c++: C++20 DR 2237, disallow simple-template-id in cdtor.

Message ID 20200404233053.1073028-1-polacek@redhat.com
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  • c++: C++20 DR 2237, disallow simple-template-id in cdtor.
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Patrick Palka via Gcc-patches April 4, 2020, 11:30 p.m.
This patch implements DR 2237 which says that a simple-template-id is
no longer valid as the declarator-id of a constructor or destructor;
see <https://eel.is/c++draft/diff.cpp17.class#2>.  It is not explicitly
stated but out-of-line destructors with a simple-template-id are also
meant to be ill-formed now.  (Out-of-line constructors like that are
invalid since DR1435 I think.)  This change only applies to C++20; it
is not a DR against C++17.

I'm not crazy about the diagnostic in constructors but ISTM that
cp_parser_constructor_declarator_p shouldn't print errors.

Does it seem reasonable to apply this now or should I defer to GCC 11?

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

2020-04-04  Marek Polacek  <polacek@redhat.com>

	DR 2237
	* parser.c (cp_parser_unqualified_id): Reject simple-template-id as
	the declarator-id of a destructor.
	(cp_parser_constructor_declarator_p): Reject simple-template-id as
	the declarator-id of a constructor.

	* g++.dg/DRs/dr2237.C: New test.
	* g++.dg/parse/constructor2.C: Add dg-error for C++20.
	* g++.dg/parse/dtor12.C: Likewise.
	* g++.dg/parse/dtor4.C: Likewise.
	* g++.dg/template/dtor4.C: Adjust dg-error.
	* g++.dg/template/error34.C: Likewise.
	* g++.old-deja/g++.other/inline15.C: Only run for C++17 and lesses.
	* g++.old-deja/g++.pt/ctor2.C: Add dg-error for C++20.
---
 gcc/cp/parser.c                                | 16 ++++++++++++++++
 gcc/testsuite/g++.dg/DRs/dr2237.C              | 18 ++++++++++++++++++
 gcc/testsuite/g++.dg/parse/constructor2.C      |  4 ++--
 gcc/testsuite/g++.dg/parse/dtor12.C            |  2 +-
 gcc/testsuite/g++.dg/parse/dtor4.C             |  2 +-
 gcc/testsuite/g++.dg/template/dtor4.C          |  2 +-
 gcc/testsuite/g++.dg/template/error34.C        | 10 +++++-----
 .../g++.old-deja/g++.other/inline15.C          |  2 +-
 gcc/testsuite/g++.old-deja/g++.pt/ctor2.C      |  2 +-
 9 files changed, 46 insertions(+), 12 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/DRs/dr2237.C


base-commit: 49a86fce1a879a206fb4b27f097910005d968fda
-- 
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA

Comments

Patrick Palka via Gcc-patches April 6, 2020, 1:46 a.m. | #1
On 4/4/20 7:30 PM, Marek Polacek wrote:
> This patch implements DR 2237 which says that a simple-template-id is

> no longer valid as the declarator-id of a constructor or destructor;

> see <https://eel.is/c++draft/diff.cpp17.class#2>.  It is not explicitly

> stated but out-of-line destructors with a simple-template-id are also

> meant to be ill-formed now.  (Out-of-line constructors like that are

> invalid since DR1435 I think.)  This change only applies to C++20; it

> is not a DR against C++17.

> 

> I'm not crazy about the diagnostic in constructors but ISTM that

> cp_parser_constructor_declarator_p shouldn't print errors.

> 

> Does it seem reasonable to apply this now or should I defer to GCC 11?


A new error should wait for GCC 11.

> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

> 

> 2020-04-04  Marek Polacek  <polacek@redhat.com>

> 

> 	DR 2237

> 	* parser.c (cp_parser_unqualified_id): Reject simple-template-id as

> 	the declarator-id of a destructor.

> 	(cp_parser_constructor_declarator_p): Reject simple-template-id as

> 	the declarator-id of a constructor.

> 

> 	* g++.dg/DRs/dr2237.C: New test.

> 	* g++.dg/parse/constructor2.C: Add dg-error for C++20.

> 	* g++.dg/parse/dtor12.C: Likewise.

> 	* g++.dg/parse/dtor4.C: Likewise.

> 	* g++.dg/template/dtor4.C: Adjust dg-error.

> 	* g++.dg/template/error34.C: Likewise.

> 	* g++.old-deja/g++.other/inline15.C: Only run for C++17 and lesses.

> 	* g++.old-deja/g++.pt/ctor2.C: Add dg-error for C++20.

> ---

>   gcc/cp/parser.c                                | 16 ++++++++++++++++

>   gcc/testsuite/g++.dg/DRs/dr2237.C              | 18 ++++++++++++++++++

>   gcc/testsuite/g++.dg/parse/constructor2.C      |  4 ++--

>   gcc/testsuite/g++.dg/parse/dtor12.C            |  2 +-

>   gcc/testsuite/g++.dg/parse/dtor4.C             |  2 +-

>   gcc/testsuite/g++.dg/template/dtor4.C          |  2 +-

>   gcc/testsuite/g++.dg/template/error34.C        | 10 +++++-----

>   .../g++.old-deja/g++.other/inline15.C          |  2 +-

>   gcc/testsuite/g++.old-deja/g++.pt/ctor2.C      |  2 +-

>   9 files changed, 46 insertions(+), 12 deletions(-)

>   create mode 100644 gcc/testsuite/g++.dg/DRs/dr2237.C

> 

> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c

> index 7e5921e039f..810edfa87a9 100644

> --- a/gcc/cp/parser.c

> +++ b/gcc/cp/parser.c

> @@ -6114,6 +6114,16 @@ cp_parser_unqualified_id (cp_parser* parser,

>   	    return build_min_nt_loc (loc, BIT_NOT_EXPR, make_auto ());

>   	  }

>   

> +	/* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

> +	   declarator-id of a constructor or destructor.  */

> +	if (token->type == CPP_TEMPLATE_ID && cxx_dialect >= cxx2a)

> +	  {

> +	    if (!cp_parser_uncommitted_to_tentative_parse_p (parser))

> +	      error_at (tilde_loc, "template-id not allowed for destructor");

> +	    cp_parser_simulate_error (parser);


The usual pattern is

if (!cp_parser_simulate_error (parser))
   error...

> +	    return error_mark_node;

> +	  }

> +

>   	/* If there was an explicit qualification (S::~T), first look

>   	   in the scope given by the qualification (i.e., S).

>   

> @@ -28675,6 +28685,12 @@ cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,

>         if (!constructor_name_p (id, nested_name_specifier))

>   	constructor_p = false;

>       }

> +  /* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

> +     declarator-id of a constructor or destructor.  */

> +  else if (constructor_p

> +	   && cxx_dialect >= cxx2a

> +	   && cp_lexer_next_token_is (parser->lexer, CPP_TEMPLATE_ID))

> +    constructor_p = false;

>     /* If we still think that this might be a constructor-declarator,

>        look for a class-name.  */

>     else if (constructor_p)


Do you also want to exclude CPP_TEMPLATE_ID from the test at the top of 
the function for C++20?

>   if (next_token->type != CPP_NAME

>       && next_token->type != CPP_SCOPE

>       && next_token->type != CPP_NESTED_NAME_SPECIFIER

>       && next_token->type != CPP_TEMPLATE_ID)

>     return false;


Jason
Patrick Palka via Gcc-patches May 11, 2020, 8:23 p.m. | #2
On Sun, Apr 05, 2020 at 09:46:09PM -0400, Jason Merrill wrote:
> On 4/4/20 7:30 PM, Marek Polacek wrote:

> > This patch implements DR 2237 which says that a simple-template-id is

> > no longer valid as the declarator-id of a constructor or destructor;

> > see <https://eel.is/c++draft/diff.cpp17.class#2>.  It is not explicitly

> > stated but out-of-line destructors with a simple-template-id are also

> > meant to be ill-formed now.  (Out-of-line constructors like that are

> > invalid since DR1435 I think.)  This change only applies to C++20; it

> > is not a DR against C++17.

