diff mbox series

[v3] c++: DR2237, cdtor and template-id tweaks [PR107126]

Message ID ZcVHHLIBYTp0eB5g@redhat.com
State New
Headers show
Series [v3] c++: DR2237, cdtor and template-id tweaks [PR107126] | expand

Commit Message

Marek Polacek Feb. 8, 2024, 9:26 p.m. UTC 
On Wed, Feb 07, 2024 at 05:19:56PM -0500, Jason Merrill wrote:
> On 2/5/24 22:11, Marek Polacek wrote:
> > On Mon, Feb 05, 2024 at 10:14:34AM -0500, Jason Merrill wrote:
> > > On 2/3/24 10:24, Marek Polacek wrote:
> > > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > > > 
> > > > I'm not certain OPT_Wc__20_extensions is the best thing for something
> > > > from [diff.cpp17]; would you prefer something else?
> > > 
> > > I think it wants its own flag, that is enabled in C++20 or by
> > > -Wc++20-compat.
> > 
> > That seems best.  I called it -Wdeprecated-template-id-cdtor.
> > > > +	    if (cxx_dialect >= cxx20)
> > > > +	      {
> > > > +		if (!cp_parser_simulate_error (parser))
> > > > +		  pedwarn (tilde_loc, OPT_Wc__20_extensions,
> > > > +			   "template-id not allowed for destructor");
> > > > +		return error_mark_node;
> > > > +	      }
> > > > +	    warning_at (tilde_loc, OPT_Wc__20_compat,
> > > > +			"template-id not allowed for destructor in C++20");
> > > 
> > > After a pedwarn we should accept the code, not return error_mark_node.
> > 
> > /facepalm, yes.
> > > I'm also concerned about pedwarn/warnings not guarded by
> > > !cp_parser_uncommited_to_tentative_parse; that often leads to warning about
> > > a tentative parse as a declaration that is eventually abandoned in favor of
> > > a perfectly fine parse as an expression.
> > 
> > Done.
> > > It would be good for cp_parser_context to add a vec of warnings to emit at
> > > cp_parser_parse_definitely time, and then
> > > cp_parser_pedwarn/cp_parser_warning to fill it...
> > 
> > That would be nice; I don't think we can fix bugs like PR61259 otherwise.
> > 
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > 
> > -- >8 --
> > Since my r11-532 changes to implement DR2237, for this test:
> > 
> >    template<typename T>
> >    struct S {
> >      S<T>();
> >    };
> > 
> > in C++20 we emit the ugly:
> > 
> > q.C:3:8: error: expected unqualified-id before ')' token
> >      3 |   S<T>();
> > 
> > which doesn't explain what the problem is.  This patch improves that
> > diagnostic, reduces the error to a pedwarn, and adds a -Wc++20-compat
> > diagnostic.  We now say:
> > 
> > q.C:3:7: warning: template-id not allowed for constructor in C++20 [-Wdeprecated-template-id-cdtor]
> >      3 |   S<T>();
> > q.C:3:7: note: remove the '< >'
> > 
> > This patch does *not* fix
> > <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202#c8>
> > where the C++20 diagnostic is missing altogether.
> > 
> > -Wc++20-compat triggered in libitm/; I sent a patch for that.
> > 
> > 	DR 2237
> > 	PR c++/107126
> > 	PR c++/97202
> > 
> > gcc/c-family/ChangeLog:
> > 
> > 	* c-opts.cc (c_common_post_options): In C++20 or with -Wc++20-compat,
> > 	turn on -Wdeprecated-template-id-cdtor.
> > 	* c.opt (Wdeprecated-template-id-cdtor): New.
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* parser.cc (cp_parser_unqualified_id): Downgrade the DR2237 error to
> > 	a pedwarn.
> > 	(cp_parser_constructor_declarator_p): Likewise.
> > 
> > diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> > index 3748ccd49ff..473eaf4f1f7 100644
> > --- a/gcc/cp/parser.cc
> > +++ b/gcc/cp/parser.cc
> > @@ -6717,12 +6717,17 @@ cp_parser_unqualified_id (cp_parser* parser,
> >   	/* 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 && declarator_p
> > -	    && cxx_dialect >= cxx20)
> > +	if (token->type == CPP_TEMPLATE_ID
> > +	    && declarator_p
> > +	    && !cp_parser_uncommitted_to_tentative_parse_p (parser)
> > +	    && !cp_parser_simulate_error (parser))
> 
> Calling both _uncommitted_ and _simulate_ here is redundant since _simulate_
> checks _uncommitted_; since you check _uncommitted_ first, _simulate_ will
> never do anything.

