for class argument deduction, and then for an initializing
+// declaration only, i.e. no static at class scope or extern.
+if (!isa(Deduced) ||
+VDecl->hasExternalStorage() ||
+VDecl->isStaticDataMember()) {
+  

[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Zhihao Yuan via Phabricator via cfe-commits]

lichray added a comment.

LGTM




Comment at: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp:17
 };
 extern A x; // expected-error {{requires an initializer}}

Please add one more test to the end of the file saying
```
static A y;
```
as a remainder to the readers.


https://reviews.llvm.org/D38216



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[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Nicolas Lesser via Phabricator via cfe-commits]

Rakete updated this revision to Diff 138187.
Rakete added a comment.

Addressed review comments :)

Thanks!


https://reviews.llvm.org/D38216

Files:
  lib/Sema/SemaDecl.cpp
  test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
  test/Parser/cxx1z-class-template-argument-deduction.cpp


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -137,7 +137,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -150,7 +149,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' 
requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring 
variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are 
permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
Index: lib/Sema/SemaDecl.cpp
===
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10395,12 +10395,22 @@
   // C++11 [dcl.spec.auto]p3
   if (!Init) {
 assert(VDecl && "no init for init capture deduction?");
-Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
-  << VDecl->getDeclName() << Type;
-return QualType();
+
+// Except for class argument deduction, and then for an initializing
+// declaration only, i.e. no static at class scope or extern.
+if (!isa(Deduced) ||
+VDecl->hasExternalStorage() ||
+VDecl->isStaticDataMember()) {
+  Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
+<< VDecl->getDeclName() << Type;
+  return QualType();
+}
   }
 
-  ArrayRef DeduceInits = Init;
+  ArrayRef DeduceInits;
+  if (Init)
+DeduceInits = Init;
+
   if (DirectInit) {
 if (auto *PL = dyn_cast_or_null(Init))
   DeduceInits = PL->exprs();


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -137,7 +137,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -150,7 +149,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
Index: lib/Sema/SemaDecl.cpp
===
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10395,12 +10395,22 @@
   // C++11 [dcl.spec.auto]p3
   if (!Init) {
 assert(VDecl && "no init for init capture deduction?");
-Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
-  << VDecl->getDeclName() << Type;
-return QualType();
+
+// Except for class argument deduction, and then for an initializing
+// declaration only, i.e. no static at class scope or extern.
+if (!isa(Deduced) ||
+VDecl->hasExternalStorage() ||
+VDecl->isStaticDataMember()) {
+  Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
+<< VDecl->getDeclName() << Type;
+  return QualType();
+}
   }
 
-  ArrayRef DeduceInits = Init;
+  ArrayRef DeduceInits;
+  if (Init)
+DeduceInits = Init;
+
   if (DirectInit) {
 if (auto *PL = dyn_cast_or_null(Init))
   

[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith requested changes to this revision.
rsmith added a comment.
This revision now requires changes to proceed.

Per [dcl.type.class.deduct]p1, only the initializing declaration of a variable 
can use a placeholder type. The existing diagnostic was correct in many of the 
modified cases.




Comment at: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp:15
 struct B {
-  static A a; // expected-error {{requires an initializer}}
+  static A a;
 };

This should be ill-formed: this is not the initializing declaration of `B::a`.



Comment at: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp:17
 };
-extern A x; // expected-error {{requires an initializer}}
+extern A x;

Likewise, this should remain ill-formed.



Comment at: test/Parser/cxx1z-class-template-argument-deduction.cpp:55
 
-  static A x; // expected-error {{declaration of variable 'x' with deduced 
type 'A' requires an initializer}}
+  static A x;
   static constexpr A y = 0;

Likewise.


https://reviews.llvm.org/D38216



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[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Nicolas Lesser via Phabricator via cfe-commits]

Rakete updated this revision to Diff 128662.
Rakete marked an inline comment as done.
Rakete added a comment.

