PR c++/87480 - decltype of member access in default template arg

The issue here is that declval<T>().d is considered instantiation-dependent
within a template, as the access to 'd' might depend on the particular
specialization.  But when we're deducing template arguments for a call, we
know that the call and the arguments are non-dependent, so we can do the
substitution as though we aren't in a template.  Which strictly speaking we
aren't, since the default argument is considered a separate definition.

	* pt.c (type_unification_real): Accept a dependent result in
	template context.

From-SVN: r269826

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 2157496745e5d33d568bd6b8a7f1c924a974fbb6..09fb3f2935c333a8e19493f405f0e79705b9d41f 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2019-03-20  Jason Merrill  <jason@redhat.com>
+
+       PR c++/87480 - decltype of member access in default template arg
+       * pt.c (type_unification_real): Accept a dependent result in
+       template context.
+
 2019-03-19  Martin Sebor  <msebor@redhat.com>
 
        PR tree-optimization/89688

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 0acc16d1b92294cd5e58d91303b2584f69270d9a..6c15419e9cc8960945f8de9fca2d7b5405e26a6b 100644 (file)
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -21005,8 +21005,15 @@ type_unification_real (tree tparms,
            }
          else
            {
+             /* Even if the call is happening in template context, getting
+                here means it's non-dependent, and a default argument is
+                considered a separate definition under [temp.decls], so we can
+                do this substitution without processing_template_decl.  This
+                is important if the default argument contains something that
+                might be instantiation-dependent like access (87480).  */
+             processing_template_decl_sentinel s;
              tree substed = NULL_TREE;
-             if (saw_undeduced == 1 && processing_template_decl == 0)
+             if (saw_undeduced == 1)
                {
                  /* First instatiate in template context, in case we still
                     depend on undeduced template parameters.  */

diff --git a/gcc/testsuite/g++.dg/cpp0x/fntmpdefarg11.C b/gcc/testsuite/g++.dg/cpp0x/fntmpdefarg11.C
new file mode 100644 (file)
index 0000000..86c8ea9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/fntmpdefarg11.C
@@ -0,0 +1,15 @@
+// PR c++/87480
+// { dg-do compile { target c++11 } }
+
+template<typename T> T&& declval();
+
+template <typename T, typename = decltype(declval<T>().d)> void f(T) { }
+
+struct A {
+  double d;
+};
+
+template <typename>
+void j(A& a) {
+  f(a);
+}