Oops, pardon me.
 
> And checking either of them before cxx_dialect seems wrong; we don't want
> _simulate_ in pre-C++20 mode where it isn't an error, but we do want
> _simulate_ in C++20 mode when uncommitted.

I see.

> > @@ -32550,6 +32555,19 @@ cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,
> >     /* We did not really want to consume any tokens.  */
> >     cp_parser_abort_tentative_parse (parser);
> > +  /* DR 2237 (C++20 only): A simple-template-id is no longer valid as the
> > +     declarator-id of a constructor or destructor.  */
> > +  if (constructor_p
> > +      && saw_template_id
> > +      && !cp_parser_uncommitted_to_tentative_parse_p (parser))
> 
> As above, checking _uncommitted_ before cxx_dialect seems wrong for C++20.
> 
> If testing succeeded with this patch, maybe we can't get here while parsing
> tentatively, and we just want a checking_assert (!_uncommitted_) in both
> places?  Or would that break on 97202?

I can add the assert to the second spot, but adding it to the first one
causes crashes.  So maybe like this, then?

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

-- >8 --
Since my r11-532 changes to implement DR2237, for this test:

  template<typename T>
  struct S {
    S<T>();
  };

in C++20 we emit the ugly:

q.C:3:8: error: expected unqualified-id before ')' token
    3 |   S<T>();

which doesn't explain what the problem is.  This patch improves that
diagnostic, reduces the error to a pedwarn, and adds a -Wc++20-compat
diagnostic.  We now say:

q.C:3:7: warning: template-id not allowed for constructor in C++20 [-Wdeprecated-template-id-cdtor]
    3 |   S<T>();
q.C:3:7: note: remove the '< >'

This patch does *not* fix
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202#c8>
where the C++20 diagnostic is missing altogether.

-Wc++20-compat triggered in libitm/; I sent a patch for that.

	DR 2237
	PR c++/107126
	PR c++/97202

gcc/c-family/ChangeLog:

	* c-opts.cc (c_common_post_options): In C++20 or with -Wc++20-compat,
	turn on -Wdeprecated-template-id-cdtor.
	* c.opt (Wdeprecated-template-id-cdtor): New.

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_unqualified_id): Downgrade the DR2237 error to
	a pedwarn.
	(cp_parser_constructor_declarator_p): Likewise.

gcc/ChangeLog:

	* doc/invoke.texi: Document -Wdeprecated-template-id-cdtor.

gcc/testsuite/ChangeLog:

	* g++.dg/DRs/dr2237.C: Adjust dg-error.
	* g++.dg/parse/constructor2.C: Likewise.
	* g++.dg/template/error34.C: Likewise.
	* g++.old-deja/g++.pt/ctor2.C: Likewise.
	* g++.dg/DRs/dr2237-2.C: New test.
	* g++.dg/DRs/dr2237-3.C: New test.
	* g++.dg/DRs/dr2237-4.C: New test.
	* g++.dg/warn/Wdeprecated-template-id-cdtor-1.C: New test.
	* g++.dg/warn/Wdeprecated-template-id-cdtor-2.C: New test.
	* g++.dg/warn/Wdeprecated-template-id-cdtor-3.C: New test.
	* g++.dg/warn/Wdeprecated-template-id-cdtor-4.C: New test.
---
 gcc/c-family/c-opts.cc                        |  5 +++
 gcc/c-family/c.opt                            |  4 +++
 gcc/cp/parser.cc                              | 36 ++++++++++++++-----
 gcc/doc/invoke.texi                           | 18 ++++++++++
 gcc/testsuite/g++.dg/DRs/dr2237-2.C           |  9 +++++
 gcc/testsuite/g++.dg/DRs/dr2237-3.C           | 16 +++++++++
 gcc/testsuite/g++.dg/DRs/dr2237-4.C           | 11 ++++++
 gcc/testsuite/g++.dg/DRs/dr2237.C             |  2 +-
 gcc/testsuite/g++.dg/parse/constructor2.C     | 16 ++++-----
 gcc/testsuite/g++.dg/template/error34.C       | 10 +++---
 .../warn/Wdeprecated-template-id-cdtor-1.C    |  9 +++++
 .../warn/Wdeprecated-template-id-cdtor-2.C    |  9 +++++
 .../warn/Wdeprecated-template-id-cdtor-3.C    |  9 +++++
 .../warn/Wdeprecated-template-id-cdtor-4.C    |  9 +++++
 gcc/testsuite/g++.old-deja/g++.pt/ctor2.C     |  2 +-
 15 files changed, 142 insertions(+), 23 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/DRs/dr2237-2.C
 create mode 100644 gcc/testsuite/g++.dg/DRs/dr2237-3.C
 create mode 100644 gcc/testsuite/g++.dg/DRs/dr2237-4.C
 create mode 100644 gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-1.C
 create mode 100644 gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-2.C
 create mode 100644 gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-3.C
 create mode 100644 gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-4.C


base-commit: 232ffb61ceb63c4a86a8bc67f1db989c2124db5f

Comments

Jason Merrill Feb. 9, 2024, 3:20 p.m. UTC | #1 
On 2/8/24 16:26, Marek Polacek wrote:
> This patch does *not* fix
> <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202#c8>
> where the C++20 diagnostic is missing altogether.

What would it take to fix that as well?

> 	* doc/invoke.texi: Document -Wdeprecated-template-id-cdtor.

Was it ever deprecated?  I'm not seeing that in

https://timsong-cpp.github.io/cppwp/n4659/#depr (C++17)

Let's drop the word "deprecated" from the option name and documentation.

> @@ -32331,11 +32338,11 @@ 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
> -      /* 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 >= cxx20))
> +      && next_token->type != CPP_TEMPLATE_ID)
>       return false;
>   
> +  const bool saw_template_id = (next_token->type == CPP_TEMPLATE_ID);

Please incorporate your "further DR2237 fix" patch into this one.

> @@ -32552,6 +32559,19 @@ cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,
>     /* We did not really want to consume any tokens.  */
>     cp_parser_abort_tentative_parse (parser);
>   
> +  /* DR 2237 (C++20 only): A simple-template-id is no longer valid as the
> +     declarator-id of a constructor or destructor.  */
> +  if (constructor_p && saw_template_id)
> +    {
> +      gcc_checking_assert
> +	(!cp_parser_uncommitted_to_tentative_parse_p (parser));

Now I see the abort_ just above, so this seems unnecessary after all.

Thanks,
Jason
diff mbox series

Patch

diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
index b845aff2226..d2358e2009a 100644
--- a/gcc/c-family/c-opts.cc
+++ b/gcc/c-family/c-opts.cc
@@ -998,6 +998,11 @@  c_common_post_options (const char **pfilename)
 		       warn_deprecated_enum_float_conv,
 		       cxx_dialect >= cxx20 && warn_deprecated);
 
+  /* -Wdeprecated-template-id-cdtor is enabled by default in C++20.  */
+  SET_OPTION_IF_UNSET (&global_options, &global_options_set,
+		       warn_deprecated_template_id_cdtor,
+		       cxx_dialect >= cxx20 || warn_cxx20_compat);
+
   /* Declone C++ 'structors if -Os.  */
   if (flag_declone_ctor_dtor == -1)
     flag_declone_ctor_dtor = optimize_size;
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 9c0a28092fc..2e1d07b66de 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -642,6 +642,10 @@  C++ ObjC++ Var(warn_deprecated_enum_float_conv) Warning
 Warn about deprecated arithmetic conversions on operands where one is of enumeration
 type and the other is of a floating-point type.
 
