https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115231
--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Nathaniel Shead <nsh...@gcc.gnu.org>: https://gcc.gnu.org/g:ca287145f23ec3ea987fc2eacde3994096cc528e commit r15-2779-gca287145f23ec3ea987fc2eacde3994096cc528e Author: Nathaniel Shead <nathanielosh...@gmail.com> Date: Sat Jun 15 22:50:14 2024 +1000 c++/modules: Ensure deduction guides are always reachable [PR115231] Deduction guides are represented as 'normal' functions currently, and have no special handling in modules. However, this causes some issues; by [temp.deduct.guide] a deduction guide is not found by normal name lookup and instead all reachable deduction guides for a class template should be considered, but this does not happen currently. To solve this, this patch ensures that all deduction guides are considered exported to ensure that they are always visible to importers if they are reachable. Another alternative here would be to add a new kind of "all reachable" flag to name lookup, but that is complicated by some difficulties in handling GM entities; this may be a better way to go if more kinds of entities end up needing this handling, however. Another issue here is that because deduction guides are "unrelated" functions, they will usually get discarded from the GMF, so this patch ensures that when finding dependencies, GMF deduction guides will also have bindings created. We do this in find_dependencies so that we don't unnecessarily create bindings for GMF deduction guides that are never reached; for consistency we do this for *all* deduction guides, not just GM ones. We also make sure that the opposite (a deduction guide being the only purview reference to a GMF template) correctly marks it as reachable. Finally, when merging deduction guides from multiple modules, the name lookup code may now return two-dimensional overload sets, so update callers to match. As a small drive-by improvement this patch also updates the error pretty printing code to add a space before the '->' when printing a deduction guide, so we get 'S(int) -> S<int>' instead of 'S(int)-> S<int>'. PR c++/115231 gcc/cp/ChangeLog: * error.cc (dump_function_decl): Add a space before '->' when printing deduction guides. * module.cc (depset::hash::add_binding_entity): Don't create bindings for guides here, only mark dependencies. (depset::hash::add_deduction_guides): New. (depset::hash::find_dependencies): Add deduction guide dependencies for a class template. (module_state::write_cluster): Always consider deduction guides as exported. * pt.cc (deduction_guides_for): Use 'lkp_iterator' instead of 'ovl_iterator'. gcc/testsuite/ChangeLog: * g++.dg/modules/dguide-1_a.C: New test. * g++.dg/modules/dguide-1_b.C: New test. * g++.dg/modules/dguide-2_a.C: New test. * g++.dg/modules/dguide-2_b.C: New test. * g++.dg/modules/dguide-3_a.C: New test. * g++.dg/modules/dguide-3_b.C: New test. * g++.dg/modules/dguide-3_c.C: New test. * g++.dg/modules/dguide-3_d.C: New test. Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