> > 

> > I'm not crazy about the diagnostic in constructors but ISTM that

> > cp_parser_constructor_declarator_p shouldn't print errors.

> > 

> > Does it seem reasonable to apply this now or should I defer to GCC 11?

> 

> A new error should wait for GCC 11.


Coming back to this now that we're again in stage 1.

> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

> > 

> > 2020-04-04  Marek Polacek  <polacek@redhat.com>

> > 

> > 	DR 2237

> > 	* parser.c (cp_parser_unqualified_id): Reject simple-template-id as

> > 	the declarator-id of a destructor.

> > 	(cp_parser_constructor_declarator_p): Reject simple-template-id as

> > 	the declarator-id of a constructor.

> > 

> > 	* g++.dg/DRs/dr2237.C: New test.

> > 	* g++.dg/parse/constructor2.C: Add dg-error for C++20.

> > 	* g++.dg/parse/dtor12.C: Likewise.

> > 	* g++.dg/parse/dtor4.C: Likewise.

> > 	* g++.dg/template/dtor4.C: Adjust dg-error.

> > 	* g++.dg/template/error34.C: Likewise.

> > 	* g++.old-deja/g++.other/inline15.C: Only run for C++17 and lesses.

> > 	* g++.old-deja/g++.pt/ctor2.C: Add dg-error for C++20.

> > ---

> >   gcc/cp/parser.c                                | 16 ++++++++++++++++

> >   gcc/testsuite/g++.dg/DRs/dr2237.C              | 18 ++++++++++++++++++

> >   gcc/testsuite/g++.dg/parse/constructor2.C      |  4 ++--

> >   gcc/testsuite/g++.dg/parse/dtor12.C            |  2 +-

> >   gcc/testsuite/g++.dg/parse/dtor4.C             |  2 +-

> >   gcc/testsuite/g++.dg/template/dtor4.C          |  2 +-

> >   gcc/testsuite/g++.dg/template/error34.C        | 10 +++++-----

> >   .../g++.old-deja/g++.other/inline15.C          |  2 +-

> >   gcc/testsuite/g++.old-deja/g++.pt/ctor2.C      |  2 +-

> >   9 files changed, 46 insertions(+), 12 deletions(-)

> >   create mode 100644 gcc/testsuite/g++.dg/DRs/dr2237.C

> > 

> > diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c

> > index 7e5921e039f..810edfa87a9 100644

> > --- a/gcc/cp/parser.c

> > +++ b/gcc/cp/parser.c

> > @@ -6114,6 +6114,16 @@ cp_parser_unqualified_id (cp_parser* parser,

> >   	    return build_min_nt_loc (loc, BIT_NOT_EXPR, make_auto ());

> >   	  }

> > +	/* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

> > +	   declarator-id of a constructor or destructor.  */

> > +	if (token->type == CPP_TEMPLATE_ID && cxx_dialect >= cxx2a)

> > +	  {

> > +	    if (!cp_parser_uncommitted_to_tentative_parse_p (parser))

> > +	      error_at (tilde_loc, "template-id not allowed for destructor");

> > +	    cp_parser_simulate_error (parser);

> 

> The usual pattern is

> 

> if (!cp_parser_simulate_error (parser))

>   error...


Fixed.

> > +	    return error_mark_node;

> > +	  }

> > +

> >   	/* If there was an explicit qualification (S::~T), first look

> >   	   in the scope given by the qualification (i.e., S).

> > @@ -28675,6 +28685,12 @@ cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,

> >         if (!constructor_name_p (id, nested_name_specifier))

> >   	constructor_p = false;

> >       }

> > +  /* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

> > +     declarator-id of a constructor or destructor.  */

> > +  else if (constructor_p

> > +	   && cxx_dialect >= cxx2a

> > +	   && cp_lexer_next_token_is (parser->lexer, CPP_TEMPLATE_ID))

> > +    constructor_p = false;

> >     /* If we still think that this might be a constructor-declarator,

> >        look for a class-name.  */

> >     else if (constructor_p)

> 

> Do you also want to exclude CPP_TEMPLATE_ID from the test at the top of the

> function for C++20?


In fact we can get away with only excluding CPP_TEMPLATE_ID in C++20 there,
because for e.g. X<T>::X<T>(); we'll give the "names the constructor, not the
type" error, so we won't even get here.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

-- >8 --
This patch implements DR 2237 which says that a simple-template-id is
no longer valid as the declarator-id of a constructor or destructor;
see [diff.cpp17.class]#2.  It is not explicitly stated but out-of-line
destructors with a simple-template-id are also meant to be ill-formed
now.  (Out-of-line constructors like that are invalid since DR1435 I
think.)  This change only applies to C++20; it is not a DR against C++17.

I'm not crazy about the diagnostic in constructors but ISTM that
cp_parser_constructor_declarator_p shouldn't print errors.

	DR 2237
	* parser.c (cp_parser_unqualified_id): Reject simple-template-id as
	the declarator-id of a destructor.
	(cp_parser_constructor_declarator_p): Reject simple-template-id as
	the declarator-id of a constructor.

	* g++.dg/DRs/dr2237.C: New test.
	* g++.dg/parse/constructor2.C: Add dg-error for C++20.
	* g++.dg/parse/dtor12.C: Likewise.
	* g++.dg/parse/dtor4.C: Likewise.
	* g++.dg/template/dtor4.C: Adjust dg-error.
	* g++.dg/template/error34.C: Likewise.
	* g++.old-deja/g++.other/inline15.C: Only run for C++17 and lesses.
	* g++.old-deja/g++.pt/ctor2.C: Add dg-error for C++20.
---
 gcc/cp/parser.c                                | 13 ++++++++++++-
 gcc/testsuite/g++.dg/DRs/dr2237.C              | 18 ++++++++++++++++++
 gcc/testsuite/g++.dg/parse/constructor2.C      |  4 ++--
 gcc/testsuite/g++.dg/parse/dtor12.C            |  2 +-
 gcc/testsuite/g++.dg/parse/dtor4.C             |  2 +-
 gcc/testsuite/g++.dg/template/dtor4.C          |  2 +-
 gcc/testsuite/g++.dg/template/error34.C        | 10 +++++-----
 .../g++.old-deja/g++.other/inline15.C          |  2 +-
 gcc/testsuite/g++.old-deja/g++.pt/ctor2.C      |  2 +-
 9 files changed, 42 insertions(+), 13 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/DRs/dr2237.C

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 591f44f4934..593c45b5888 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -6114,6 +6114,15 @@ cp_parser_unqualified_id (cp_parser* parser,
 	    return build_min_nt_loc (loc, BIT_NOT_EXPR, make_auto ());
 	  }
 
+	/* DR 2237 (C++20 only): A simple-template-id is no longer valid as the
+	   declarator-id of a constructor or destructor.  */
+	if (token->type == CPP_TEMPLATE_ID && cxx_dialect >= cxx2a)
+	  {
+	    if (!cp_parser_simulate_error (parser))
+	      error_at (tilde_loc, "template-id not allowed for destructor");
+	    return error_mark_node;
+	  }
+
 	/* If there was an explicit qualification (S::~T), first look
 	   in the scope given by the qualification (i.e., S).
 
