c++: Lambda in friend of constrained class [PR94645]

In the testcase below, when grokfndecl processes the operator() decl for the
lambda inside the friend function foo, processing_template_decl is rightly 1,
but template_class_depth on the lambda's closure type incorrectly returns 0
instead of 1.

Since processing_template_decl > template_class_depth, this makes grokfndecl
think that the operator() has its own set of template arguments, and so we
attach the innermost set of constraints -- those belonging to struct l -- to the
operator() decl.  We then get confused when checking constraints_satisfied_p on
the operator() because it doesn't have template information and yet has
constraints associated with it.

This patch fixes template_class_depth to return the correct template nesting
level in cases like these, in that when it hits a friend function it walks into
the DECL_FRIEND_CONTEXT of the friend rather than into the CP_DECL_CONTEXT.

gcc/cp/ChangeLog:

	PR c++/94645
	* pt.c (template_class_depth): Walk into the DECL_FRIEND_CONTEXT of a
	friend declaration rather than into its CP_DECL_CONTEXT.

gcc/testsuite/ChangeLog:

	PR c++/94645
	* g++.dg/cpp2a/concepts-lambda6.C: New test.

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index fa150e3..6506f28 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2020-04-23  Patrick Palka  <ppalka@redhat.com>
+
+       PR c++/94645
+       * pt.c (template_class_depth): Walk into the DECL_FRIEND_CONTEXT of a
+       friend declaration rather than into its CP_DECL_CONTEXT.
+
 2020-04-23 Iain Sandoe <iain@sandoe.co.uk>
 
        PR c++/94288

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 2fe7b66..66308a2 100644 (file)
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -390,7 +390,12 @@ template_class_depth (tree type)
        ++depth;
 
       if (DECL_P (type))
-       type = CP_DECL_CONTEXT (type);
+       {
+         if (tree fctx = DECL_FRIEND_CONTEXT (type))
+           type = fctx;
+         else
+           type = CP_DECL_CONTEXT (type);
+       }
       else if (LAMBDA_TYPE_P (type) && LAMBDA_TYPE_EXTRA_SCOPE (type))
        type = LAMBDA_TYPE_EXTRA_SCOPE (type);
       else

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f9ab061..e0df5bc 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-04-23  Patrick Palka  <ppalka@redhat.com>
+
+       PR c++/94645
+       * g++.dg/cpp2a/concepts-lambda6.C: New test.
+
 2019-04-23  Eric Botcazou  <ebotcazou@adacore.com>
 
        * g++.dg/opt/store-merging-4.C: New test.

diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda6.C b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda6.C
new file mode 100644 (file)
index 0000000..0b7c045
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda6.C
@@ -0,0 +1,19 @@
+// PR c++/94645
+// { dg-do compile { target concepts } }
+
+struct unordered_map {
+  int cend() const noexcept;
+};
+
+template <typename a> concept HasMapInterface = requires(a t) { t.cend(); };
+
+template <typename Mapper> requires HasMapInterface<decltype(Mapper::map())>
+struct l {
+  friend void foo(l opt) { ([]() {})(); }
+};
+
+struct p {
+  static unordered_map map();
+};
+
+void g(l<p> *y) { foo(*y); }