Re: C++ PATCH for c++/81236, missed 'this' capture with template-id in generic lambda

[Jason Merrill <jason at redhat dot com>]

On Tue, Aug 29, 2017 at 5:37 PM, Jason Merrill <jason@redhat.com> wrote:
> We could approach this by extending that change to all generic
> lambdas, and that might be appropriate for GCC 7, but it seems to me
> that this approach will just mean any problems with doing all the
> normal processing in a template will remain latent until someone
> happens to use them in a generic lambda; instead, this patch removes
> the template special case and fixes the normal code to work properly
> in templates.

I noticed today that this caused a regression on the attached
testcases, because we weren't updating the type of the BASELINK after
instantiating the auto function.

Tested x86_64-pc-linux-gnu, applying to trunk.

commit d1d91f146d88b9d7442cce1e03edca55693de139
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Mar 14 16:27:08 2018 -0400

            PR c++/81236 - auto variable and auto function
    
            * pt.c (tsubst_baselink): Update the type of the BASELINK after
            mark_used.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 14321816cde..2ea5fc79a2c 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -14700,9 +14700,16 @@ tsubst_baselink (tree baselink, tree object_type,
   /* If lookup found a single function, mark it as used at this point.
      (If lookup found multiple functions the one selected later by
      overload resolution will be marked as used at that point.)  */
-  if (!template_id_p && !really_overloaded_fn (fns)
-      && !mark_used (OVL_FIRST (fns), complain) && !(complain & tf_error))
-    return error_mark_node;
+  if (!template_id_p && !really_overloaded_fn (fns))
+    {
+      tree fn = OVL_FIRST (fns);
+      bool ok = mark_used (fn, complain);
+      if (!ok && !(complain & tf_error))
+	return error_mark_node;
+      if (ok && BASELINK_P (baselink))
+	/* We might have instantiated an auto function.  */
+	TREE_TYPE (baselink) = TREE_TYPE (fn);
+    }
 
   if (BASELINK_P (baselink))
     {
diff --git a/gcc/testsuite/g++.dg/cpp1y/auto-fn48.C b/gcc/testsuite/g++.dg/cpp1y/auto-fn48.C
new file mode 100644
index 00000000000..bf9448e793e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/auto-fn48.C
@@ -0,0 +1,15 @@
+// { dg-do compile { target c++14 } }
+
+template <class T> struct A
+{
+  static auto fn() { }
+  static void f()
+  {
+    auto x = fn;
+  }
+};
+
+int main()
+{
+  A<int>::f();
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/auto-fn49.C b/gcc/testsuite/g++.dg/cpp1y/auto-fn49.C
new file mode 100644
index 00000000000..d2e490604a7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/auto-fn49.C
@@ -0,0 +1,12 @@
+// CWG issue 2335
+// { dg-do compile { target c++14 } }
+
+template <class... Ts> struct partition_indices {
+  static auto compute_right () {}
+  static constexpr auto right = compute_right;
+};
+auto foo () -> partition_indices<>;
+void f() {
+  auto x = foo();
+  auto y = x.right;
+}