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

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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.
This commit is contained in:
Marek Polacek 2020-04-30 11:36:17 -04:00
parent 13ec6724cd
commit 30da2906ac
4 changed files with 30 additions and 1 deletions
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6
gcc/cp/ChangeLog
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@ -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

6
gcc/cp/typeck2.c
View File

@ -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))
{

5
gcc/testsuite/ChangeLog
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@ -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.

14
gcc/testsuite/g++.dg/cpp2a/paren-init26.C Normal file
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@ -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" }
}