On Wed, 2 Jun 2021, Jason Merrill wrote: > On 6/2/21 4:56 PM, Patrick Palka wrote: > > On Wed, 2 Jun 2021, Patrick Palka wrote: > > > > > On Wed, 2 Jun 2021, Jason Merrill wrote: > > > > > > > On 6/2/21 2:39 PM, Patrick Palka wrote: > > > > > Here, the dependent template name in the return type of f() resolves > > > > > to > > > > > an alias of int& after substitution, and we end up complaining about > > > > > qualifying this reference type with 'const' from > > > > > cp_build_qualified_type > > > > > rather than just silently dropping the qualification as per > > > > > [dcl.ref]/1. > > > > > > > > Hmm, the patch looks fine, but why does the TYPE_DECL test fail for the > > > > alias? > > > > > > Ah, I hadn't considered investigating that. It seems make_typename_type > > > always returns a _TYPE instead of a TYPE_DECL when resolving a dependent > > > name that's a template-id, regardless of the tf_keep_type_decl flag. > > > This can be easily fixed like so, and this change alone is sufficient to > > > fix the PR (no changes to qualttp20.C needed). Note that this change > > > should only have an effect when tf_keep_type_decl is passed to > > > make_typename_type, and the only such caller is the TYPENAME_TYPE case > > > of tsubst in question, so this change seems pretty safe. > > > > > > The downside is that we don't get the __restrict__-dropping > > > "improvement" as exhibited by qualttp20.C that the original patch > > > provides, so this other approach is more conservative in that sense. > > > > > > So shall we go with the original patch, or something like the following? > > > (If we go with the original patch, it just occurred to me that we could > > > remove tf_keep_type_decl altogether.) Testing in progress. > > > > For sake of concreteness, here's the full alternative patch for > > consideration (modulo ChangeLog): > > This seems better. I think the only non-type return from > lookup_template_class is error_mark_node; does it work to check that > specifically rather than !TYPE_P?
Indeed, checking for error_mark_node instead works nicely. Does the following look OK? Bootstrapped and regtested on x86_64-pc-linux-gnu. -- >8 -- Subject: [PATCH] c++: cv-qualified dependent name of alias tmpl [PR100592] Here, the dependent template name in the return type of f() resolves to an alias of int& after substitution, and we end up complaining about qualifying this reference type with 'const' from cp_build_qualified_type rather than just silently dropping the qualification as per [dcl.ref]/1. The problem is ultimately that make_typename_type ignores the tf_keep_type_decl flag when the dependent name is a template-id. This in turn causes the TYPE_DECL check within tsubst <case TYPENAME_TYPE> to fail, and so we end up not passing tf_ignore_bad_quals to cp_build_qualified_type. This patch fixes this by making make_typename_type respect the tf_keep_type_decl flag even in the case of a dependent template-id name. Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for trunk? PR c++/100592 gcc/cp/ChangeLog: * decl.c (make_typename_type): After dispatching to lookup_template_class, adjust the result to its TYPE_NAME and then consider the tf_keep_type_decl flag. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/alias-decl-71.C: New test. * g++.dg/template/qualttp20.C: Remove dg-error and augment. --- gcc/cp/decl.c | 13 +++++++++---- gcc/testsuite/g++.dg/cpp0x/alias-decl-71.C | 13 +++++++++++++ 2 files changed, 22 insertions(+), 4 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp0x/alias-decl-71.C diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c index fb21a3a1ae8..a3687dbb0dd 100644 --- a/gcc/cp/decl.c +++ b/gcc/cp/decl.c @@ -4136,10 +4136,15 @@ make_typename_type (tree context, tree name, enum tag_types tag_type, return error_mark_node; if (want_template) - return lookup_template_class (t, TREE_OPERAND (fullname, 1), - NULL_TREE, context, - /*entering_scope=*/0, - complain | tf_user); + { + t = lookup_template_class (t, TREE_OPERAND (fullname, 1), + NULL_TREE, context, + /*entering_scope=*/0, + complain | tf_user); + if (t == error_mark_node) + return error_mark_node; + t = TYPE_NAME (t); + } if (DECL_ARTIFICIAL (t) || !(complain & tf_keep_type_decl)) t = TREE_TYPE (t); diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-71.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-71.C new file mode 100644 index 00000000000..6a61f93a0b0 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-71.C @@ -0,0 +1,13 @@ +// PR c++/100592 +// { dg-do compile { target c++11 } } + +template<bool> +struct meta { + template<class> using if_c = int&; +}; + +template<bool B> +typename meta<B>::template if_c<void> const f(); + +using type = decltype(f<true>()); +using type = int&; -- 2.32.0.rc2