@@ -28636,7 +28645,9 @@ cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,
   if (next_token->type != CPP_NAME
       && next_token->type != CPP_SCOPE
       && next_token->type != CPP_NESTED_NAME_SPECIFIER
-      && next_token->type != CPP_TEMPLATE_ID)
+      /* DR 2237 (C++20 only): A simple-template-id is no longer valid as the
+	 declarator-id of a constructor or destructor.  */
+      && (next_token->type != CPP_TEMPLATE_ID || cxx_dialect >= cxx2a))
     return false;
 
   /* Parse tentatively; we are going to roll back all of the tokens
diff --git a/gcc/testsuite/g++.dg/DRs/dr2237.C b/gcc/testsuite/g++.dg/DRs/dr2237.C
new file mode 100644
index 00000000000..17abdf179c1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/DRs/dr2237.C
@@ -0,0 +1,18 @@
+// DR 2237 - Can a template-id name a constructor?
+
+template<class T>
+struct X {
+  X<T>(); // { dg-error "expected" "" { target c++2a } }
+  X(int); // OK, injected-class-name used
+  ~X<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }
+};
+
+// ill-formed since DR1435
+template<typename T> X<T>::X<T>() {} // { dg-error "names the constructor|as no template constructors" }
+template<typename T> X<T>::~X<T>() {} // { dg-error "template-id not allowed for destructor" "" { target c++2a } }
+
+struct Q {
+  // ill-formed since DR1435
+  template<typename T> friend X<T>::X<T>(); // { dg-error "names the constructor|as no template constructors" }
+  template<typename T> friend X<T>::~X<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }
+};
diff --git a/gcc/testsuite/g++.dg/parse/constructor2.C b/gcc/testsuite/g++.dg/parse/constructor2.C
index e514e9397e9..87007e9c715 100644
--- a/gcc/testsuite/g++.dg/parse/constructor2.C
+++ b/gcc/testsuite/g++.dg/parse/constructor2.C
@@ -5,7 +5,7 @@ class T
 { 
 public: 
   T(short,short f=0) {} 
-  T<TClass>(int f) {} 
-  T<TClass>(int f=0,const char* b=0) {} 
+  T<TClass>(int f) {} // { dg-error "expected" "" { target c++2a } }
+  T<TClass>(int f=0,const char* b=0) {} // { dg-error "expected" "" { target c++2a } }
 }; 
 
diff --git a/gcc/testsuite/g++.dg/parse/dtor12.C b/gcc/testsuite/g++.dg/parse/dtor12.C
index 1acdfa36b69..d758d3e861d 100644
--- a/gcc/testsuite/g++.dg/parse/dtor12.C
+++ b/gcc/testsuite/g++.dg/parse/dtor12.C
@@ -2,5 +2,5 @@
 
 template <class T> class a
 {
-  ~a<T>();
+  ~a<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }
 };
diff --git a/gcc/testsuite/g++.dg/parse/dtor4.C b/gcc/testsuite/g++.dg/parse/dtor4.C
index 729ee2fa130..1059c189eff 100644
--- a/gcc/testsuite/g++.dg/parse/dtor4.C
+++ b/gcc/testsuite/g++.dg/parse/dtor4.C
@@ -7,4 +7,4 @@ template <int N> struct X {
 };
 
 template <int N>
-X<N>::~X<N>(){}
+X<N>::~X<N>(){} // { dg-error "template-id not allowed for destructor" "" { target c++2a } }
diff --git a/gcc/testsuite/g++.dg/template/dtor4.C b/gcc/testsuite/g++.dg/template/dtor4.C
index 4f277b248bd..917681fc13e 100644
--- a/gcc/testsuite/g++.dg/template/dtor4.C
+++ b/gcc/testsuite/g++.dg/template/dtor4.C
@@ -5,5 +5,5 @@
 
 template<int> struct A
 {
-  ~A<0>(); // { dg-error "parse error|declaration" }
+  ~A<0>(); // { dg-error "parse error|declaration|template-id" }
 };
diff --git a/gcc/testsuite/g++.dg/template/error34.C b/gcc/testsuite/g++.dg/template/error34.C
index d0cbcaef28e..ab688d9ba8c 100644
--- a/gcc/testsuite/g++.dg/template/error34.C
+++ b/gcc/testsuite/g++.dg/template/error34.C
@@ -3,27 +3,27 @@
 
 template<typename T> struct A
 {
-  A<__builtin_offsetof(T, x)>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\)" }
+  A<__builtin_offsetof(T, x)>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\)|expected" }
 };
 
 template<typename T> struct B
 {
-  B<__builtin_offsetof(T, x.y)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\)" }
+  B<__builtin_offsetof(T, x.y)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\)|expected" }
 };
 
 template<typename T> struct C
 {
-  C<__builtin_offsetof(T, x[6])>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\\[6\\\]\\)" }
+  C<__builtin_offsetof(T, x[6])>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\\[6\\\]\\)|expected" }
 };
 
 template<typename T> struct D
 {
-  D<__builtin_offsetof(T, x.y[6].z)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\\[6\\\].z\\)" }
+  D<__builtin_offsetof(T, x.y[6].z)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\\[6\\\].z\\)|expected" }
 };
 
 struct E { int x; };
 
 template<typename T> struct F
 {
-  F<__builtin_offsetof(E, x)>();	// { dg-error "type/value mismatch|offsetof\\(E, x\\)" }
+  F<__builtin_offsetof(E, x)>();	// { dg-error "type/value mismatch|offsetof\\(E, x\\)|expected" }
 };
diff --git a/gcc/testsuite/g++.old-deja/g++.other/inline15.C b/gcc/testsuite/g++.old-deja/g++.other/inline15.C
index 43f7f5e3025..a31c60960a5 100644
--- a/gcc/testsuite/g++.old-deja/g++.other/inline15.C
+++ b/gcc/testsuite/g++.old-deja/g++.other/inline15.C
@@ -1,4 +1,4 @@
-// { dg-do assemble  }
+// { dg-do assemble { target c++17_down } }
 // { dg-options "-O1" }
 // Origin: Jakub Jelinek <jakub@redhat.com>
 
diff --git a/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C b/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C
index a8be91ddbb9..4159c84ff56 100644
--- a/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C
+++ b/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C
@@ -4,7 +4,7 @@
 
 template <class T>
 struct A {
-  A<T>();
+  A<T>(); // { dg-error "expected" "" { target c++2a } }
 };
 
 template <class T>

base-commit: 2b2d298ff845ab7a07ffbd51da79473736da3324
-- 
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA
Patrick Palka via Gcc-patches May 20, 2020, 6:05 p.m. | #3
Ping.

On Mon, May 11, 2020 at 04:23:17PM -0400, Marek Polacek via Gcc-patches wrote:
> On Sun, Apr 05, 2020 at 09:46:09PM -0400, Jason Merrill wrote:

> > On 4/4/20 7:30 PM, Marek Polacek wrote:

> > > This patch implements DR 2237 which says that a simple-template-id is

> > > no longer valid as the declarator-id of a constructor or destructor;

> > > see <https://eel.is/c++draft/diff.cpp17.class#2>.  It is not explicitly

> > > stated but out-of-line destructors with a simple-template-id are also

> > > meant to be ill-formed now.  (Out-of-line constructors like that are

> > > invalid since DR1435 I think.)  This change only applies to C++20; it

> > > is not a DR against C++17.

> > > 

> > > I'm not crazy about the diagnostic in constructors but ISTM that

> > > cp_parser_constructor_declarator_p shouldn't print errors.

> > > 

> > > Does it seem reasonable to apply this now or should I defer to GCC 11?