Rebased + friendly 2018 ping


https://reviews.llvm.org/D38216

Files:
  lib/Sema/SemaDecl.cpp
  test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
  test/Parser/cxx1z-class-template-argument-deduction.cpp


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -52,7 +52,7 @@
 
   operator A(); // expected-error {{requires template arguments; argument 
deduction not allowed in conversion function type}}
 
-  static A x; // expected-error {{declaration of variable 'x' with deduced 
type 'A' requires an initializer}}
+  static A x;
   static constexpr A y = 0;
 };
 
@@ -114,7 +114,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -127,7 +126,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' 
requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring 
variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,14 +5,13 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are 
permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
 A f(0), g{}; // expected-error {{template arguments deduced as 'A' in 
declaration of 'f' and deduced as 'A' in declaration of 'g'}}
 
 struct B {
-  static A a; // expected-error {{requires an initializer}}
+  static A a;
 };
-extern A x; // expected-error {{requires an initializer}}
+extern A x;
Index: lib/Sema/SemaDecl.cpp
===
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10053,14 +10053,18 @@
   assert(Deduced && "deduceVarTypeFromInitializer for non-deduced type");
 
   // C++11 [dcl.spec.auto]p3
-  if (!Init) {
+  // Except for class argument deduction.
+  if (!Init && !isa(Deduced)) {
 assert(VDecl && "no init for init capture deduction?");
 Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
   << VDecl->getDeclName() << Type;
 return QualType();
   }
 
-  ArrayRef DeduceInits = Init;
+  ArrayRef DeduceInits;
+  if (Init)
+DeduceInits = Init;
+
   if (DirectInit) {
 if (auto *PL = dyn_cast_or_null(Init))
   DeduceInits = PL->exprs();


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -52,7 +52,7 @@
 
   operator A(); // expected-error {{requires template arguments; argument deduction not allowed in conversion function type}}
 
-  static A x; // expected-error {{declaration of variable 'x' with deduced type 'A' requires an initializer}}
+  static A x;
   static constexpr A y = 0;
 };
 
@@ -114,7 +114,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -127,7 +126,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,14 +5,13 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
 A f(0), g{}; // expected-error {{template arguments deduced as 'A' in declaration of 'f' and deduced as 'A' in declaration of 'g'}}
 
 struct B {
-  static A a; // expected-error {{requires an initializer}}
+  static A a;
 };
-extern A x; // expected-error {{requires an 

[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added a comment.

In https://reviews.llvm.org/D38216#924039, @lichray wrote:

> So gcc got this wrong?
>
>   https://wandbox.org/permlink/RVApvaca1ebUfInn


Yes, the declaration `extern A a;` in that example is ill-formed.


https://reviews.llvm.org/D38216



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[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Zhihao Yuan via Phabricator via cfe-commits]

lichray added a comment.

In https://reviews.llvm.org/D38216#923580, @rsmith wrote:

> That's almost right, but not all `extern` declarations are disallowed. (An 
> `extern` declaration is still a defining declaration if it has an 
> initializer.)


Good to know, thanks.

So gcc got this wrong?

https://wandbox.org/permlink/RVApvaca1ebUfInn


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[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Nicolas Lesser via Phabricator via cfe-commits]

Rakete updated this revision to Diff 122708.
Rakete added a comment.

Made `DeduceInits` empty instead of a workaround somewhere else. Is it still 
ok, @rsmith ?


https://reviews.llvm.org/D38216

Files:
  lib/Sema/SemaDecl.cpp
  test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
  test/Parser/cxx1z-class-template-argument-deduction.cpp


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -52,7 +52,7 @@
 
   operator A(); // expected-error {{requires template arguments; argument 
deduction not allowed in conversion function type}}
 
-  static A x; // expected-error {{declaration of variable 'x' with deduced 
type 'A' requires an initializer}}
+  static A x;
   static constexpr A y = 0;
 };
 
@@ -114,7 +114,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -127,7 +126,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' 
requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring 
variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are 
permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
@@ -13,6 +12,6 @@
 A f(0), g{}; // expected-error {{template arguments deduced as 'A' in 
declaration of 'f' and deduced as 'A' in declaration of 'g'}}
 
 struct B {
-  static A a; // expected-error {{requires an initializer}}
+  static A a;
 };
-extern A x; // expected-error {{requires an initializer}}
+extern A x;
Index: lib/Sema/SemaDecl.cpp
===
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10182,7 +10182,8 @@
   assert(Deduced && "deduceVarTypeFromInitializer for non-deduced type");
 
   // C++11 [dcl.spec.auto]p3
-  if (!Init) {
+  // Except for class argument deduction.
+  if (!Init && !isa(Deduced)) {
 assert(VDecl && "no init for init capture deduction?");
 Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
   << VDecl->getDeclName() << Type;
@@ -10189,7 +10190,10 @@
 return QualType();
   }
 
