Hi again, hi Jason,
I can't help further investigating this issue and I have a completely
different proposal which pursues a different hint of Jason: why the
TREE_TYPE of such DECL is error_mark_node in the first place? As we
understand now that is just something that start_decl_1 does when it
sees an incomplete type. Then why we have that kind of type? The answer
is this change, back in 2006 (!), for c++/27952:
https://gcc.gnu.org/ml/gcc-patches/2006-10/msg00862.html
which changed the loop in xref_basetypes to early return false after
error. That implies that the caller skips the body, the type remains
incomplete. That has non trivial implications: we avoid ICEs but we also
end up with redundant error messages about incomplete types during error
recovery. And the inconsistencies shown by the present issue. Thus my
idea: let's fix that old bug in a different, lighter way and revert the
bulk of the old fix, just disregard and continue on the erroneous
duplicate bases in the main xref_basetpes loop. I think at some point
Jason hinted at that as a general error recovery strategy: we have been
doing exactly that until 2006!!
In a sense we are also back to my original idea of not zeroing by hand
the type in cp_parser_class_head.
Anyway, things appear to work fine: no regressions, more terse
diagnostic, see inherit/crash6.C but also the tweaked
g++.dg/inherit/virtual1.C (now the diagnostic is *very* similar to that
produced by clang, by the way, eh, eh) and the new
g++.dg/inherit/union2.C, no redundant error messages on the declaration
of u during error recovery.
The remaining issue to be discussed is what to do about that old bug,
c++/27952, a crash in decay_conversion during error recovery, when vtt
is found null. I propose to simply check for it in
build_special_member_call, avoid passing an unusable null argument to
decay_conversion and return back an error_mark_node. We could also do
gcc_assert (seen_error()) before returning error_mark_node?
Ah, there is also another detail: around line 12930 of the decl.c diff,
I'm also reverting my own 2010 changes to fix c++/30298 (r159637) which
really had to do with the 2006 change as well: we can have the
gcc_assert back and still handle correctly inherit/crash1 and crash2
which I added back then. This is nice, I think.
In conclusion, IMHO this approach is way better than all the other I
tried so far, modulo the possible need of additional / better error
recovery measures in build_special_member_call, etc.
Thanks,
Paolo.
////////////////////////////
Index: cp/call.c
===================================================================
--- cp/call.c (revision 237318)
+++ cp/call.c (working copy)
@@ -8022,6 +8022,8 @@ build_special_member_call (tree instance, tree nam
or destructor, then we fetch the VTT directly.
Otherwise, we look it up using the VTT we were given. */
vtt = DECL_CHAIN (CLASSTYPE_VTABLES (current_class_type));
+ if (!vtt)
+ return error_mark_node;
vtt = decay_conversion (vtt, complain);
if (vtt == error_mark_node)
return error_mark_node;
Index: cp/cp-tree.h
===================================================================
--- cp/cp-tree.h (revision 237318)
+++ cp/cp-tree.h (working copy)
@@ -5771,7 +5771,7 @@ extern int grok_ctor_properties
(const_tree, con
extern bool grok_op_properties (tree, bool);
extern tree xref_tag (enum tag_types, tree,
tag_scope, bool);
extern tree xref_tag_from_type (tree, tree, tag_scope);
-extern bool xref_basetypes (tree, tree);
+extern void xref_basetypes (tree, tree);
extern tree start_enum (tree, tree, tree, tree, bool,
bool *);
extern void finish_enum_value_list (tree);
extern void finish_enum (tree);
Index: cp/decl.c
===================================================================
--- cp/decl.c (revision 237318)
+++ cp/decl.c (working copy)
@@ -12871,12 +12871,9 @@ xref_tag_from_type (tree old, tree id, tag_scope s
/* Create the binfo hierarchy for REF with (possibly NULL) base list
BASE_LIST. For each element on BASE_LIST the TREE_PURPOSE is an
access_* node, and the TREE_VALUE is the type of the base-class.
- Non-NULL TREE_TYPE indicates virtual inheritance.