> > 

> > A new error should wait for GCC 11.

> 

> Coming back to this now that we're again in stage 1.

> 

> > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

> > > 

> > > 2020-04-04  Marek Polacek  <polacek@redhat.com>

> > > 

> > > 	DR 2237

> > > 	* parser.c (cp_parser_unqualified_id): Reject simple-template-id as

> > > 	the declarator-id of a destructor.

> > > 	(cp_parser_constructor_declarator_p): Reject simple-template-id as

> > > 	the declarator-id of a constructor.

> > > 

> > > 	* g++.dg/DRs/dr2237.C: New test.

> > > 	* g++.dg/parse/constructor2.C: Add dg-error for C++20.

> > > 	* g++.dg/parse/dtor12.C: Likewise.

> > > 	* g++.dg/parse/dtor4.C: Likewise.

> > > 	* g++.dg/template/dtor4.C: Adjust dg-error.

> > > 	* g++.dg/template/error34.C: Likewise.

> > > 	* g++.old-deja/g++.other/inline15.C: Only run for C++17 and lesses.

> > > 	* g++.old-deja/g++.pt/ctor2.C: Add dg-error for C++20.

> > > ---

> > >   gcc/cp/parser.c                                | 16 ++++++++++++++++

> > >   gcc/testsuite/g++.dg/DRs/dr2237.C              | 18 ++++++++++++++++++

> > >   gcc/testsuite/g++.dg/parse/constructor2.C      |  4 ++--

> > >   gcc/testsuite/g++.dg/parse/dtor12.C            |  2 +-

> > >   gcc/testsuite/g++.dg/parse/dtor4.C             |  2 +-

> > >   gcc/testsuite/g++.dg/template/dtor4.C          |  2 +-

> > >   gcc/testsuite/g++.dg/template/error34.C        | 10 +++++-----

> > >   .../g++.old-deja/g++.other/inline15.C          |  2 +-

> > >   gcc/testsuite/g++.old-deja/g++.pt/ctor2.C      |  2 +-

> > >   9 files changed, 46 insertions(+), 12 deletions(-)

> > >   create mode 100644 gcc/testsuite/g++.dg/DRs/dr2237.C

> > > 

> > > diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c

> > > index 7e5921e039f..810edfa87a9 100644

> > > --- a/gcc/cp/parser.c

> > > +++ b/gcc/cp/parser.c

> > > @@ -6114,6 +6114,16 @@ cp_parser_unqualified_id (cp_parser* parser,

> > >   	    return build_min_nt_loc (loc, BIT_NOT_EXPR, make_auto ());

> > >   	  }

> > > +	/* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

> > > +	   declarator-id of a constructor or destructor.  */

> > > +	if (token->type == CPP_TEMPLATE_ID && cxx_dialect >= cxx2a)

> > > +	  {

> > > +	    if (!cp_parser_uncommitted_to_tentative_parse_p (parser))

> > > +	      error_at (tilde_loc, "template-id not allowed for destructor");

> > > +	    cp_parser_simulate_error (parser);

> > 

> > The usual pattern is

> > 

> > if (!cp_parser_simulate_error (parser))

> >   error...

> 

> Fixed.

> 

> > > +	    return error_mark_node;

> > > +	  }

> > > +

> > >   	/* If there was an explicit qualification (S::~T), first look

> > >   	   in the scope given by the qualification (i.e., S).

> > > @@ -28675,6 +28685,12 @@ cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,

> > >         if (!constructor_name_p (id, nested_name_specifier))

> > >   	constructor_p = false;

> > >       }

> > > +  /* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

> > > +     declarator-id of a constructor or destructor.  */

> > > +  else if (constructor_p

> > > +	   && cxx_dialect >= cxx2a

> > > +	   && cp_lexer_next_token_is (parser->lexer, CPP_TEMPLATE_ID))

> > > +    constructor_p = false;

> > >     /* If we still think that this might be a constructor-declarator,

> > >        look for a class-name.  */

> > >     else if (constructor_p)

> > 

> > Do you also want to exclude CPP_TEMPLATE_ID from the test at the top of the

> > function for C++20?

> 

> In fact we can get away with only excluding CPP_TEMPLATE_ID in C++20 there,

> because for e.g. X<T>::X<T>(); we'll give the "names the constructor, not the

> type" error, so we won't even get here.

> 

> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

> 

> -- >8 --

> This patch implements DR 2237 which says that a simple-template-id is

> no longer valid as the declarator-id of a constructor or destructor;

> see [diff.cpp17.class]#2.  It is not explicitly stated but out-of-line

> destructors with a simple-template-id are also meant to be ill-formed

> now.  (Out-of-line constructors like that are invalid since DR1435 I

> think.)  This change only applies to C++20; it is not a DR against C++17.

> 

> I'm not crazy about the diagnostic in constructors but ISTM that

> cp_parser_constructor_declarator_p shouldn't print errors.

> 

> 	DR 2237

> 	* parser.c (cp_parser_unqualified_id): Reject simple-template-id as

> 	the declarator-id of a destructor.

> 	(cp_parser_constructor_declarator_p): Reject simple-template-id as

> 	the declarator-id of a constructor.

> 

> 	* g++.dg/DRs/dr2237.C: New test.

> 	* g++.dg/parse/constructor2.C: Add dg-error for C++20.

> 	* g++.dg/parse/dtor12.C: Likewise.

> 	* g++.dg/parse/dtor4.C: Likewise.

> 	* g++.dg/template/dtor4.C: Adjust dg-error.

> 	* g++.dg/template/error34.C: Likewise.

> 	* g++.old-deja/g++.other/inline15.C: Only run for C++17 and lesses.

> 	* g++.old-deja/g++.pt/ctor2.C: Add dg-error for C++20.

> ---

>  gcc/cp/parser.c                                | 13 ++++++++++++-

>  gcc/testsuite/g++.dg/DRs/dr2237.C              | 18 ++++++++++++++++++

>  gcc/testsuite/g++.dg/parse/constructor2.C      |  4 ++--

>  gcc/testsuite/g++.dg/parse/dtor12.C            |  2 +-

>  gcc/testsuite/g++.dg/parse/dtor4.C             |  2 +-

>  gcc/testsuite/g++.dg/template/dtor4.C          |  2 +-

>  gcc/testsuite/g++.dg/template/error34.C        | 10 +++++-----

>  .../g++.old-deja/g++.other/inline15.C          |  2 +-

>  gcc/testsuite/g++.old-deja/g++.pt/ctor2.C      |  2 +-

>  9 files changed, 42 insertions(+), 13 deletions(-)

>  create mode 100644 gcc/testsuite/g++.dg/DRs/dr2237.C

> 

> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c

> index 591f44f4934..593c45b5888 100644

> --- a/gcc/cp/parser.c

> +++ b/gcc/cp/parser.c

> @@ -6114,6 +6114,15 @@ cp_parser_unqualified_id (cp_parser* parser,

>  	    return build_min_nt_loc (loc, BIT_NOT_EXPR, make_auto ());

>  	  }

>  

> +	/* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

> +	   declarator-id of a constructor or destructor.  */

> +	if (token->type == CPP_TEMPLATE_ID && cxx_dialect >= cxx2a)

> +	  {

> +	    if (!cp_parser_simulate_error (parser))

> +	      error_at (tilde_loc, "template-id not allowed for destructor");

> +	    return error_mark_node;

> +	  }

> +

>  	/* If there was an explicit qualification (S::~T), first look

>  	   in the scope given by the qualification (i.e., S).

