Hi Jason,
On 4 Feb 2025, at 1:11, Jason Merrill wrote:
> 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.
Ok, cool. The attached updated patch does this, and has been
successfully tested on x86_64-pc-linux-gnu. OK for trunk?
Thanks, Simon
From bfa8949814b15d1c143b0928e8fbb7741bb93ac3 Mon Sep 17 00:00:00 2001
From: Simon Martin <si...@nasilyan.com>
Date: Tue, 4 Feb 2025 11:17:35 +0100
Subject: [PATCH] c++: Reject default arguments for template class friend
functions [PR118319]
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 sets the default argument to error_mark_node for template
class friend functions that do not meet the requirement in C++17
11.3.6/4 (the change is restricted to templates per discussion with
Jason).
Successfully tested on x86_64-pc-linux-gnu.
PR c++/118319
gcc/cp/ChangeLog:
* decl.cc (grokfndecl): Inspect all friend function parameters.
Set their default value to error_mark_node if processing a
template and it's not valid for them to have any.
gcc/testsuite/ChangeLog:
* g++.dg/parse/defarg18.C: New test.
---
gcc/cp/decl.cc | 14 +++++---
gcc/testsuite/g++.dg/parse/defarg18.C | 48 +++++++++++++++++++++++++++
2 files changed, 58 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 b7af33b3231..d9c79e6f620 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -11213,14 +11213,20 @@ 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);
+ }
+ if (processing_template_decl)
+ TREE_PURPOSE (t) = error_mark_node;
}
}
diff --git a/gcc/testsuite/g++.dg/parse/defarg18.C
b/gcc/testsuite/g++.dg/parse/defarg18.C
new file mode 100644
index 00000000000..62c8f15f284
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/defarg18.C
@@ -0,0 +1,48 @@
+// PR c++/118319
+// { dg-do "compile" { target c++11 } }
+
+// Template case, that used to crash.
+
+template <int>
+struct S {
+ friend void foo1 (int a = []{}()); // { dg-error "specifies default|only
declaration" }
+ friend void foo3 (int a, // { dg-error "specifies default|only
declaration" }
+ int b = []{}(),
+ int c = []{}());
+};
+
+void foo1 (int a) {}
+void foo3 (int a, int b, int c) {}
+
+void hello (){
+ S<0> t;
+ foo1 ();
+ foo3 (1, 2);
+}
+
+
+// Template case, that already worked.
+
+template <int>
+struct T {
+ friend void bar (int a = []{}()); // { dg-error "specifies default|only
declaration" }
+};
+
+void hallo (){
+ T<0> t;
+ bar (); // { dg-error "not declared" }
+}
+
+
+// Non template case, that already worked.
+
+struct NoTemplate {
+ friend void baz (int a = []{}()); // { dg-error "specifies default|could not
convert" }
+};
+
+void baz (int a) {} // { dg-error "only declaration" }
+
+void ola (){
+ NoTemplate t;
+ baz (); // { dg-error "void value not ignored" }
+}
--
2.44.0