-  ArrayRef DeduceInits = Init;
+  ArrayRef DeduceInits;
+  if (Init)
+DeduceInits = Init;
+
   if (DirectInit) {
 if (auto *PL = dyn_cast_or_null(Init))
   DeduceInits = PL->exprs();


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -52,7 +52,7 @@
 
   operator A(); // expected-error {{requires template arguments; argument deduction not allowed in conversion function type}}
 
-  static A x; // expected-error {{declaration of variable 'x' with deduced type 'A' requires an initializer}}
+  static A x;
   static constexpr A y = 0;
 };
 
@@ -114,7 +114,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -127,7 +126,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
@@ -13,6 +12,6 @@
 A f(0), g{}; // expected-error {{template arguments deduced as 'A' in declaration of 'f' and deduced as 'A' in declaration of 'g'}}
 
 struct B {
-  static A a; // expected-error {{requires an 

[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added a comment.

In https://reviews.llvm.org/D38216#922768, @lichray wrote:

> So deducing from default initialization is indeed allowed, but `extern`
>  could be interpreted as outlawed because similar to the case of non-
>  inline static data member, where the declaration doesn't give **the**
>  initialization of that variable.  @rsmith, comments?


That's almost right, but not all `extern` declarations are disallowed. (An 
`extern` declaration is still a defining declaration if it has an initializer.)




Comment at: lib/Sema/SemaDecl.cpp:10208
+return DeduceTemplateSpecializationFromInitializer(
+  TSI, Entity, Kind, Init ? InitsCopy : MutableArrayRef());  
   }

Please put this `?:` expression into the declaration of `DeduceInits` instead 
of here. (We should build an empty list instead of a list of one null pointer 
when there is no init.)


https://reviews.llvm.org/D38216



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[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Zhihao Yuan via Phabricator via cfe-commits]

lichray added a comment.

In https://reviews.llvm.org/D38216#922709, @Rakete wrote:

> @lichray Isn't [dcl.type.auto.deduct] only for `auto` and `decltype(auto)`?


Sorry, reasoned on a confusingly similar part... Here is
updated information:

> 10.1.7.5 [dcl.type.class.deduct]
>  If a placeholder for a deduced class type appears as a decl-specifier in
>  the decl-specifier-seq of an initializing declaration (11.6) of a variable,
>  [...].



> 11.6 [dcl.init]/22
>  A declaration that specifies the initialization of a variable, whether from
>  an explicit initializer or by default initialization, is called the 
> initializing
>  declaration of that variable. [ Note: In most cases this is the defining
>  declaration (6.1) of the variable, but the initializing declaration of a non-
>  inline static data member (12.2.3.2) might be the declaration within the
>  class definition and not the definition at namespace scope. —end note ]

So deducing from default initialization is indeed allowed, but `extern`
could be interpreted as outlawed because similar to the case of non-
inline static data member, where the declaration doesn't give **the**
initialization of that variable.  @rsmith, comments?


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[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Nicolas Lesser via Phabricator via cfe-commits]

Rakete added a comment.

@lichray Isn't [dcl.type.auto.deduct] only for `auto` and `decltype(auto)`? 
Class template argument deduction is in [dcl.type.class.deduct], which doesn't 
seem to disallow declarations without an initializer.

About that `extern` business, yes that's indeed counter intuitive and weird. 
Couldn't find anything in the standard prohibiting this though, but I'm not so 
good at that either.


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[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Zhihao Yuan via Phabricator via cfe-commits]

lichray added a comment.

The standard hasn't allowed deducing any placeholder type without an 
initializer (10.1.7.4.1 [dcl.type.auto.deduct]/2) yet.

It's unclear to me what

  extern A x;

wants to archive.  Usually when people writing `extern` then expect an 
initializer to appear somewhere else, but with this declaration, defining

  A x = ...;

later may fail by resolving to a different type, which feels... interesting.


https://reviews.llvm.org/D38216



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[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Nicolas Lesser via Phabricator via cfe-commits]

Rakete updated this revision to Diff 122576.
Rakete added a comment.