+Wdeprecated-template-id-cdtor
+C++ ObjC++ Var(warn_deprecated_template_id_cdtor) Warning
+Warn about deprecated simple-template-id in a constructor or destructor.
+
 Wdesignated-init
 C ObjC Var(warn_designated_init) Init(1) Warning
 Warn about positional initialization of structs requiring designated initializers.
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index c4292c49ce2..759ba7e54c4 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -6719,12 +6719,19 @@  cp_parser_unqualified_id (cp_parser* parser,
 
 	/* 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 && declarator_p
-	    && cxx_dialect >= cxx20)
+	if (token->type == CPP_TEMPLATE_ID && declarator_p)
 	  {
-	    if (!cp_parser_simulate_error (parser))
-	      error_at (tilde_loc, "template-id not allowed for destructor");
-	    return error_mark_node;
+	    auto_diagnostic_group d;
+	    bool w = false;
+	    if (cxx_dialect >= cxx20 && !cp_parser_simulate_error (parser))
+	      w = pedwarn (tilde_loc, OPT_Wdeprecated_template_id_cdtor,
+			   "template-id not allowed for destructor in C++20");
+	    else if (cxx_dialect < cxx20
+		     && !cp_parser_uncommitted_to_tentative_parse_p (parser))
+	      w = warning_at (tilde_loc, OPT_Wdeprecated_template_id_cdtor,
+			      "template-id not allowed for destructor in C++20");
+	    if (w)
+	      inform (tilde_loc, "remove the %qs", "< >");
 	  }
 
 	/* If there was an explicit qualification (S::~T), first look
@@ -32331,11 +32338,11 @@  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
-      /* 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 >= cxx20))
+      && next_token->type != CPP_TEMPLATE_ID)
     return false;
 
+  const bool saw_template_id = (next_token->type == CPP_TEMPLATE_ID);
+
   /* Parse tentatively; we are going to roll back all of the tokens
      consumed here.  */
   cp_parser_parse_tentatively (parser);
@@ -32552,6 +32559,19 @@  cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,
   /* We did not really want to consume any tokens.  */
   cp_parser_abort_tentative_parse (parser);
 
+  /* DR 2237 (C++20 only): A simple-template-id is no longer valid as the
+     declarator-id of a constructor or destructor.  */
+  if (constructor_p && saw_template_id)
+    {
+      gcc_checking_assert
+	(!cp_parser_uncommitted_to_tentative_parse_p (parser));
+      auto_diagnostic_group d;
+      if (emit_diagnostic (cxx_dialect >= cxx20 ? DK_PEDWARN : DK_WARNING,
+			   input_location, OPT_Wdeprecated_template_id_cdtor,
+			   "template-id not allowed for constructor in C++20"))
+	inform (input_location, "remove the %qs", "< >");
+    }
+
   return constructor_p;
 }
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 71339b8b30f..5bd65bd02be 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -255,6 +255,7 @@  in the following sections.
 -Wdelete-non-virtual-dtor  -Wno-deprecated-array-compare
 -Wdeprecated-copy -Wdeprecated-copy-dtor
 -Wno-deprecated-enum-enum-conversion -Wno-deprecated-enum-float-conversion
+-Wno-deprecated-template-id-cdtor
 -Weffc++ -Wno-elaborated-enum-base
 -Wno-exceptions -Wextra-semi  -Wno-inaccessible-base
 -Wno-inherited-variadic-ctor  -Wno-init-list-lifetime
@@ -3989,6 +3990,23 @@  bool b = e <= 3.7;
 @option{-std=c++20}.  In pre-C++20 dialects, this warning can be enabled
 by @option{-Wenum-conversion}.
 
