* Patrick Palka <ppa...@redhat.com> [2025-02-28 10:37:37]:
> Hi,
>
> On Fri, 28 Feb 2025, Da Xie wrote:
>
> > This bug comes from a missing check when a function declaration has a
> > late-specified return type and a constrained auto type specifier. By
> > adding such a check, we can catch such uses and diagnose them as errors.
> >
> > Successfully bootstrapped and regretested on x86_64-pc-linux-gnu:
> > adds 6 new test results and 4 UNSUPPORTED results to g++.sum. The 4
> > UNSUPPORTED results are due to the fact that concepts are not supported
> > before c++20, so tests cannot pass with c++17 and lower standards.
> >
> > PR c++/100589
> >
> > gcc/cp/ChangeLog:
> >
> > * decl.cc (grokdeclarator): Issue an error for a declarator with
> > constrained auto type specifier and trailing return types.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/other/pr100589.C: New test.
>
> Thanks for the patch! Looks good to me overall, some minor comments
> below.
>
Thank you for the review! I'll make changes to the patch based on your
advice.
> >
> > Signed-off-by: Da Xie <xxie...@163.com>
> > ---
> > gcc/cp/decl.cc | 7 +++++++
> > gcc/testsuite/g++.dg/other/pr100589.C | 7 +++++++
> > 2 files changed, 14 insertions(+)
> > create mode 100644 gcc/testsuite/g++.dg/other/pr100589.C
> >
> > diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> > index 9ca8c6c4481..f283ed996a2 100644
> > --- a/gcc/cp/decl.cc
> > +++ b/gcc/cp/decl.cc
> > @@ -14037,6 +14037,13 @@ grokdeclarator (const cp_declarator *declarator,
> > "invalid use of %<decltype(auto)%>");
> > return error_mark_node;
> > }
> > + else if (is_constrained_auto (type))
> > + {
> > + error_at (typespec_loc, "invalid use of "
> > + "constrained auto type specifier "
> > + "in function with trailing return type");
>
> We should quote the 'auto' in this diagnostic by writing %<auto%>
> for consistency with the other diagnostics.
>
I have added an if statement to handle cases where the declarator
represents a named function. In such scenarios, an error will be issued,
including the function name, the use of constrained %<auto%>, and the
existence of a trailing return type. For all other cases, an error
message will indicate the invalid use of constrained %<auto%>.
Curiously, I found that if the same error message occurred multiple
times(In my case, the above error message does not print function names,
so every function/type declartions issues the same error message),
a single dg-error will catch all of them, even if these messages
are issued on different lines of code. I think this is the bug mentioned
in GCC Wiki (https://gcc.gnu.org/wiki/HowToPrepareATestcase#TODO).
Thankfully, in the updated testcase, the error messages are issued for a
function declaration and type declaration each. I have updated the
dg-error regex pattern to capture error messages separately for
functions and types. This ensures more precise matching and handling of
the respective error cases.
> > + return error_mark_node;
> > + }
> > tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node);
> > if (!tmpl)
> > if (tree late_auto = type_uses_auto (late_return_type))
> > diff --git a/gcc/testsuite/g++.dg/other/pr100589.C
> > b/gcc/testsuite/g++.dg/other/pr100589.C
> > new file mode 100644
> > index 00000000000..3fa054ed34d
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/other/pr100589.C
>
> Since this is a concepts-specific test let's name it
>
> g++.dg/cpp2a/concepts-pr100589.C
>
Renamed.
> > @@ -0,0 +1,7 @@
> > +// PR c++/100589
> > +// { dg-do compile { target c++20 } }
> > +
> > +template<class T>
> > +concept false_concept = false;
> > +
> > +false_concept auto f() -> int; // { dg-error "constrained auto type
> > specifier.* trailing return type" }
>
> It'd be good to also test a bare function type:
>
> using type = false_concept auto() -> int;
>
Test added.
> > \ No newline at end of file
> > --
> > 2.34.1
> >
> >
Thanks again for your reply. I will send updated patch when the
bootstrap and regression tests are finished.