>  

> @@ -28636,7 +28645,9 @@ cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,

>    if (next_token->type != CPP_NAME

>        && next_token->type != CPP_SCOPE

>        && next_token->type != CPP_NESTED_NAME_SPECIFIER

> -      && next_token->type != CPP_TEMPLATE_ID)

> +      /* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

> +	 declarator-id of a constructor or destructor.  */

> +      && (next_token->type != CPP_TEMPLATE_ID || cxx_dialect >= cxx2a))

>      return false;

>  

>    /* Parse tentatively; we are going to roll back all of the tokens

> diff --git a/gcc/testsuite/g++.dg/DRs/dr2237.C b/gcc/testsuite/g++.dg/DRs/dr2237.C

> new file mode 100644

> index 00000000000..17abdf179c1

> --- /dev/null

> +++ b/gcc/testsuite/g++.dg/DRs/dr2237.C

> @@ -0,0 +1,18 @@

> +// DR 2237 - Can a template-id name a constructor?

> +

> +template<class T>

> +struct X {

> +  X<T>(); // { dg-error "expected" "" { target c++2a } }

> +  X(int); // OK, injected-class-name used

> +  ~X<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }

> +};

> +

> +// ill-formed since DR1435

> +template<typename T> X<T>::X<T>() {} // { dg-error "names the constructor|as no template constructors" }

> +template<typename T> X<T>::~X<T>() {} // { dg-error "template-id not allowed for destructor" "" { target c++2a } }

> +

> +struct Q {

> +  // ill-formed since DR1435

> +  template<typename T> friend X<T>::X<T>(); // { dg-error "names the constructor|as no template constructors" }

> +  template<typename T> friend X<T>::~X<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }

> +};

> diff --git a/gcc/testsuite/g++.dg/parse/constructor2.C b/gcc/testsuite/g++.dg/parse/constructor2.C

> index e514e9397e9..87007e9c715 100644

> --- a/gcc/testsuite/g++.dg/parse/constructor2.C

> +++ b/gcc/testsuite/g++.dg/parse/constructor2.C

> @@ -5,7 +5,7 @@ class T

>  { 

>  public: 

>    T(short,short f=0) {} 

> -  T<TClass>(int f) {} 

> -  T<TClass>(int f=0,const char* b=0) {} 

> +  T<TClass>(int f) {} // { dg-error "expected" "" { target c++2a } }

> +  T<TClass>(int f=0,const char* b=0) {} // { dg-error "expected" "" { target c++2a } }

>  }; 

>  

> diff --git a/gcc/testsuite/g++.dg/parse/dtor12.C b/gcc/testsuite/g++.dg/parse/dtor12.C

> index 1acdfa36b69..d758d3e861d 100644

> --- a/gcc/testsuite/g++.dg/parse/dtor12.C

> +++ b/gcc/testsuite/g++.dg/parse/dtor12.C

> @@ -2,5 +2,5 @@

>  

>  template <class T> class a

>  {

> -  ~a<T>();

> +  ~a<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }

>  };

> diff --git a/gcc/testsuite/g++.dg/parse/dtor4.C b/gcc/testsuite/g++.dg/parse/dtor4.C

> index 729ee2fa130..1059c189eff 100644

> --- a/gcc/testsuite/g++.dg/parse/dtor4.C

> +++ b/gcc/testsuite/g++.dg/parse/dtor4.C

> @@ -7,4 +7,4 @@ template <int N> struct X {

>  };

>  

>  template <int N>

> -X<N>::~X<N>(){}

> +X<N>::~X<N>(){} // { dg-error "template-id not allowed for destructor" "" { target c++2a } }

> diff --git a/gcc/testsuite/g++.dg/template/dtor4.C b/gcc/testsuite/g++.dg/template/dtor4.C

> index 4f277b248bd..917681fc13e 100644

> --- a/gcc/testsuite/g++.dg/template/dtor4.C

> +++ b/gcc/testsuite/g++.dg/template/dtor4.C

> @@ -5,5 +5,5 @@

>  

>  template<int> struct A

>  {

> -  ~A<0>(); // { dg-error "parse error|declaration" }

> +  ~A<0>(); // { dg-error "parse error|declaration|template-id" }

>  };

> diff --git a/gcc/testsuite/g++.dg/template/error34.C b/gcc/testsuite/g++.dg/template/error34.C

> index d0cbcaef28e..ab688d9ba8c 100644

> --- a/gcc/testsuite/g++.dg/template/error34.C

> +++ b/gcc/testsuite/g++.dg/template/error34.C

> @@ -3,27 +3,27 @@

>  

>  template<typename T> struct A

>  {

> -  A<__builtin_offsetof(T, x)>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\)" }

> +  A<__builtin_offsetof(T, x)>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\)|expected" }

>  };

>  

>  template<typename T> struct B

>  {

> -  B<__builtin_offsetof(T, x.y)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\)" }

> +  B<__builtin_offsetof(T, x.y)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\)|expected" }

>  };

>  

>  template<typename T> struct C

>  {

> -  C<__builtin_offsetof(T, x[6])>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\\[6\\\]\\)" }

> +  C<__builtin_offsetof(T, x[6])>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\\[6\\\]\\)|expected" }

>  };

>  

>  template<typename T> struct D

>  {

> -  D<__builtin_offsetof(T, x.y[6].z)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\\[6\\\].z\\)" }

> +  D<__builtin_offsetof(T, x.y[6].z)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\\[6\\\].z\\)|expected" }

>  };

>  

>  struct E { int x; };

>  

>  template<typename T> struct F

>  {

> -  F<__builtin_offsetof(E, x)>();	// { dg-error "type/value mismatch|offsetof\\(E, x\\)" }

> +  F<__builtin_offsetof(E, x)>();	// { dg-error "type/value mismatch|offsetof\\(E, x\\)|expected" }

>  };

> diff --git a/gcc/testsuite/g++.old-deja/g++.other/inline15.C b/gcc/testsuite/g++.old-deja/g++.other/inline15.C

> index 43f7f5e3025..a31c60960a5 100644

> --- a/gcc/testsuite/g++.old-deja/g++.other/inline15.C

> +++ b/gcc/testsuite/g++.old-deja/g++.other/inline15.C

> @@ -1,4 +1,4 @@

> -// { dg-do assemble  }

> +// { dg-do assemble { target c++17_down } }

>  // { dg-options "-O1" }

>  // Origin: Jakub Jelinek <jakub@redhat.com>

>  

> diff --git a/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C b/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C

> index a8be91ddbb9..4159c84ff56 100644

> --- a/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C

> +++ b/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C

> @@ -4,7 +4,7 @@

>  

>  template <class T>

>  struct A {

> -  A<T>();

> +  A<T>(); // { dg-error "expected" "" { target c++2a } }

>  };

>  

>  template <class T>

> 

> base-commit: 2b2d298ff845ab7a07ffbd51da79473736da3324

> -- 

> Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA

> 


Marek
Patrick Palka via Gcc-patches May 20, 2020, 8:45 p.m. | #4
On 5/20/20 2:05 PM, Marek Polacek wrote:
> Ping.


OK (with 2a->20, of course).

Jason


> On Mon, May 11, 2020 at 04:23:17PM -0400, Marek Polacek via Gcc-patches wrote:

>> On Sun, Apr 05, 2020 at 09:46:09PM -0400, Jason Merrill wrote:

>>> On 4/4/20 7:30 PM, Marek Polacek wrote:

>>>> This patch implements DR 2237 which says that a simple-template-id is

>>>> no longer valid as the declarator-id of a constructor or destructor;

>>>> see <https://eel.is/c++draft/diff.cpp17.class#2>.  It is not explicitly

>>>> stated but out-of-line destructors with a simple-template-id are also

>>>> meant to be ill-formed now.  (Out-of-line constructors like that are

>>>> invalid since DR1435 I think.)  This change only applies to C++20; it

>>>> is not a DR against C++17.

