On 12/10/21 17:29, Marek Polacek wrote:
My r11-2202 was trying to enforce [dcl.type.auto.deduct]/4, which says "If the placeholder-type-specifier is of the form type-constraint[opt] decltype(auto), T shall be the placeholder alone." But this made us reject 'constexpr decltype(auto)', which, after clarification from CWG, should be valid. [dcl.type.auto.deduct]/4 is supposed to be a syntactic constraint, not semantic, so it's OK that the constexpr marks the object as const.As a consequence, checking TYPE_QUALS in do_auto_deduction is too late, and we have a FIXME there anyway. So in this patch I'm attempting to detect 'const decltype(auto)' earlier. If I'm going to use TYPE_QUALS, it needs to happen before we mark the object as const due to constexpr, that is, before grokdeclarator's /* A `constexpr' specifier used in an object declaration declares the object as `const'. */ if (constexpr_p && innermost_code != cdk_function) ... Constrained decltype(auto) was a little problem, hence the TYPENAME check. But in a typename context you can't use decltype(auto) anyway, I think.
I wonder about checking even earlier, like in cp_parser_decl_specifier_seq?
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/11? PR c++/102229 gcc/cp/ChangeLog: * decl.c (check_decltype_auto): New. (grokdeclarator): Call it. * pt.c (do_auto_deduction): Don't check decltype(auto) here. gcc/testsuite/ChangeLog: * g++.dg/cpp1y/decltype-auto5.C: New test. --- gcc/cp/decl.c | 58 ++++++++++++++------- gcc/cp/pt.c | 13 ----- gcc/testsuite/g++.dg/cpp1y/decltype-auto5.C | 35 +++++++++++++ 3 files changed, 74 insertions(+), 32 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp1y/decltype-auto5.C diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c index 56f80775ca0..196eac287eb 100644 --- a/gcc/cp/decl.c +++ b/gcc/cp/decl.c @@ -11354,6 +11354,33 @@ name_unnamed_type (tree type, tree decl) gcc_assert (!TYPE_UNNAMED_P (type)); }+/* Check that decltype(auto) was well-formed: only plain decltype(auto)+ is allowed. TYPE might contain a decltype(auto). Returns true if + there was a problem, false otherwise. */ + +static bool +check_decltype_auto (location_t loc, tree type) +{ + if (tree a = type_uses_auto (type)) + { + if (AUTO_IS_DECLTYPE (a)) + { + if (a != type) + { + error_at (loc, "%qT as type rather than plain " + "%<decltype(auto)%>", type); + return true; + } + else if (TYPE_QUALS (type) != TYPE_UNQUALIFIED) + { + error_at (loc, "%<decltype(auto)%> cannot be cv-qualified"); + return true; + } + } + } + return false; +} + /* Given declspecs and a declarator (abstract or otherwise), determine the name and type of the object declared and construct a DECL node for it. @@ -12702,25 +12729,9 @@ grokdeclarator (const cp_declarator *declarator, "allowed"); return error_mark_node; } - /* Only plain decltype(auto) is allowed. */ - if (tree a = type_uses_auto (type)) - { - if (AUTO_IS_DECLTYPE (a)) - { - if (a != type) - { - error_at (typespec_loc, "%qT as type rather than " - "plain %<decltype(auto)%>", type); - return error_mark_node; - } - else if (TYPE_QUALS (type) != TYPE_UNQUALIFIED) - { - error_at (typespec_loc, "%<decltype(auto)%> cannot be " - "cv-qualified"); - return error_mark_node; - } - } - } + + if (check_decltype_auto (typespec_loc, type)) + return error_mark_node;if (ctype == NULL_TREE&& decl_context == FIELD @@ -13080,6 +13091,15 @@ grokdeclarator (const cp_declarator *declarator,id_loc = declarator ? declarator->id_loc : input_location; + if (innermost_code != cdk_function+ /* Don't check this if it can be the artifical decltype(auto) + we created when building a constraint in a compound-requirement: + that the type-constraint is plain is going to be checked in + cp_parser_compound_requirement. */ + && decl_context != TYPENAME + && check_decltype_auto (id_loc, type)) + return error_mark_node; + /* A `constexpr' specifier used in an object declaration declares the object as `const'. */ if (constexpr_p && innermost_code != cdk_function) diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index 9834baf34db..6d5da17b9d0 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -29912,19 +29912,6 @@ do_auto_deduction (tree type, tree init, tree auto_node, return error_mark_node; targs = make_tree_vec (1); TREE_VEC_ELT (targs, 0) = deduced; - /* FIXME: These errors ought to be diagnosed at parse time. */ - if (type != auto_node) - { - if (complain & tf_error) - error ("%qT as type rather than plain %<decltype(auto)%>", type); - return error_mark_node; - } - else if (TYPE_QUALS (type) != TYPE_UNQUALIFIED) - { - if (complain & tf_error) - error ("%<decltype(auto)%> cannot be cv-qualified"); - return error_mark_node; - } } else { diff --git a/gcc/testsuite/g++.dg/cpp1y/decltype-auto5.C b/gcc/testsuite/g++.dg/cpp1y/decltype-auto5.C new file mode 100644 index 00000000000..01cc54fb71d --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/decltype-auto5.C @@ -0,0 +1,35 @@ +// PR c++/102229 +// { dg-do compile { target c++14 } } + +struct S { + constexpr static decltype(auto) x = 42; + const constexpr static decltype(auto) y = 42; // { dg-error "cannot be cv-qualified" } + + constexpr decltype(auto) mfn1 () { return 0; } + const constexpr decltype(auto) mfn2 () { return 0; } // { dg-error "cannot be cv-qualified" } +}; + +constexpr decltype(auto) i = 42; +const constexpr decltype(auto) j = 42; // { dg-error "cannot be cv-qualified" } + +constexpr decltype(auto) fn() { return 42; } +const decltype(auto) fn2() { return 42; } // { dg-error "cannot be cv-qualified" } + +auto constexpr foo() -> const decltype(auto) // { dg-error "cannot be cv-qualified" } +{ + return 0; +} + +#if __cpp_concepts +template<typename> +concept C = true; + +constexpr C decltype(auto) x1 = 0; +const constexpr C decltype(auto) x2 = 0; // { dg-error "cannot be cv-qualified" "" { target c++20 } } + +constexpr C decltype(auto) fn3() { return 0; } +const constexpr C decltype(auto) fn4() { return 0; } // { dg-error "cannot be cv-qualified" "" { target c++20 } } +#endif + +template<const decltype(auto) = 42> // { dg-error "cannot be cv-qualified" } +void g (); base-commit: 1e2eee7b29ed2afbc7edea6f3da7e6c8f70b1a4e
