This issue is similar to PR 87480; in both cases we were doing non-dependent
substitution with processing_template_decl set, leading to member access
expressions seeming still instantiation-dependent, and therefore decltype
not being simplified to its actual type. And as in that PR, the fix is to
clear processing_template_decl while substituting a default template
argument.
Tested x86_64-pc-linux-gnu, applying to trunk.
* pt.c (most_specialized_partial_spec): Clear
processing_template_decl.
---
gcc/cp/pt.c | 5 ++
gcc/testsuite/g++.dg/cpp0x/sfinae64.C | 69 +++++++++++++++++++++++++++
gcc/cp/ChangeLog | 6 +++
3 files changed, 80 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/sfinae64.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index afb7ece57d1..05d5371d8a6 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -23550,6 +23550,11 @@ most_specialized_partial_spec (tree target,
tsubst_flags_t complain)
args = INNERMOST_TEMPLATE_ARGS (args);
}
+ /* The caller hasn't called push_to_top_level yet, but we need
+ get_partial_spec_bindings to be done in non-template context so that we'll
+ fully resolve everything. */
+ processing_template_decl_sentinel ptds;
+
for (t = DECL_TEMPLATE_SPECIALIZATIONS (main_tmpl); t; t = TREE_CHAIN (t))
{
tree spec_args;
diff --git a/gcc/testsuite/g++.dg/cpp0x/sfinae64.C
b/gcc/testsuite/g++.dg/cpp0x/sfinae64.C
new file mode 100644
index 00000000000..f35b81268a2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/sfinae64.C
@@ -0,0 +1,69 @@
+// PR c++/87748
+// { dg-do compile { target c++11 } }
+
+template <class T> T&& declval();
+template <bool B, class T> struct enable_if;
+template <class T> struct enable_if <true, T> { typedef T type; };
+struct true_type { static const bool value = true; };
+struct false_type { static const bool value = false; };
+
+struct string
+{
+ string (const char *p);
+};
+
+/// Template to map all type arguments to void, useful for SFINAE, see also
WG21 N3911.
+template<class...> using void_t = void;
+
+/// REQUIRES<value> - Simplified version of enable_if<> to use SFINAE in
function templates.
+template<bool value> using REQUIRES = typename ::enable_if<value, bool>::type;
+
+/// DerivesString<T> - Check if @a T is of type 'string'.
+template<class T> struct DerivesString
+{
+ static const int value = __is_same_as (T, string);
+};
+
+/// Has__aida_visit__<T,Visitor> - Check if @a T provides a member template
__aida_visit__<>(Visitor).
+template<class, class, class = void> struct Has__aida_visit__ : false_type {};
+template<class T, class V>
+struct Has__aida_visit__<T, V, void_t< decltype (declval<T>().template
__aida_visit__<V> (*(V*) 0)) >> : true_type {};
+
+struct Foo {
+ template<class V> void __accept__ (V*);
+};
+
+/// Base template for Visitor classes, dispatches operator() to visit_<type>()
methods.
+template<class DerivedVisitor>
+class VisitorDispatcher {
+ DerivedVisitor* derived () { return static_cast<DerivedVisitor*> (this); }
+protected:
+ typedef const char* Name; ///< Member name argument type for visit() methods.
+public:
+
+ // dispatch for calls like: visitor (field, "field");
+
+ template<class A,
+ REQUIRES< (!Has__aida_visit__<A, DerivedVisitor>::value) > = true>
+ void operator() (A &a, Name n)
+ { return derived()->visit_string (a, n); }
+};
+
+class PspecVisitor : public VisitorDispatcher<PspecVisitor> {
+public:
+ void visit_string (::string &a, Name name);
+};
+
+int
+main (int argc, char *argv[])
+{
+#ifdef WITHASSERT // define this to fix g++-8.1.1
+ static_assert (Has__aida_visit__<string, PspecVisitor>::value == false, "");
+#endif
+ PspecVisitor v;
+ string str ("A string");
+ v (str, "some_string");
+ static_assert (Has__aida_visit__<string, PspecVisitor>::value == false, "");
+ return 0;
+}
+// g++ -std=gnu++14 -Wall -O2 aidavisit.cc && ./a.out
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 16f1b8e1aae..66171b2ccdf 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2019-03-25 Jason Merrill <ja...@redhat.com>
+
+ PR c++/87748 - substitution failure error with decltype.
+ * pt.c (most_specialized_partial_spec): Clear
+ processing_template_decl.
+
2019-03-22 Jakub Jelinek <ja...@redhat.com>
PR c++/60702
base-commit: 1954998fae2cf349308b55faca0c7b0ecf1b2462
--
2.20.1