+@opindex Wdeprecated-template-id-cdtor
+@opindex Wno-deprecated-template-id-cdtor
+@item -Wno-deprecated-template-id-cdtor @r{(C++ and Objective-C++ only)}
+Disable the warning about the deprecated use of simple-template-id as the
+declarator-id of a constructor or destructor, which became invalid in C++20
+via DR 2237.  For example:
+
+@smallexample
+template<typename T> struct S @{
+  S<T>(); // should be S();
+  ~S<T>();  // should be ~S();
+@};
+@end smallexample
+
+@option{-Wdeprecated-template-id-cdtor} is enabled by default with
+@option{-std=c++20}; it is also enabled by @option{-Wc++20-compat}.
+
 @opindex Welaborated-enum-base
 @opindex Wno-elaborated-enum-base
 @item -Wno-elaborated-enum-base
diff --git a/gcc/testsuite/g++.dg/DRs/dr2237-2.C b/gcc/testsuite/g++.dg/DRs/dr2237-2.C
new file mode 100644
index 00000000000..1d99347229c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/DRs/dr2237-2.C
@@ -0,0 +1,9 @@ 
+// DR 2237 - Can a template-id name a constructor?
+// { dg-options "" }
+
+template<class T>
+struct X {
+  X<T>(); // { dg-warning "template-id not allowed for constructor" "" { target c++20 } }
+  X(int); // OK, injected-class-name used
+  ~X<T>(); // { dg-warning "template-id not allowed for destructor" "" { target c++20 } }
+};
diff --git a/gcc/testsuite/g++.dg/DRs/dr2237-3.C b/gcc/testsuite/g++.dg/DRs/dr2237-3.C
new file mode 100644
index 00000000000..c8ad6852389
--- /dev/null
+++ b/gcc/testsuite/g++.dg/DRs/dr2237-3.C
@@ -0,0 +1,16 @@ 
+// PR c++/107126
+// { dg-options "" }
+
+template<typename T>
+struct C
+{
+    ~C();
+};
+template<typename T>
+C<T>::~C<T>()	      // { dg-warning "template-id not allowed for destructor" "" { target c++20 } }
+{
+}
+int main()
+{
+    C<int> c;;
+}
diff --git a/gcc/testsuite/g++.dg/DRs/dr2237-4.C b/gcc/testsuite/g++.dg/DRs/dr2237-4.C
new file mode 100644
index 00000000000..a358dd521b5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/DRs/dr2237-4.C
@@ -0,0 +1,11 @@ 
+// PR c++/97202
+// { dg-options "" }
+
+template<typename T>
+struct F
+{
+  F<T>();  // { dg-warning "template-id not allowed for constructor" "" { target c++20 } }
+};
+
+template<typename T>
+inline F<T>::F() { }
diff --git a/gcc/testsuite/g++.dg/DRs/dr2237.C b/gcc/testsuite/g++.dg/DRs/dr2237.C
index f3d6d11e61e..830c8f5a2a6 100644
--- a/gcc/testsuite/g++.dg/DRs/dr2237.C
+++ b/gcc/testsuite/g++.dg/DRs/dr2237.C
@@ -2,7 +2,7 @@ 
 
 template<class T>
 struct X {
-  X<T>(); // { dg-error "expected" "" { target c++20 } }
+  X<T>(); // { dg-error "template-id not allowed for constructor" "" { target c++20 } }
   X(int); // OK, injected-class-name used
   ~X<T>(); // { dg-error "template-id not allowed for destructor" "" { target c++20 } }
 };
diff --git a/gcc/testsuite/g++.dg/parse/constructor2.C b/gcc/testsuite/g++.dg/parse/constructor2.C
index d620f41e027..e4b2ad3f2fe 100644
--- a/gcc/testsuite/g++.dg/parse/constructor2.C
+++ b/gcc/testsuite/g++.dg/parse/constructor2.C
@@ -1,11 +1,11 @@ 
 // PR c++/14260
 
