On Wed, 30 Mar 2022, Jason Merrill via Gcc-patches wrote:
> The recent change to reject __is_constructible for nested classes with DMI
> is breaking some code loudly that was previously only silently broken.
> Let's allow simple cases by immediately parsing DMI that do no name lookup;
> then being in complete class scope makes no difference.
Not sure if this is a problem in practice but it seems the initializer
processing step of cp_parser_late_parse_one_default_arg may involve name
lookup even if the parse itself didn't:
struct A {
struct B {
const A &a = {};
};
};
We used to accept this (very contrived example), but now reject with
error: invalid use of incomplete type ‘const struct A’
>
> Tested x86_64-pc-linux-gnu, applying to trunk.
>
> PR c++/96645
>
> gcc/cp/ChangeLog:
>
> * parser.cc (cp_parser_early_parsing_nsdmi): New.
> (cp_parser_member_declaration): Call it.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp0x/nsdmi10.C: Now OK.
> * g++.dg/ext/is_constructible3.C: Likewise.
> * g++.dg/ext/is_constructible7.C: Likewise.
> ---
> gcc/cp/parser.cc | 28 +++++++++++++++++++-
> gcc/testsuite/g++.dg/cpp0x/nsdmi10.C | 4 +--
> gcc/testsuite/g++.dg/ext/is_constructible3.C | 2 +-
> gcc/testsuite/g++.dg/ext/is_constructible7.C | 3 +--
> 4 files changed, 31 insertions(+), 6 deletions(-)
>
> diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> index 7e1c777364e..63c8af1c722 100644
> --- a/gcc/cp/parser.cc
> +++ b/gcc/cp/parser.cc
> @@ -2701,6 +2701,8 @@ static tree cp_parser_late_parse_one_default_arg
> (cp_parser *, tree, tree, tree);
> static void cp_parser_late_parsing_nsdmi
> (cp_parser *, tree);
> +static bool cp_parser_early_parsing_nsdmi
> + (cp_parser *, tree);
> static void cp_parser_late_parsing_default_args
> (cp_parser *, tree);
> static tree cp_parser_sizeof_operand
> @@ -27478,7 +27480,8 @@ cp_parser_member_declaration (cp_parser* parser)
> if (DECL_DECLARES_FUNCTION_P (decl))
> cp_parser_save_default_args (parser, STRIP_TEMPLATE (decl));
> else if (TREE_CODE (decl) == FIELD_DECL
> - && DECL_INITIAL (decl))
> + && DECL_INITIAL (decl)
> + && !cp_parser_early_parsing_nsdmi (parser, decl))
> /* Add DECL to the queue of NSDMI to be parsed later. */
> vec_safe_push (unparsed_nsdmis, decl);
> }
> @@ -32292,6 +32295,29 @@ cp_parser_late_parsing_nsdmi (cp_parser *parser,
> tree field)
> DECL_INITIAL (field) = def;
> }
>
> +/* If the DEFERRED_PARSE for FIELD is safe to parse immediately, do so.
> + Returns true if deferred parsing is no longer needed. */
> +
> +static bool
> +cp_parser_early_parsing_nsdmi (cp_parser *parser, tree field)
> +{
> + tree init = DECL_INITIAL (field);
> + if (TREE_CODE (init) != DEFERRED_PARSE)
> + return true;
> +
> + cp_token_cache *tokens = DEFPARSE_TOKENS (init);
> + for (cp_token *p = tokens->first; p != tokens->last; ++p)
> + if (p->type == CPP_NAME
> + || p->keyword == RID_THIS
> + || p->keyword == RID_OPERATOR)
> + /* There's a name to look up or 'this', give up. */
> + return false;
> +
> + /* It's trivial, parse now. */
> + cp_parser_late_parsing_nsdmi (parser, field);
> + return true;
> +}
> +
> /* FN is a FUNCTION_DECL which may contains a parameter with an
> unparsed DEFERRED_PARSE. Parse the default args now. This function
> assumes that the current scope is the scope in which the default
> diff --git a/gcc/testsuite/g++.dg/cpp0x/nsdmi10.C
> b/gcc/testsuite/g++.dg/cpp0x/nsdmi10.C
> index d8588b7f29e..a965f7bc333 100644
> --- a/gcc/testsuite/g++.dg/cpp0x/nsdmi10.C
> +++ b/gcc/testsuite/g++.dg/cpp0x/nsdmi10.C
> @@ -6,7 +6,7 @@ struct A1 {
> int y1 = 1;
> };
>
> - A1(const B1& opts = B1()) {} // { dg-error "default member initializer" }
> + A1(const B1& opts = B1()) {}
> };
>
> struct A2 {
> @@ -14,5 +14,5 @@ struct A2 {
> int x2, y2 = 1;
> };
>
> - A2(const B2& opts = B2()) {} // { dg-error "default member initializer" }
> + A2(const B2& opts = B2()) {}
> };
> diff --git a/gcc/testsuite/g++.dg/ext/is_constructible3.C
> b/gcc/testsuite/g++.dg/ext/is_constructible3.C
> index 305751d28e2..c7c58746cd0 100644
> --- a/gcc/testsuite/g++.dg/ext/is_constructible3.C
> +++ b/gcc/testsuite/g++.dg/ext/is_constructible3.C
> @@ -8,7 +8,7 @@ struct A {
> B() = default;
> };
>
> - static constexpr bool v = __is_constructible (B); // { dg-error "member
> initializer" }
> + static constexpr bool v = __is_constructible (B);
>
> };
>
> diff --git a/gcc/testsuite/g++.dg/ext/is_constructible7.C
> b/gcc/testsuite/g++.dg/ext/is_constructible7.C
> index 76a63bba5d0..013a1df03c6 100644
> --- a/gcc/testsuite/g++.dg/ext/is_constructible7.C
> +++ b/gcc/testsuite/g++.dg/ext/is_constructible7.C
> @@ -12,7 +12,7 @@ using true_type = bool_constant<true>;
>
> template<typename T>
> struct is_default_constructible
> - : bool_constant<__is_constructible(T)> // { dg-error "default member init"
> }
> + : bool_constant<__is_constructible(T)>
> { };
>
> void testVarStruct()
> @@ -22,7 +22,6 @@ void testVarStruct()
> int number = 5; // compiles, if remove initialization
> };
>
> - // { dg-prune-output "could not convert" }
> is_default_constructible<A>::type t = true_type{};
> };
> }
>
> base-commit: 150ab50f7449cf5b496bbe6e5c60cb1adb2e2d6c
> --
> 2.27.0
>
>
