[gcc/devel/ranger] c++: Parenthesized-init of aggregates accepts invalid code [PR94885]

[Aldy Hernandez]

https://gcc.gnu.org/g:30da2906ac521749aef8260fc1d942e62073f19d

commit 30da2906ac521749aef8260fc1d942e62073f19d
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Apr 30 11:36:17 2020 -0400

    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:
---
 gcc/cp/ChangeLog                          |  6 ++++++
 gcc/cp/typeck2.c                          |  6 +++++-
 gcc/testsuite/ChangeLog                   |  5 +++++
 gcc/testsuite/g++.dg/cpp2a/paren-init26.C | 14 ++++++++++++++
 4 files changed, 30 insertions(+), 1 deletion(-)

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" }
+}