-template <class TClass> 
-class T 
-{ 
-public: 
-  T(short,short f=0) {} 
-  T<TClass>(int f) {} // { dg-error "expected" "" { target c++20 } }
-  T<TClass>(int f=0,const char* b=0) {} // { dg-error "expected" "" { target c++20 } }
-}; 
+template <class TClass>
+class T
+{
+public:
+  T(short,short f=0) {}
+  T<TClass>(int f) {} // { dg-error "template-id not allowed for constructor" "" { target c++20 } }
+  T<TClass>(int f=0,const char* b=0) {} // { dg-error "template-id not allowed for constructor" "" { target c++20 } }
+};
 
diff --git a/gcc/testsuite/g++.dg/template/error34.C b/gcc/testsuite/g++.dg/template/error34.C
index ab688d9ba8c..921cb8fb729 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\\)|expected" }
+  A<__builtin_offsetof(T, x)>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\)|template-id" }
 };
 
 template<typename T> struct B
 {
-  B<__builtin_offsetof(T, x.y)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\)|expected" }
+  B<__builtin_offsetof(T, x.y)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\)|template-id" }
 };
 
 template<typename T> struct C
 {
-  C<__builtin_offsetof(T, x[6])>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\\[6\\\]\\)|expected" }
+  C<__builtin_offsetof(T, x[6])>();	// { dg-error "type/value mismatch|offsetof\\(T, x\\\[6\\\]\\)|template-id" }
 };
 
 template<typename T> struct D
 {
-  D<__builtin_offsetof(T, x.y[6].z)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\\[6\\\].z\\)|expected" }
+  D<__builtin_offsetof(T, x.y[6].z)>();	// { dg-error "type/value mismatch|offsetof\\(T, x.y\\\[6\\\].z\\)|template-id" }
 };
 
 struct E { int x; };
 
 template<typename T> struct F
 {
-  F<__builtin_offsetof(E, x)>();	// { dg-error "type/value mismatch|offsetof\\(E, x\\)|expected" }
+  F<__builtin_offsetof(E, x)>();	// { dg-error "type/value mismatch|offsetof\\(E, x\\)|template-id" }
 };
diff --git a/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-1.C b/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-1.C
new file mode 100644
index 00000000000..429490708bc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-1.C
@@ -0,0 +1,9 @@ 
+// PR c++/107126
+// { dg-do compile }
+// { dg-options "-Wc++20-compat" }
+
+template<class T>
+struct X {
+  X<T>(); // { dg-warning "template-id not allowed for constructor" }
+  ~X<T>(); // { dg-warning "template-id not allowed for destructor" }
+};
diff --git a/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-2.C b/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-2.C
new file mode 100644
index 00000000000..d76b647c615
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-2.C
@@ -0,0 +1,9 @@ 
+// PR c++/107126
+// { dg-do compile }
+// { dg-options "-Wdeprecated-template-id-cdtor" }
+
+template<class T>
+struct X {
+  X<T>(); // { dg-warning "template-id not allowed for constructor" }
+  ~X<T>(); // { dg-warning "template-id not allowed for destructor" }
+};
diff --git a/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-3.C b/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-3.C
new file mode 100644
index 00000000000..80fc2ff7739
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-3.C
@@ -0,0 +1,9 @@ 
+// PR c++/107126
+// { dg-do compile }
+// { dg-options "-Wc++20-compat -Wno-deprecated-template-id-cdtor" }
+
+template<class T>
+struct X {
+  X<T>(); // { dg-bogus "template-id not allowed for constructor" }
+  ~X<T>(); // { dg-bogus "template-id not allowed for destructor" }
+};
diff --git a/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-4.C b/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-4.C
new file mode 100644
index 00000000000..6f1747701da
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wdeprecated-template-id-cdtor-4.C
@@ -0,0 +1,9 @@ 
+// PR c++/107126
+// { dg-do compile }
+// { dg-options "-Wdeprecated-template-id-cdtor -Wno-c++20-compat" }
+
+template<class T>
+struct X {
+  X<T>(); // { dg-warning "template-id not allowed for constructor" }
+  ~X<T>(); // { dg-warning "template-id not allowed for destructor" }
+};
diff --git a/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C b/gcc/testsuite/g++.old-deja/g++.pt/ctor2.C
index bf418ba48c7..56b4232d04b 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>(); // { dg-error "expected" "" { target c++20 } }
+  A<T>(); // { dg-error "template-id" "" { target c++20 } }
 };
 
 template <class T>