From: Marek Polacek <polacek@redhat.com>
Date: Thu, 30 Apr 2020 15:36:17 +0000 (-0400)
Subject: c++: Parenthesized-init of aggregates accepts invalid code [PR94885]
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=30da2906ac521749aef8260fc1d942e62073f19d;p=gcc.git

c++: Parenthesized-init of aggregates accepts invalid code [PR94885]

Here we have (conceptually *) something like

  struct B { };
  struct D : B { };
  D(0); // invalid

and in C++20 the ()-initialization has created a { 0 } constructor that
it tries to initialize an object of type D with.  We should reject
initializing an object of type B from 0, but we wrongly accept it because
process_init_constructor_record skips initializers for empty bases/fields:
       if (DECL_SIZE (field) && integer_zerop (DECL_SIZE (field))
           && !TREE_SIDE_EFFECTS (next))
         /* Don't add trivial initialization of an empty base/field to the
            constructor, as they might not be ordered the way the back-end
            expects.  */
         continue;
but here 'next' was error_mark_node, returned by massage_elt_init, so we
wound up with { } which would validly value-initialize the object.

[*] Usually digest_init in build_new_method_call_1 would detect this,
but in this case the instance is is_dummy_object and we don't call
digest just yet.

	PR c++/94885
	* typeck2.c (process_init_constructor_record): Return PICFLAG_ERRONEOUS
	if an initializer element was erroneous.

	* g++.dg/cpp2a/paren-init26.C: New test.
---

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 0675f982677..0b6b0ee2f5f 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2020-05-01  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/94885
+	* typeck2.c (process_init_constructor_record): Return PICFLAG_ERRONEOUS
+	if an initializer element was erroneous.
+
 2020-05-01  Jason Merrill  <jason@redhat.com>
 
 	PR c++/90479
diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c
index 56fd9bafa7e..9e5d145a6cd 100644
--- a/gcc/cp/typeck2.c
+++ b/gcc/cp/typeck2.c
@@ -1661,7 +1661,11 @@ process_init_constructor_record (tree type, tree init, int nested, int flags,
 	      ++idx;
 	    }
 	}
-      if (next)
+      if (next == error_mark_node)
+	/* We skip initializers for empty bases/fields, so skipping an invalid
+	   one could make us accept invalid code.  */
+	return PICFLAG_ERRONEOUS;
+      else if (next)
 	/* Already handled above.  */;
       else if (DECL_INITIAL (field))
 	{
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 949b81a4392..997ef8d091c 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-05-01  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/94885
+	* g++.dg/cpp2a/paren-init26.C: New test.
+
 2020-05-01  Andreas Tobler  <andreast@gcc.gnu.org>
 
 	* gcc.dg/asan/pr87930.c: Enable on x86_64 FreeBSD.
diff --git a/gcc/testsuite/g++.dg/cpp2a/paren-init26.C b/gcc/testsuite/g++.dg/cpp2a/paren-init26.C
new file mode 100644
index 00000000000..0b98ebf43bb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/paren-init26.C
@@ -0,0 +1,14 @@
+// PR c++/94885 - paren-init of aggregates accepts invalid code.
+// { dg-do compile { target c++2a } }
+
+template <typename T, typename = decltype(T(0))> // { dg-error "could not convert" }
+void foo();
+
+struct base {};
+struct derived : base {};
+
+void
+bar()
+{
+  foo<derived>(); // { dg-error "no matching function" }
+}