On 29 Jun 2024, at 0:00, Patrick Palka wrote:
> On Fri, 28 Jun 2024, Simon Martin wrote:
>
>> We currently ICE when emitting the error message for this invalid
>> code:
>>
>> === cut here ===
>> struct foo {
>> template<int> void not_const() {}
>> };
>> void fn(const foo& obj) {
>> obj.not_const<5>();
>> }
>> === cut here ===
>>
>> The problem is that get_fndecl_argument_location assumes that it has
>> a
>> FUNCTION_DECL in its hands to find the location of the bad argument.
>> It might
>> however have a TEMPLATE_DECL if there's a single candidate that
>> cannot be
>> instantiated, like here.
>>
>> This patch simply defaults to using the FNDECL's location in this
>> case, which
>> fixes this PR.
>>
>> Successfully tested on x86_64-pc-linux-gnu.
>>
>> PR c++/115364
>>
>> gcc/cp/ChangeLog:
>>
>> * call.cc (get_fndecl_argument_location): Use FNDECL's location for
>> TEMPLATE_DECLs.
>>
>> gcc/testsuite/ChangeLog:
>>
>> * g++.dg/overload/template7.C: New test.
>>
>> ---
>> gcc/cp/call.cc | 4 ++++
>> gcc/testsuite/g++.dg/overload/template7.C | 9 +++++++++
>> 2 files changed, 13 insertions(+)
>> create mode 100644 gcc/testsuite/g++.dg/overload/template7.C
>>
>> diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
>> index 7bbc1fb0c78..d5ff2311e63 100644
>> --- a/gcc/cp/call.cc
>> +++ b/gcc/cp/call.cc
>> @@ -8347,6 +8347,10 @@ get_fndecl_argument_location (tree fndecl, int
>> argnum)
>> if (DECL_ARTIFICIAL (fndecl))
>> return DECL_SOURCE_LOCATION (fndecl);
>>
>> + /* Use FNDECL's location for TEMPLATE_DECLs. */
>> + if (TREE_CODE (fndecl) == TEMPLATE_DECL)
>> + return DECL_SOURCE_LOCATION (fndecl);
>> +
>
> For TEMPLATE_DECL fndecl, it'd be more natural to return the
> corresponding argument location of its DECL_TEMPLATE_RESULT (which
> should be a FUNCTION_DECL). The STRIP_TEMPLATE macro would be
> convenient to use here.
>
>
> It seems this doesn't fix the regression completely however because
> in GCC 11 the code was rejected with a "permerror" (which can be
> downgraded to a warning with -fpermissive):
>
> 115364.C: In function ‘void fn(const foo&)’:
> 115364.C:5:43: error: passing ‘const foo’ as ‘this’ argument
> discards qualifiers [-fpermissive]
> 5 | void fn(const foo& obj) { obj.not_const<5>(); }
> | ~~~~~~~~~~~~~~~~^~
> 115364.C:3:24: note: in call to ‘void foo::not_const() [with int
> <anonymous> = 5]’
> 3 | template<int> void not_const() {}
> | ^~~~~~~~~
>
> and we now reject with an ordinary error:
>
> 115364.C: In function ‘void fn(const foo&)’:
> 115364.C:5:27: error: cannot convert ‘const foo*’ to ‘foo*’
> 5 | void fn(const foo& obj) { obj.not_const<5>(); }
> | ^~~
> | |
> | const foo*
> 115364.C:3:24: note: initializing argument 'this' of
> ‘template<int <anonymous> > void foo::not_const()’
> 3 | template<int> void not_const() {}
> | ^~~~~~~~~
>
> To restore the error into a permerror, we need to figure out why we're
> unexpectedly hitting this code path with a TEMPLATE_DECL, and why it's
> necessary that the member function needs to take no arguments. It
> turns
> out I looked into this and submitted a patch for PR106760 (of which
> this
> PR115364 is a dup) last year:
> https://gcc.gnu.org/pipermail/gcc-patches/2023-June/620514.html
>
> The patch was approved, but I lost track of it and never pushed it :/
> I'm going to go ahead and push that fix shortly, sorry for not doing
> so
> earlier. Thanks for looking into this issue!
Sounds good, thanks!
>
>> int i;
>> tree param;
>>
>> diff --git a/gcc/testsuite/g++.dg/overload/template7.C
>> b/gcc/testsuite/g++.dg/overload/template7.C
>> new file mode 100644
>> index 00000000000..67191c4ff62
>> --- /dev/null
>> +++ b/gcc/testsuite/g++.dg/overload/template7.C
>> @@ -0,0 +1,9 @@
>> +// PR c++/115364
>> +// { dg-do compile }
>> +
>> +struct foo {
>> + template<int> void not_const() {} // { dg-note "initializing" }
>> +};
>> +void fn(const foo& obj) {
>> + obj.not_const<5>(); // { dg-error "cannot convert" }
>> +}
>> --
>> 2.44.0
>>
>>
>>
>>
