On Sun, 2 Mar 2025, xxie-xd wrote:
> * 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 believe that's actually because of the .* in your pattern, which also
matches trailing newlines and so it can greedily match errors issued
later in the testcase. Normally dg-error matches only errors occurring on
the line it's written in.
So for that reason it's better to use \[^\n\r\]* instead of .* as the
"match anything" pattern in a dg-error. Very rarely do we actually want
a dg-error to look into multiple lines of errors. This could use
documenting on the wiki page.
> 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.
>
>