>>>>

>>>> I'm not crazy about the diagnostic in constructors but ISTM that

>>>> cp_parser_constructor_declarator_p shouldn't print errors.

>>>>

>>>> Does it seem reasonable to apply this now or should I defer to GCC 11?

>>>

>>> A new error should wait for GCC 11.

>>

>> Coming back to this now that we're again in stage 1.

>>

>>>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

>>>>

>>>> 2020-04-04  Marek Polacek  <polacek@redhat.com>

>>>>

>>>> 	DR 2237

>>>> 	* parser.c (cp_parser_unqualified_id): Reject simple-template-id as

>>>> 	the declarator-id of a destructor.

>>>> 	(cp_parser_constructor_declarator_p): Reject simple-template-id as

>>>> 	the declarator-id of a constructor.

>>>>

>>>> 	* g++.dg/DRs/dr2237.C: New test.

>>>> 	* g++.dg/parse/constructor2.C: Add dg-error for C++20.

>>>> 	* g++.dg/parse/dtor12.C: Likewise.

>>>> 	* g++.dg/parse/dtor4.C: Likewise.

>>>> 	* g++.dg/template/dtor4.C: Adjust dg-error.

>>>> 	* g++.dg/template/error34.C: Likewise.

>>>> 	* g++.old-deja/g++.other/inline15.C: Only run for C++17 and lesses.

>>>> 	* g++.old-deja/g++.pt/ctor2.C: Add dg-error for C++20.

>>>> ---

>>>>    gcc/cp/parser.c                                | 16 ++++++++++++++++

>>>>    gcc/testsuite/g++.dg/DRs/dr2237.C              | 18 ++++++++++++++++++

>>>>    gcc/testsuite/g++.dg/parse/constructor2.C      |  4 ++--

>>>>    gcc/testsuite/g++.dg/parse/dtor12.C            |  2 +-

>>>>    gcc/testsuite/g++.dg/parse/dtor4.C             |  2 +-

>>>>    gcc/testsuite/g++.dg/template/dtor4.C          |  2 +-

>>>>    gcc/testsuite/g++.dg/template/error34.C        | 10 +++++-----

>>>>    .../g++.old-deja/g++.other/inline15.C          |  2 +-

>>>>    gcc/testsuite/g++.old-deja/g++.pt/ctor2.C      |  2 +-

>>>>    9 files changed, 46 insertions(+), 12 deletions(-)

>>>>    create mode 100644 gcc/testsuite/g++.dg/DRs/dr2237.C

>>>>

>>>> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c

>>>> index 7e5921e039f..810edfa87a9 100644

>>>> --- a/gcc/cp/parser.c

>>>> +++ b/gcc/cp/parser.c

>>>> @@ -6114,6 +6114,16 @@ cp_parser_unqualified_id (cp_parser* parser,

>>>>    	    return build_min_nt_loc (loc, BIT_NOT_EXPR, make_auto ());

>>>>    	  }

>>>> +	/* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

>>>> +	   declarator-id of a constructor or destructor.  */

>>>> +	if (token->type == CPP_TEMPLATE_ID && cxx_dialect >= cxx2a)

>>>> +	  {

>>>> +	    if (!cp_parser_uncommitted_to_tentative_parse_p (parser))

>>>> +	      error_at (tilde_loc, "template-id not allowed for destructor");

>>>> +	    cp_parser_simulate_error (parser);

>>>

>>> The usual pattern is

>>>

>>> if (!cp_parser_simulate_error (parser))

>>>    error...

>>

>> Fixed.

>>

>>>> +	    return error_mark_node;

>>>> +	  }

>>>> +

>>>>    	/* If there was an explicit qualification (S::~T), first look

>>>>    	   in the scope given by the qualification (i.e., S).

>>>> @@ -28675,6 +28685,12 @@ cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,

>>>>          if (!constructor_name_p (id, nested_name_specifier))

>>>>    	constructor_p = false;

>>>>        }

>>>> +  /* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

>>>> +     declarator-id of a constructor or destructor.  */

>>>> +  else if (constructor_p

>>>> +	   && cxx_dialect >= cxx2a

>>>> +	   && cp_lexer_next_token_is (parser->lexer, CPP_TEMPLATE_ID))

>>>> +    constructor_p = false;

>>>>      /* If we still think that this might be a constructor-declarator,

>>>>         look for a class-name.  */

>>>>      else if (constructor_p)

>>>

>>> Do you also want to exclude CPP_TEMPLATE_ID from the test at the top of the

>>> function for C++20?

>>

>> In fact we can get away with only excluding CPP_TEMPLATE_ID in C++20 there,

>> because for e.g. X<T>::X<T>(); we'll give the "names the constructor, not the

>> type" error, so we won't even get here.

>>

>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

>>

>> -- >8 --

>> This patch implements DR 2237 which says that a simple-template-id is

>> no longer valid as the declarator-id of a constructor or destructor;

>> see [diff.cpp17.class]#2.  It is not explicitly stated but out-of-line

>> destructors with a simple-template-id are also meant to be ill-formed

>> now.  (Out-of-line constructors like that are invalid since DR1435 I

>> think.)  This change only applies to C++20; it is not a DR against C++17.

>>

>> I'm not crazy about the diagnostic in constructors but ISTM that

>> cp_parser_constructor_declarator_p shouldn't print errors.

>>

>> 	DR 2237

>> 	* parser.c (cp_parser_unqualified_id): Reject simple-template-id as

>> 	the declarator-id of a destructor.

>> 	(cp_parser_constructor_declarator_p): Reject simple-template-id as

>> 	the declarator-id of a constructor.

>>

>> 	* g++.dg/DRs/dr2237.C: New test.

>> 	* g++.dg/parse/constructor2.C: Add dg-error for C++20.

>> 	* g++.dg/parse/dtor12.C: Likewise.

>> 	* g++.dg/parse/dtor4.C: Likewise.

>> 	* g++.dg/template/dtor4.C: Adjust dg-error.

>> 	* g++.dg/template/error34.C: Likewise.

>> 	* g++.old-deja/g++.other/inline15.C: Only run for C++17 and lesses.

>> 	* g++.old-deja/g++.pt/ctor2.C: Add dg-error for C++20.

>> ---

>>   gcc/cp/parser.c                                | 13 ++++++++++++-

>>   gcc/testsuite/g++.dg/DRs/dr2237.C              | 18 ++++++++++++++++++

>>   gcc/testsuite/g++.dg/parse/constructor2.C      |  4 ++--

>>   gcc/testsuite/g++.dg/parse/dtor12.C            |  2 +-

>>   gcc/testsuite/g++.dg/parse/dtor4.C             |  2 +-

>>   gcc/testsuite/g++.dg/template/dtor4.C          |  2 +-

>>   gcc/testsuite/g++.dg/template/error34.C        | 10 +++++-----

>>   .../g++.old-deja/g++.other/inline15.C          |  2 +-

>>   gcc/testsuite/g++.old-deja/g++.pt/ctor2.C      |  2 +-

>>   9 files changed, 42 insertions(+), 13 deletions(-)

>>   create mode 100644 gcc/testsuite/g++.dg/DRs/dr2237.C

>>

>> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c

>> index 591f44f4934..593c45b5888 100644

>> --- a/gcc/cp/parser.c

>> +++ b/gcc/cp/parser.c

>> @@ -6114,6 +6114,15 @@ cp_parser_unqualified_id (cp_parser* parser,

>>   	    return build_min_nt_loc (loc, BIT_NOT_EXPR, make_auto ());

>>   	  }

>>   

>> +	/* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

>> +	   declarator-id of a constructor or destructor.  */

>> +	if (token->type == CPP_TEMPLATE_ID && cxx_dialect >= cxx2a)

>> +	  {

>> +	    if (!cp_parser_simulate_error (parser))

>> +	      error_at (tilde_loc, "template-id not allowed for destructor");

>> +	    return error_mark_node;

>> +	  }

>> +

>>   	/* If there was an explicit qualification (S::~T), first look

>>   	   in the scope given by the qualification (i.e., S).

