On 1/31/25 11:12 AM, Simon Martin wrote:
Hi Jason,
On 31 Jan 2025, at 16:29, Jason Merrill wrote:
On 1/31/25 9:52 AM, Simon Martin wrote:
Hi Jason,
On 9 Jan 2025, at 22:55, Jason Merrill wrote:
On 1/9/25 8:25 AM, Simon Martin wrote:
We segfault upon the following invalid code
=== cut here ===
template <int> struct S {
friend void foo (int a = []{}());
};
void foo (int a) {}
int main () {
S<0> t;
foo ();
}
=== cut here ===
The problem is that we end up with a LAMBDA_EXPR callee in
set_flags_from_callee, and dereference its NULL_TREE
TREE_TYPE (TREE_TYPE ( )).
This patch simply sets the default argument to error_mark_node for
friend functions that do not meet the requirement in C++17
11.3.6/4.
Successfully tested on x86_64-pc-linux-gnu.
PR c++/118319
gcc/cp/ChangeLog:
* decl.cc (grokfndecl): Inspect all friend function parameters,
and set them to error_mark_node if invalid.
gcc/testsuite/ChangeLog:
* g++.dg/parse/defarg18.C: New test.
---
gcc/cp/decl.cc | 13 +++++---
gcc/testsuite/g++.dg/parse/defarg18.C | 48
+++++++++++++++++++++++++++
2 files changed, 57 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/parse/defarg18.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 503ecd9387e..b2761c23d3e 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -11134,14 +11134,19 @@ grokfndecl (tree ctype,
expression, that declaration shall be a definition..." */
if (friendp && !funcdef_flag)
{
+ bool has_permerrored = false;
for (tree t = FUNCTION_FIRST_USER_PARMTYPE (decl);
t && t != void_list_node; t = TREE_CHAIN (t))
if (TREE_PURPOSE (t))
{
- permerror (DECL_SOURCE_LOCATION (decl),
- "friend declaration of %qD specifies default "
- "arguments and isn%'t a definition", decl);
- break;
+ if (!has_permerrored)
+ {
+ has_permerrored = true;
+ permerror (DECL_SOURCE_LOCATION (decl),
+ "friend declaration of %qD specifies default "
+ "arguments and isn%'t a definition", decl);
+ }
+ TREE_PURPOSE (t) = error_mark_node;
If we're going to unconditionally change TREE_PURPOSE, then
permerror
needs to strengthen to error. But I'd think we could leave the
current state in a non-template class, only changing the template
case.
Thanks. It’s true that setting the argument to error_mark_node is
contradictory with the fact that we accept the code with
-fpermissive,
even if only under processing_template_decl, so I checked if
there’s
not a better way of approaching this PR.
After a bit of investigation, I think that the real problem is that
duplicate_decls tries to merge the two declarations, even though they
don’t meet the constraint about friend functions and default
arguments.
I disagree; in this testcase the friend is the (lexically) first
declaration, the problem is that it's a non-defining friend (in a
template) that specifies default args, as addressed by your first
patch.
Fair.
I still think my earlier comments are the way forward here: leave the
non-template case alone (permerror, don't change TREE_PURPOSE), in a
template give a hard error and change to error_mark_node.
Thanks, understood. The reason I looked for another “solution” is
that it felt strange to be permissive in non-templates and stricter in
templates. For example, if we do so, we’ll regress the case I added in
defarg19.C in -fpermissive (also available at
https://godbolt.org/z/YT3dexGjM).
I’m probably splitting hair, and I’m happy to go ahead with your
suggestion if you think it’s fine. Otherwise I’ll see if I find some
better fix.
That's fine, it's common to be stricter in templates.
Jason
