On 17 Jan 2025, at 0:12, Jason Merrill wrote:
> On 1/5/25 11:19 AM, Simon Martin wrote:
>> We currently reject the following code
>>
>> === code here ===
>> template <int non_template> struct S { friend class non_template; };
>> class non_template {};
>> S<0> s;
>> === code here ===
>>
>> While EDG agrees with the current behaviour, clang and MSVC don't
>> (see
>> https://godbolt.org/z/69TGaabhd), and I believe that this code is
>> valid,
>> since the friend clause does not actually declare a type, so it
>> cannot
>> shadow anything. The fact that we didn't error out if the
>> non_template
>> class was declared before S backs this up as well.
>>
>> This patch fixes this by skipping the call to check_template_shadow
>> for
>> hidden bindings.
>
> OK.
Thanks Jason. Since it’s a regression from GCC 8, OK as well for
active branches?
Simon
>> Successfully tested on x86_64-pc-linux-gnu.
>>
>> PR c++/118255
>>
>> gcc/cp/ChangeLog:
>>
>> * name-lookup.cc (pushdecl): Don't call check_template_shadow
>> for hidden bindings.
>>
>> gcc/testsuite/ChangeLog:
>>
>> * g++.dg/lookup/pr99116-1.C: Adjust test expectation.
>> * g++.dg/template/friend84.C: New test.
>>
>> ---
>> gcc/cp/name-lookup.cc | 5 ++++-
>> gcc/testsuite/g++.dg/lookup/pr99116-1.C | 2 +-
>> gcc/testsuite/g++.dg/template/friend84.C | 26
>> ++++++++++++++++++++++++
>> 3 files changed, 31 insertions(+), 2 deletions(-)
>> create mode 100644 gcc/testsuite/g++.dg/template/friend84.C
>>
>> diff --git a/gcc/cp/name-lookup.cc b/gcc/cp/name-lookup.cc
>> index 0e185d3ef42..d1abb205bc7 100644
>> --- a/gcc/cp/name-lookup.cc
>> +++ b/gcc/cp/name-lookup.cc
>> @@ -4040,7 +4040,10 @@ pushdecl (tree decl, bool hiding)
>> if (old && anticipated_builtin_p (old))
>> old = OVL_CHAIN (old);
>> - check_template_shadow (decl);
>> + if (hiding)
>> + ; /* Hidden bindings don't shadow anything. */
>> + else
>> + check_template_shadow (decl);
>> if (DECL_DECLARES_FUNCTION_P (decl))
>> {
>> diff --git a/gcc/testsuite/g++.dg/lookup/pr99116-1.C
>> b/gcc/testsuite/g++.dg/lookup/pr99116-1.C
>> index 01b483ea915..efee3e4aca3 100644
>> --- a/gcc/testsuite/g++.dg/lookup/pr99116-1.C
>> +++ b/gcc/testsuite/g++.dg/lookup/pr99116-1.C
>> @@ -2,7 +2,7 @@
>> template<int T> struct Z {
>> - friend struct T; // { dg-error "shadows template parameter" }
>> + friend struct T; // { dg-bogus "shadows template parameter" }
>> };
>> struct Y {
>> diff --git a/gcc/testsuite/g++.dg/template/friend84.C
>> b/gcc/testsuite/g++.dg/template/friend84.C
>> new file mode 100644
>> index 00000000000..64ea41a552b
>> --- /dev/null
>> +++ b/gcc/testsuite/g++.dg/template/friend84.C
>> @@ -0,0 +1,26 @@
>> +// PR c++/118255
>> +// { dg-do "compile" }
>> +
>> +// The PR's case, that used to error out.
>> +template <int non_template>
>> +struct S {
>> + friend class non_template; // { dg-bogus "shadows template
>> parameter" }
>> +};
>> +
>> +class non_template {};
>> +S<0> s;
>> +
>> +// We already accepted cases where the friend is already declared.
>> +template <int non_template>
>> +struct T {
>> + friend class non_template;
>> +};
>> +T<0> t;
>> +
>> +// We should reject (re)declarations.
>> +template <int non_template>
>> +struct U {
>> + class non_template {}; // { dg-error "shadows template parameter"
>> }
>> + void non_template () {} // { dg-error "shadows template parameter"
>> }
>> +};
>> +U<0> u;