>>   

>> @@ -28636,7 +28645,9 @@ cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,

>>     if (next_token->type != CPP_NAME

>>         && next_token->type != CPP_SCOPE

>>         && next_token->type != CPP_NESTED_NAME_SPECIFIER

>> -      && next_token->type != CPP_TEMPLATE_ID)

>> +      /* DR 2237 (C++20 only): A simple-template-id is no longer valid as the

>> +	 declarator-id of a constructor or destructor.  */

>> +      && (next_token->type != CPP_TEMPLATE_ID || cxx_dialect >= cxx2a))

>>       return false;

>>   

>>     /* Parse tentatively; we are going to roll back all of the tokens

>> diff --git a/gcc/testsuite/g++.dg/DRs/dr2237.C b/gcc/testsuite/g++.dg/DRs/dr2237.C

>> new file mode 100644

>> index 00000000000..17abdf179c1

>> --- /dev/null

>> +++ b/gcc/testsuite/g++.dg/DRs/dr2237.C

>> @@ -0,0 +1,18 @@

>> +// DR 2237 - Can a template-id name a constructor?

>> +

>> +template<class T>

>> +struct X {

>> +  X<T>(); // { dg-error "expected" "" { target c++2a } }

>> +  X(int); // OK, injected-class-name used

>> +  ~X<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }

>> +};

>> +

>> +// ill-formed since DR1435

>> +template<typename T> X<T>::X<T>() {} // { dg-error "names the constructor|as no template constructors" }

>> +template<typename T> X<T>::~X<T>() {} // { dg-error "template-id not allowed for destructor" "" { target c++2a } }

>> +

>> +struct Q {

>> +  // ill-formed since DR1435

>> +  template<typename T> friend X<T>::X<T>(); // { dg-error "names the constructor|as no template constructors" }

>> +  template<typename T> friend X<T>::~X<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }

>> +};

>> diff --git a/gcc/testsuite/g++.dg/parse/constructor2.C b/gcc/testsuite/g++.dg/parse/constructor2.C

>> index e514e9397e9..87007e9c715 100644

>> --- a/gcc/testsuite/g++.dg/parse/constructor2.C

>> +++ b/gcc/testsuite/g++.dg/parse/constructor2.C

>> @@ -5,7 +5,7 @@ class T

>>   {

>>   public:

>>     T(short,short f=0) {}

>> -  T<TClass>(int f) {}

>> -  T<TClass>(int f=0,const char* b=0) {}

>> +  T<TClass>(int f) {} // { dg-error "expected" "" { target c++2a } }

>> +  T<TClass>(int f=0,const char* b=0) {} // { dg-error "expected" "" { target c++2a } }

>>   };

>>   

>> diff --git a/gcc/testsuite/g++.dg/parse/dtor12.C b/gcc/testsuite/g++.dg/parse/dtor12.C

>> index 1acdfa36b69..d758d3e861d 100644

>> --- a/gcc/testsuite/g++.dg/parse/dtor12.C

>> +++ b/gcc/testsuite/g++.dg/parse/dtor12.C

>> @@ -2,5 +2,5 @@

>>   

>>   template <class T> class a

>>   {

>> -  ~a<T>();

>> +  ~a<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }

>>   };

>> diff --git a/gcc/testsuite/g++.dg/parse/dtor4.C b/gcc/testsuite/g++.dg/parse/dtor4.C

>> index 729ee2fa130..1059c189eff 100644

>> --- a/gcc/testsuite/g++.dg/parse/dtor4.C

>> +++ b/gcc/testsuite/g++.dg/parse/dtor4.C

>> @@ -7,4 +7,4 @@ template <int N> struct X {

>>   };

>>   

>>   template <int N>

>> -X<N>::~X<N>(){}

>> +X<N>::~X<N>(){} // { dg-error "template-id not allowed for destructor" "" { target c++2a } }

>> diff --git a/gcc/testsuite/g++.dg/template/dtor4.C b/gcc/testsuite/g++.dg/template/dtor4.C

>> index 4f277b248bd..917681fc13e 100644

>> --- a/gcc/testsuite/g++.dg/template/dtor4.C

>> +++ b/gcc/testsuite/g++.dg/template/dtor4.C

>> @@ -5,5 +5,5 @@

>>   

>>   template<int> struct A

>>   {

>> -  ~A<0>(); // { dg-error "parse error|declaration" }

>> +  ~A<0>(); // { dg-error "parse error|declaration|template-id" }

>>   };

>> diff --git a/gcc/testsuite/g++.dg/template/error34.C b/gcc/testsuite/g++.dg/template/error34.C

>> index d0cbcaef28e..ab688d9ba8c 100644

>> --- a/gcc/testsuite/g++.dg/template/error34.C

>> +++ b/gcc/testsuite/g++.dg/template/error34.C

>> @@ -3,27 +3,27 @@

>>   

>>   template<typename T> struct A

>>   {

>> -  A<__builtin_offsetof(T, x)>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\)" }

>> +  A<__builtin_offsetof(T, x)>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\)|expected" }

>>   };

>>   

>>   template<typename T> struct B

>>   {

>> -  B<__builtin_offsetof(T, x.y)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\)" }

>> +  B<__builtin_offsetof(T, x.y)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\)|expected" }

>>   };

>>   

>>   template<typename T> struct C

>>   {

>> -  C<__builtin_offsetof(T, x[6])>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\\[6\\\]\\)" }

>> +  C<__builtin_offsetof(T, x[6])>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\\[6\\\]\\)|expected" }

>>   };

>>   

>>   template<typename T> struct D

>>   {

>> -  D<__builtin_offsetof(T, x.y[6].z)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\\[6\\\].z\\)" }

>> +  D<__builtin_offsetof(T, x.y[6].z)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\\[6\\\].z\\)|expected" }

>>   };

>>   

>>   struct E { int x; };

>>   

>>   template<typename T> struct F

>>   {

>> -  F<__builtin_offsetof(E, x)>();	// { dg-error "type/value mismatch|offsetof\\(E, x\\)" }

>> +  F<__builtin_offsetof(E, x)>();	// { dg-error "type/value mismatch|offsetof\\(E, x\\)|expected" }

>>   };

>> diff --git a/gcc/testsuite/g++.old-deja/g++.other/inline15.C b/gcc/testsuite/g++.old-deja/g++.other/inline15.C

>> index 43f7f5e3025..a31c60960a5 100644

>> --- a/gcc/testsuite/g++.old-deja/g++.other/inline15.C

>> +++ b/gcc/testsuite/g++.old-deja/g++.other/inline15.C

>> @@ -1,4 +1,4 @@

>> -// { dg-do assemble  }

>> +// { dg-do assemble { target c++17_down } }

>>   // { dg-options "-O1" }

>>   // Origin: Jakub Jelinek <jakub@redhat.com>

>>   

>> diff --git a/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C b/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C

>> index a8be91ddbb9..4159c84ff56 100644

>> --- a/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C

>> +++ b/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C

>> @@ -4,7 +4,7 @@

>>   

>>   template <class T>

>>   struct A {

>> -  A<T>();