Slight change + rebased + friendly ping :)


https://reviews.llvm.org/D38216

Files:
  lib/Sema/SemaDecl.cpp
  test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
  test/Parser/cxx1z-class-template-argument-deduction.cpp


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -52,7 +52,7 @@
 
   operator A(); // expected-error {{requires template arguments; argument 
deduction not allowed in conversion function type}}
 
-  static A x; // expected-error {{declaration of variable 'x' with deduced 
type 'A' requires an initializer}}
+  static A x;
   static constexpr A y = 0;
 };
 
@@ -114,7 +114,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -127,7 +126,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' 
requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring 
variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are 
permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
@@ -13,6 +12,6 @@
 A f(0), g{}; // expected-error {{template arguments deduced as 'A' in 
declaration of 'f' and deduced as 'A' in declaration of 'g'}}
 
 struct B {
-  static A a; // expected-error {{requires an initializer}}
+  static A a;
 };
-extern A x; // expected-error {{requires an initializer}}
+extern A x;
Index: lib/Sema/SemaDecl.cpp
===
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10182,7 +10182,8 @@
   assert(Deduced && "deduceVarTypeFromInitializer for non-deduced type");
 
   // C++11 [dcl.spec.auto]p3
-  if (!Init) {
+  // Except for class argument deduction.
+  if (!Init && !isa(Deduced)) {
 assert(VDecl && "no init for init capture deduction?");
 Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
   << VDecl->getDeclName() << Type;
@@ -10202,8 +10203,9 @@
 VDecl->getLocation(), DirectInit, Init);
 // FIXME: Initialization should not be taking a mutable list of inits. 
 SmallVector InitsCopy(DeduceInits.begin(), DeduceInits.end());
-return DeduceTemplateSpecializationFromInitializer(TSI, Entity, Kind,
-   InitsCopy);
+
+return DeduceTemplateSpecializationFromInitializer(
+  TSI, Entity, Kind, Init ? InitsCopy : MutableArrayRef());  
   }
 
   if (DirectInit) {


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -52,7 +52,7 @@
 
   operator A(); // expected-error {{requires template arguments; argument deduction not allowed in conversion function type}}
 
-  static A x; // expected-error {{declaration of variable 'x' with deduced type 'A' requires an initializer}}
+  static A x;
   static constexpr A y = 0;
 };
 
@@ -114,7 +114,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -127,7 +126,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};

[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Nicolas Lesser via Phabricator via cfe-commits]

Rakete updated this revision to Diff 119035.
Rakete added a comment.

Rebased and friendly ping :)


https://reviews.llvm.org/D38216

Files:
  lib/Sema/SemaDecl.cpp
  test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
  test/Parser/cxx1z-class-template-argument-deduction.cpp


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -52,7 +52,7 @@
 
   operator A(); // expected-error {{requires template arguments; argument 
deduction not allowed in conversion function type}}
 
-  static A x; // expected-error {{declaration of variable 'x' with deduced 
type 'A' requires an initializer}}
+  static A x;
   static constexpr A y = 0;
 };
 
@@ -114,7 +114,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -127,7 +126,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' 
requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring 
variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are 
permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
@@ -13,6 +12,6 @@
 A f(0), g{}; // expected-error {{template arguments deduced as 'A' in 
declaration of 'f' and deduced as 'A' in declaration of 'g'}}
 
 struct B {
-  static A a; // expected-error {{requires an initializer}}
+  static A a;
 };
-extern A x; // expected-error {{requires an initializer}}
+extern A x;
Index: lib/Sema/SemaDecl.cpp
===
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10174,7 +10174,8 @@
   assert(Deduced && "deduceVarTypeFromInitializer for non-deduced type");
 
   // C++11 [dcl.spec.auto]p3
-  if (!Init) {
+  // Except for class argument deduction.
+  if (!Init && !isa(Deduced)) {
 assert(VDecl && "no init for init capture deduction?");
 Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
   << VDecl->getDeclName() << Type;
@@ -10193,7 +10194,10 @@
 InitializationKind Kind = InitializationKind::CreateForInit(
 VDecl->getLocation(), DirectInit, Init);
 // FIXME: Initialization should not be taking a mutable list of inits. 
-SmallVector InitsCopy(DeduceInits.begin(), DeduceInits.end());
+SmallVector InitsCopy;
+if (Init)
+  InitsCopy = {DeduceInits.begin(), DeduceInits.end()};
+
 return DeduceTemplateSpecializationFromInitializer(TSI, Entity, Kind,
InitsCopy);
   }


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -52,7 +52,7 @@
 
   operator A(); // expected-error {{requires template arguments; argument deduction not allowed in conversion function type}}
 
-  static A x; // expected-error {{declaration of variable 'x' with deduced type 'A' requires an initializer}}
+  static A x;
   static constexpr A y = 0;
 };
 
@@ -114,7 +114,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -127,7 +126,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = 

[PATCH] D38216: [C++17] Fix class template argument deduction for default constructors without an initializer

[Nicolas Lesser via Phabricator via cfe-commits]

Rakete created this revision.
Rakete added a project: clang.

