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. > > 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. > + 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 > @@ -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; > \ No newline at end of file > -- > 2.34.1 > >