>> +  A<T>(); // { dg-error "expected" "" { target c++2a } }

>>   };

>>   

>>   template <class T>

>>

>> base-commit: 2b2d298ff845ab7a07ffbd51da79473736da3324

>> -- 

>> Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA

>>

> 

> Marek

>

Patch

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 7e5921e039f..810edfa87a9 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -6114,6 +6114,16 @@  cp_parser_unqualified_id (cp_parser* parser,
 	    return build_min_nt_loc (loc, BIT_NOT_EXPR, make_auto ());
 	  }
 
+	/* DR 2237 (C++20 only): A simple-template-id is no longer valid as the
+	   declarator-id of a constructor or destructor.  */
+	if (token->type == CPP_TEMPLATE_ID && cxx_dialect >= cxx2a)
+	  {
+	    if (!cp_parser_uncommitted_to_tentative_parse_p (parser))
+	      error_at (tilde_loc, "template-id not allowed for destructor");
+	    cp_parser_simulate_error (parser);
+	    return error_mark_node;
+	  }
+
 	/* If there was an explicit qualification (S::~T), first look
 	   in the scope given by the qualification (i.e., S).
 
@@ -28675,6 +28685,12 @@  cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,
       if (!constructor_name_p (id, nested_name_specifier))
 	constructor_p = false;
     }
+  /* DR 2237 (C++20 only): A simple-template-id is no longer valid as the
+     declarator-id of a constructor or destructor.  */
+  else if (constructor_p
+	   && cxx_dialect >= cxx2a
+	   && cp_lexer_next_token_is (parser->lexer, CPP_TEMPLATE_ID))
+    constructor_p = false;
   /* If we still think that this might be a constructor-declarator,
      look for a class-name.  */
   else if (constructor_p)
diff --git a/gcc/testsuite/g++.dg/DRs/dr2237.C b/gcc/testsuite/g++.dg/DRs/dr2237.C
new file mode 100644
index 00000000000..17abdf179c1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/DRs/dr2237.C
@@ -0,0 +1,18 @@ 
+// DR 2237 - Can a template-id name a constructor?
+
+template<class T>
+struct X {
+  X<T>(); // { dg-error "expected" "" { target c++2a } }
+  X(int); // OK, injected-class-name used
+  ~X<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }
+};
+
+// ill-formed since DR1435
+template<typename T> X<T>::X<T>() {} // { dg-error "names the constructor|as no template constructors" }
+template<typename T> X<T>::~X<T>() {} // { dg-error "template-id not allowed for destructor" "" { target c++2a } }
+
+struct Q {
+  // ill-formed since DR1435
+  template<typename T> friend X<T>::X<T>(); // { dg-error "names the constructor|as no template constructors" }
+  template<typename T> friend X<T>::~X<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }
+};
diff --git a/gcc/testsuite/g++.dg/parse/constructor2.C b/gcc/testsuite/g++.dg/parse/constructor2.C
index e514e9397e9..87007e9c715 100644
--- a/gcc/testsuite/g++.dg/parse/constructor2.C
+++ b/gcc/testsuite/g++.dg/parse/constructor2.C
@@ -5,7 +5,7 @@  class T
 { 
 public: 
   T(short,short f=0) {} 
-  T<TClass>(int f) {} 
-  T<TClass>(int f=0,const char* b=0) {} 
+  T<TClass>(int f) {} // { dg-error "expected" "" { target c++2a } }
+  T<TClass>(int f=0,const char* b=0) {} // { dg-error "expected" "" { target c++2a } }
 }; 
 
diff --git a/gcc/testsuite/g++.dg/parse/dtor12.C b/gcc/testsuite/g++.dg/parse/dtor12.C
index 1acdfa36b69..d758d3e861d 100644
--- a/gcc/testsuite/g++.dg/parse/dtor12.C
+++ b/gcc/testsuite/g++.dg/parse/dtor12.C
@@ -2,5 +2,5 @@ 
 
 template <class T> class a
 {
-  ~a<T>();
+  ~a<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++2a } }
 };
diff --git a/gcc/testsuite/g++.dg/parse/dtor4.C b/gcc/testsuite/g++.dg/parse/dtor4.C
index 729ee2fa130..1059c189eff 100644
--- a/gcc/testsuite/g++.dg/parse/dtor4.C
+++ b/gcc/testsuite/g++.dg/parse/dtor4.C
@@ -7,4 +7,4 @@  template <int N> struct X {
 };
 
 template <int N>
-X<N>::~X<N>(){}
+X<N>::~X<N>(){} // { dg-error "template-id not allowed for destructor" "" { target c++2a } }
diff --git a/gcc/testsuite/g++.dg/template/dtor4.C b/gcc/testsuite/g++.dg/template/dtor4.C
index 4f277b248bd..917681fc13e 100644
--- a/gcc/testsuite/g++.dg/template/dtor4.C
+++ b/gcc/testsuite/g++.dg/template/dtor4.C
@@ -5,5 +5,5 @@ 
 
 template<int> struct A
 {
-  ~A<0>(); // { dg-error "parse error|declaration" }
+  ~A<0>(); // { dg-error "parse error|declaration|template-id" }
 };
diff --git a/gcc/testsuite/g++.dg/template/error34.C b/gcc/testsuite/g++.dg/template/error34.C
index d0cbcaef28e..ab688d9ba8c 100644
--- a/gcc/testsuite/g++.dg/template/error34.C
+++ b/gcc/testsuite/g++.dg/template/error34.C
@@ -3,27 +3,27 @@ 
 
 template<typename T> struct A
 {
-  A<__builtin_offsetof(T, x)>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\)" }
+  A<__builtin_offsetof(T, x)>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\)|expected" }
 };
 
 template<typename T> struct B
 {
-  B<__builtin_offsetof(T, x.y)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\)" }
+  B<__builtin_offsetof(T, x.y)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\)|expected" }
 };
 
 template<typename T> struct C
 {
-  C<__builtin_offsetof(T, x[6])>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\\[6\\\]\\)" }
+  C<__builtin_offsetof(T, x[6])>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\\[6\\\]\\)|expected" }
 };
 
 template<typename T> struct D
 {
-  D<__builtin_offsetof(T, x.y[6].z)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\\[6\\\].z\\)" }
+  D<__builtin_offsetof(T, x.y[6].z)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\\[6\\\].z\\)|expected" }
 };
 
 struct E { int x; };
 
 template<typename T> struct F
 {
-  F<__builtin_offsetof(E, x)>();	// { dg-error "type/value mismatch|offsetof\\(E, x\\)" }
+  F<__builtin_offsetof(E, x)>();	// { dg-error "type/value mismatch|offsetof\\(E, x\\)|expected" }
 };
diff --git a/gcc/testsuite/g++.old-deja/g++.other/inline15.C b/gcc/testsuite/g++.old-deja/g++.other/inline15.C
index 43f7f5e3025..a31c60960a5 100644
--- a/gcc/testsuite/g++.old-deja/g++.other/inline15.C
+++ b/gcc/testsuite/g++.old-deja/g++.other/inline15.C
@@ -1,4 +1,4 @@ 
-// { dg-do assemble  }
+// { dg-do assemble { target c++17_down } }
 // { dg-options "-O1" }
 // Origin: Jakub Jelinek <jakub@redhat.com>
 
diff --git a/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C b/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C
index a8be91ddbb9..4159c84ff56 100644
--- a/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C
+++ b/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C
@@ -4,7 +4,7 @@ 
 
 template <class T>
 struct A {
-  A<T>();
+  A<T>(); // { dg-error "expected" "" { target c++2a } }
 };
 
 template <class T>