-
- Returns true if the binfo hierarchy was successfully created,
- false if an error was detected. */
+ Non-NULL TREE_TYPE indicates virtual inheritance. */
-bool
+void
xref_basetypes (tree ref, tree base_list)
{
tree *basep;
@@ -12889,7 +12886,7 @@ xref_basetypes (tree ref, tree base_list)
tree igo_prev; /* Track Inheritance Graph Order. */
if (ref == error_mark_node)
- return false;
+ return;
/* The base of a derived class is private by default, all others are
public. */
@@ -12933,11 +12930,7 @@ xref_basetypes (tree ref, tree base_list)
/* The binfo slot should be empty, unless this is an (ill-formed)
redefinition. */
- if (TYPE_BINFO (ref) && !TYPE_SIZE (ref))
- {
- error ("redefinition of %q#T", ref);
- return false;
- }
+ gcc_assert (!TYPE_BINFO (ref) || TYPE_SIZE (ref));
gcc_assert (TYPE_MAIN_VARIANT (ref) == ref);
@@ -12957,10 +12950,7 @@ xref_basetypes (tree ref, tree base_list)
CLASSTYPE_NON_AGGREGATE (ref) = 1;
if (TREE_CODE (ref) == UNION_TYPE)
- {
- error ("derived union %qT invalid", ref);
- return false;
- }
+ error ("derived union %qT invalid", ref);
}
if (max_bases > 1)
@@ -12968,7 +12958,7 @@ xref_basetypes (tree ref, tree base_list)
if (TYPE_FOR_JAVA (ref))
{
error ("Java class %qT cannot have multiple bases", ref);
- return false;
+ return;
}
else
warning (OPT_Wmultiple_inheritance,
@@ -12982,7 +12972,7 @@ xref_basetypes (tree ref, tree base_list)
if (TYPE_FOR_JAVA (ref))
{
error ("Java class %qT cannot have virtual bases", ref);
- return false;
+ return;
}
else if (max_dvbases)
warning (OPT_Wvirtual_inheritance,
@@ -13006,7 +12996,7 @@ xref_basetypes (tree ref, tree base_list)
{
error ("base type %qT fails to be a struct or class type",
basetype);
- return false;
+ continue;
}
if (TYPE_FOR_JAVA (basetype) && (current_lang_depth () == 0))
@@ -13040,7 +13030,7 @@ xref_basetypes (tree ref, tree base_list)
error ("recursive type %qT undefined", basetype);
else
error ("duplicate base type %qT invalid", basetype);
- return false;
+ continue;
}
if (PACK_EXPANSION_P (TREE_VALUE (base_list)))
@@ -13088,8 +13078,6 @@ xref_basetypes (tree ref, tree base_list)
else
break;
}
-
- return true;
}
Index: cp/parser.c
===================================================================
--- cp/parser.c (revision 237318)
+++ cp/parser.c (working copy)
@@ -22050,9 +22050,8 @@ cp_parser_class_head (cp_parser* parser,
/* If we're really defining a class, process the base classes.
If they're invalid, fail. */
- if (type && cp_lexer_next_token_is (parser->lexer, CPP_OPEN_BRACE)
- && !xref_basetypes (type, bases))
- type = NULL_TREE;
+ if (type && cp_lexer_next_token_is (parser->lexer, CPP_OPEN_BRACE))
+ xref_basetypes (type, bases);
done:
/* Leave the scope given by the nested-name-specifier. We will
Index: testsuite/g++.dg/inherit/crash6.C
===================================================================
--- testsuite/g++.dg/inherit/crash6.C (revision 0)
+++ testsuite/g++.dg/inherit/crash6.C (working copy)
@@ -0,0 +1,10 @@
+// PR c++/70202
+
+class A
+{
+ virtual void foo () { }
+};
+class B : public A, A { }; // { dg-error "duplicate base type" }
+
+B b1, &b2 = b1;
+A a = b2;
Index: testsuite/g++.dg/inherit/union2.C
===================================================================
--- testsuite/g++.dg/inherit/union2.C (revision 0)
+++ testsuite/g++.dg/inherit/union2.C (working copy)
@@ -0,0 +1,3 @@
+struct A { };
+union U : A { }; // { dg-error "derived union 'U' invalid" }
+U u;
Index: testsuite/g++.dg/inherit/virtual1.C
===================================================================
--- testsuite/g++.dg/inherit/virtual1.C (revision 237318)
+++ testsuite/g++.dg/inherit/virtual1.C (working copy)
@@ -5,8 +5,8 @@ struct A
virtual ~A() {}
};
-struct B : A, virtual A {}; // { dg-error "duplicate base|forward
declaration" }
+struct B : A, virtual A {}; // { dg-error "duplicate base" }
-struct C : A, B {}; // { dg-error "duplicate base|invalid use" }
+struct C : A, B {}; // { dg-message "direct base 'A' inaccessible"
}
-C c; // { dg-error "aggregate" }
+C c;
