From: Jason Merrill <jason@redhat.com>
Date: Fri, 22 May 2026 16:57:09 +0000 (-0400)
Subject: c++: defaulted ctor vs template ctor [PR125135]
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=fe059756ddc4ec4e357a73d6385fd93db202c66e;p=thirdparty%2Fgcc.git

c++: defaulted ctor vs template ctor [PR125135]

Here we were getting into a CWG1092 cycle again through
check_non_deducible_conversions, trying to lazily declare the RE move
constructor, looking for a constructor to move A, considering the
constructor template which takes RE&, and so trying to lazily declare the RE
constructors again.

Let's break the cycle in the same way.

	PR c++/125135

gcc/cp/ChangeLog:

	* pt.cc (check_non_deducible_conversions): Handle LOOKUP_DEFAULTED.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/implicit18.C: New test.
---

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 91aa9f55602..3910017a9dc 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -23924,6 +23924,16 @@ check_non_deducible_conversions (tree parms, const tree *args, unsigned nargs,
 	  conversion **conv_p = convs ? &convs[ia+offset] : NULL;
 	  int lflags = conv_flags (ia, nargs, fn, arg, flags);
 
+	  /* As in add_function_candidate, don't consider conversion to an
+	     unrelated type when LOOKUP_DEFAULTED.  */
+	  if ((flags & LOOKUP_DEFAULTED)
+	      && ia == 0
+	      && (DECL_CONSTRUCTOR_P (fn)
+		  || DECL_ASSIGNMENT_OPERATOR_P (fn))
+	      && !reference_related_p (non_reference (parm),
+				       DECL_CONTEXT (fn)))
+	    return 1;
+
 	  if (check_non_deducible_conversion (parm, arg, strict, lflags,
 					      conv_p, explain_p, noninst_only_p))
 	    return 1;
diff --git a/gcc/testsuite/g++.dg/cpp0x/implicit18.C b/gcc/testsuite/g++.dg/cpp0x/implicit18.C
new file mode 100644
index 00000000000..5b3730f14ec
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/implicit18.C
@@ -0,0 +1,20 @@
+// PR c++/125135
+// { dg-do compile { target c++11 } }
+
+template <typename T>
+struct A
+{
+  template <typename... Ts> // variadic causea ICE.
+  A(T&, const Ts&...){} // T& arg causes ICE.
+
+  A(const A&) = delete; // causes ICE.
+};
+
+struct RE
+{
+  RE(): a(*this) {}
+
+  A<RE> a;
+};
+
+RE re;