[PATCH] c++: SFINAE for invalid delete-expression [PR79706]

[Patrick Palka via Gcc-patches]

This fixes SFINAE when substitution yields an invalid delete-expression
due to the pertinent deallocation function being marked deleted or
otherwise inaccessible.

We need to check for an erroneous result from build_op_delete_call and
exit early in that case, so that we don't build a COND_EXPR around the
erroneous call which finish_decltype_type would then quietly accept.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK to
commit?

gcc/cp/ChangeLog:

        PR c++/79706
        * init.c (build_vec_delete_1): Return error_mark_node if
        deallocate_expr is error_mark_node.
        (build_delete): Return error_mark_node if do_delete is
        error_mark_node.

gcc/testsuite/ChangeLog:

        PR c++/79706
        * g++.dg/template/sfinae30.C: New test.
---
 gcc/cp/init.c                            |  8 ++++++--
 gcc/testsuite/g++.dg/template/sfinae30.C | 21 +++++++++++++++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/template/sfinae30.C

diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index e2e547afd96..c1047dbb1cc 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -4076,7 +4076,9 @@ build_vec_delete_1 (location_t loc, tree base, tree 
maxindex, tree type,
     }
 
   body = loop;
-  if (!deallocate_expr)
+  if (deallocate_expr == error_mark_node)
+    return error_mark_node;
+  else if (!deallocate_expr)
     ;
   else if (!body)
     body = deallocate_expr;
@@ -4993,7 +4995,9 @@ build_delete (location_t loc, tree otype, tree addr,
       return expr;
     }
 
-  if (do_delete)
+  if (do_delete == error_mark_node)
+    return error_mark_node;
+  else if (do_delete)
     {
       tree do_delete_call_expr = extract_call_expr (do_delete);
       if (TREE_CODE (do_delete_call_expr) == CALL_EXPR)
diff --git a/gcc/testsuite/g++.dg/template/sfinae30.C 
b/gcc/testsuite/g++.dg/template/sfinae30.C
new file mode 100644
index 00000000000..82f31aaa625
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/sfinae30.C
@@ -0,0 +1,21 @@
+// PR c++/79706
+// { dg-do compile { target c++11 } }
+
+struct A {
+  void operator delete(void*) = delete;
+private:
+  void operator delete[](void*);
+};
+
+extern A *p;
+
+template<typename T>
+auto foo(T *t) -> decltype(delete t); // { dg-error "use of deleted function" }
+
+template<typename T>
+auto bar(T *t) -> decltype(delete[] t); // { dg-error "private within this 
context" }
+
+void baz() {
+  foo<A>(p); // { dg-error "no match" }
+  bar<A>(p); // { dg-error "no match" }
+}
-- 
2.26.2.561.g07d8ea56f2