[C++ Patch] PR 68754 ("Explicitly defaulted constexpr assignment operator fails to compile")

[C++ Patch] PR 68754 ("Explicitly defaulted constexpr assignment operator fails to compile")

[Paolo Carlini]

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Hi,

the main issue, a C++14 rejects-valid, is already fixed in trunk, and a 
while ago I added a testcase for that. However, Andrew noticed that in 
C++11 mode we emit redundant and also a bit puzzling diagnostic (ending 
with one of those annoying "... because:" and nothing after which 
unfortunately we emit in some other cases too). Comparing to, eg, clang 
too, I think we can make progress by simply returning early after the 
first hard error. Also, as an additional tweak, we might replace the 
second error with an inform, per the usual scheme. Tested x86_64-linux.

Thanks, Paolo.

//////////////////////////


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/cp
2017-09-29  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/68754
	* method.c (defaulted_late_check): Early return if the defaulted
	declaration does not match the expected signature.

/testsuite
2017-09-29  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/68754
	* g++.dg/cpp1y/constexpr-68754.C: Move...
	* g++.dg/cpp0x/constexpr-68754.C: ... here, adjust.

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Index: cp/method.c
===================================================================
--- cp/method.c	(revision 253283)
+++ cp/method.c	(working copy)
@@ -2191,9 +2191,11 @@ defaulted_late_check (tree fn)
       || !compparms (TYPE_ARG_TYPES (TREE_TYPE (fn)),
 		     TYPE_ARG_TYPES (TREE_TYPE (implicit_fn))))
     {
-      error ("defaulted declaration %q+D", fn);
-      error_at (DECL_SOURCE_LOCATION (fn),
-		"does not match expected signature %qD", implicit_fn);
+      error ("defaulted declaration %q+D does not match the "
+	     "expected signature", fn);
+      inform (DECL_SOURCE_LOCATION (fn),
+	      "expected signature: %qD", implicit_fn);
+      return;
     }
 
   if (DECL_DELETED_FN (implicit_fn))
Index: testsuite/g++.dg/cpp0x/constexpr-68754.C
===================================================================
--- testsuite/g++.dg/cpp0x/constexpr-68754.C	(revision 253283)
+++ testsuite/g++.dg/cpp0x/constexpr-68754.C	(working copy)
@@ -1,7 +1,7 @@
 // PR c++/68754
-// { dg-do compile { target c++14 } }
+// { dg-do compile { target c++11 } }
 
 struct base { };
 struct derived : base {
-  constexpr derived& operator=(derived const&) = default;
+  constexpr derived& operator=(derived const&) = default; // { dg-error "defaulted declaration" "" { target { ! c++14 } } }
 };
Index: testsuite/g++.dg/cpp1y/constexpr-68754.C
===================================================================
--- testsuite/g++.dg/cpp1y/constexpr-68754.C	(revision 253283)
+++ testsuite/g++.dg/cpp1y/constexpr-68754.C	(working copy)
@@ -1,7 +0,0 @@
-// PR c++/68754
-// { dg-do compile { target c++14 } }
-
-struct base { };
-struct derived : base {
-  constexpr derived& operator=(derived const&) = default;
-};

Re: [C++ Patch] PR 68754 ("Explicitly defaulted constexpr assignment operator fails to compile")

[Nathan Sidwell]

On 09/29/2017 10:04 AM, Paolo Carlini wrote:
> Hi,
> 
> the main issue, a C++14 rejects-valid, is already fixed in trunk, and a 
> while ago I added a testcase for that. However, Andrew noticed that in 
> C++11 mode we emit redundant and also a bit puzzling diagnostic (ending 
> with one of those annoying "... because:" and nothing after which 
> unfortunately we emit in some other cases too). Comparing to, eg, clang 
> too, I think we can make progress by simply returning early after the 
> first hard error. Also, as an additional tweak, we might replace the 
> second error with an inform, per the usual scheme. Tested x86_64-linux.

Looks good, thanks.

nathan

-- 
Nathan Sidwell