As the title says, this makes following code compile:

  template struct Foo {};
  Foo() -> Foo;
  
  Foo f; // ok


https://reviews.llvm.org/D38216

Files:
  lib/Sema/SemaDecl.cpp
  test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
  test/Parser/cxx1z-class-template-argument-deduction.cpp


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -52,7 +52,7 @@
 
   operator A(); // expected-error {{requires template arguments; argument 
deduction not allowed in conversion function type}}
 
-  static A x; // expected-error {{declaration of variable 'x' with deduced 
type 'A' requires an initializer}}
+  static A x;
   static constexpr A y = 0;
 };
 
@@ -114,7 +114,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -127,7 +126,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' 
requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring 
variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are 
permitted
-// FIXME: There isn't really a good reason to reject this.
-A b; // expected-error {{requires an initializer}}
+A b;
 A c [[]] {};
 
 A d = {}, e = {};
@@ -13,6 +12,6 @@
 A f(0), g{}; // expected-error {{template arguments deduced as 'A' in 
declaration of 'f' and deduced as 'A' in declaration of 'g'}}
 
 struct B {
-  static A a; // expected-error {{requires an initializer}}
+  static A a;
 };
-extern A x; // expected-error {{requires an initializer}}
+extern A x;
Index: lib/Sema/SemaDecl.cpp
===
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10091,7 +10091,8 @@
   assert(Deduced && "deduceVarTypeFromInitializer for non-deduced type");
 
   // C++11 [dcl.spec.auto]p3
-  if (!Init) {
+  // Except for class argument deduction.
+  if (!Init && !isa(Deduced)) {
 assert(VDecl && "no init for init capture deduction?");
 Diag(VDecl->getLocation(), diag::err_auto_var_requires_init)
   << VDecl->getDeclName() << Type;
@@ -10110,7 +10111,10 @@
 InitializationKind Kind = InitializationKind::CreateForInit(
 VDecl->getLocation(), DirectInit, Init);
 // FIXME: Initialization should not be taking a mutable list of inits. 
-SmallVector InitsCopy(DeduceInits.begin(), DeduceInits.end());
+SmallVector InitsCopy;
+if (Init)
+  InitsCopy = {DeduceInits.begin(), DeduceInits.end()};
+
 return DeduceTemplateSpecializationFromInitializer(TSI, Entity, Kind,
InitsCopy);
   }


Index: test/Parser/cxx1z-class-template-argument-deduction.cpp
===
--- test/Parser/cxx1z-class-template-argument-deduction.cpp
+++ test/Parser/cxx1z-class-template-argument-deduction.cpp
@@ -52,7 +52,7 @@
 
   operator A(); // expected-error {{requires template arguments; argument deduction not allowed in conversion function type}}
 
-  static A x; // expected-error {{declaration of variable 'x' with deduced type 'A' requires an initializer}}
+  static A x;
   static constexpr A y = 0;
 };
 
@@ -114,7 +114,6 @@
 (void)A{n};
 (void)new A(n);
 (void)new A{n};
-// FIXME: We should diagnose the lack of an initializer here.
 (void)new A;
   }
 }
@@ -127,7 +126,7 @@
 
   auto k() -> A; // expected-error{{requires template arguments}}
 
-  A a; // expected-error {{declaration of variable 'a' with deduced type 'A' requires an initializer}}
+  A a;
   A b = 0;
   const A c = 0;
   A (parens) = 0; // expected-error {{cannot use parentheses when declaring variable with deduced class template specialization type}}
Index: test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
===
--- test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.class.deduct/p1.cpp
@@ -5,8 +5,7 @@
 A(int) -> A;
 
 static constexpr inline const volatile A a = {}; // ok, specifiers are permitted
-// FIXME: There isn't really a good reason to reject this.
-A