Re: [PATCH] c++: non-standalone surrogate call template

[Jason Merrill via Gcc-patches]

On 7/12/23 14:47, Patrick Palka wrote:

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?  There might be an existing PR for this issue but Bugzilla search
seems to be timing out for me currently.

OK.

-- >8 --

I noticed we were accidentally preventing ourselves from considering
a pointer/reference-to-function conversion function template if it's
not the first conversion function that's considered, which for the
testcase below resulted in us accepting the B call but not the A call
despite the only difference between A and B being the order of member
declarations.  This patch fixes this so that the outcome of overload
resolution doesn't arbitrarily depend on declaration order in this
situation.

gcc/cp/ChangeLog:

        * call.cc (add_template_conv_candidate): Don't check for
        non-empty 'candidates' here.
        (build_op_call): Check it here, before we've considered any
        conversion functions.

gcc/testsuite/ChangeLog:

        * g++.dg/overload/conv-op5.C: New test.
---
  gcc/cp/call.cc                           | 24 ++++++++++++++----------
  gcc/testsuite/g++.dg/overload/conv-op5.C | 18 ++++++++++++++++++
  2 files changed, 32 insertions(+), 10 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/overload/conv-op5.C

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 81935b83908..119063979fa 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -3709,12 +3709,6 @@ add_template_conv_candidate (struct z_candidate 
**candidates, tree tmpl,
                             tree return_type, tree access_path,
                             tree conversion_path, tsubst_flags_t complain)
  {
-  /* Making this work broke PR 71117 and 85118, so until the committee resolves
-     core issue 2189, let's disable this candidate if there are any call
-     operators.  */
-  if (*candidates)
-    return NULL;
-
    return
      add_template_candidate_real (candidates, tmpl, NULL_TREE, NULL_TREE,
                                 NULL_TREE, arglist, return_type, access_path,
@@ -5290,6 +5284,8 @@ build_op_call (tree obj, vec<tree, va_gc> **args, 
tsubst_flags_t complain)
                      LOOKUP_NORMAL, &candidates, complain);
      }

+ bool any_call_ops = candidates != nullptr;

+
    convs = lookup_conversions (type);

for (; convs; convs = TREE_CHAIN (convs))

@@ -5306,10 +5302,18 @@ build_op_call (tree obj, vec<tree, va_gc> **args, 
tsubst_flags_t complain)
              continue;

if (TREE_CODE (fn) == TEMPLATE_DECL)

-             add_template_conv_candidate
-               (&candidates, fn, obj, *args, totype,
-                /*access_path=*/NULL_TREE,
-                /*conversion_path=*/NULL_TREE, complain);
+             {
+               /* Making this work broke PR 71117 and 85118, so until the
+                  committee resolves core issue 2189, let's disable this
+                  candidate if there are any call operators.  */
+               if (any_call_ops)
+                 continue;
+
+               add_template_conv_candidate
+                 (&candidates, fn, obj, *args, totype,
+                  /*access_path=*/NULL_TREE,
+                  /*conversion_path=*/NULL_TREE, complain);
+             }
            else
              add_conv_candidate (&candidates, fn, obj,
                                  *args, /*conversion_path=*/NULL_TREE,
diff --git a/gcc/testsuite/g++.dg/overload/conv-op5.C 
b/gcc/testsuite/g++.dg/overload/conv-op5.C
new file mode 100644
index 00000000000..b7724908b62
--- /dev/null
+++ b/gcc/testsuite/g++.dg/overload/conv-op5.C
@@ -0,0 +1,18 @@
+// { dg-do compile { target c++11 } }
+
+template<class T> using F = int(*)(T);
+using G = int(*)(int*);
+
+struct A {
+  template<class T> operator F<T>();  // #1
+  operator G() = delete; // #2
+};
+
+int i = A{}(0); // selects #1
+
+struct B {
+  operator G() = delete; // #2
+  template<class T> operator F<T>();  // #1
+};
+
+int j = B{}(0); // selects #1