I am friendly pinging the patch below ...
Dodji Seketeli <do...@redhat.com> a écrit:
> Hello,
>
> Consider this invalid example given in the PR, where T is not defined:
>
> 1 template<typename>
> 2 struct X {
> 3 using type = T;
> 4 };
>
> g++ yields the confusing diagnostics:
>
> test.cc:3:10: error: expected nested-name-specifier before 'type'
> using type = T;
> ^
> test.cc:3:10: error: using-declaration for non-member at class scope
> test.cc:3:15: error: expected ';' before '=' token
> using type = T;
> ^
> test.cc:3:15: error: expected unqualified-id before '=' token
>
> I think this is because in cp_parser_member_declaration we tentatively
> parse an alias declaration; we then have a somewhat meaningful
> diagnostic which alas is not emitted because we are parsing
> tentatively. As the parsing didn't succeed (because the input is
> invalid) we try to parse a using declaration, which fails as well; but
> then the diagnostic emitted is the one for the failed attempt at
> parsing a using declaration, not an alias declaration. Oops.
>
> The idea of this patch is to detect in advance that we want to parse
> an alias declaration, parse it non-tentatively, and then if an error
> arises, emit it.
>
> I also changed cp_parser_alias_declaration to get out directly when it
> detects that the type-id is invalid, rather than going on nonetheless
> and emitting more (irrelevant) error diagnostics.
>
> We are now getting the following output:
>
> test.cc:3:18: erreur: expected type-specifier before ‘T’
> using type = T;
> ^
> test.cc:3:18: erreur: ‘T’ does not name a type
>
> I don't really like the "before 'T'" there, but I think we maybe could
> revisit the format of what cp_parser_error emits in general, now that
> we have caret diagnostics; We could maybe do away with the "before T"
> altogether?
>
> In the mean time, it seems to me that this patch brings an improvement
> over what we already have in trunk, and the issue above could be
> addressed separately.
>
> Tested on x86_64-unknown-linux-gnu against trunk.
>
> gcc/cp/
>
> * parser.c (cp_parser_expecting_alias_declaration_p): New static
> function.
> (cp_parser_block_declaration): Use it.
> (cp_parser_member_declaration): Likewise. Don't parse the using
> declaration tentatively.
> (cp_parser_alias_declaration): Get out if the type-id is invalid.
>
> gcc/testsuite/
>
> * g++.dg/cpp0x/alias-decl-23.C: New test.
> ---
> gcc/cp/parser.c | 38
> +++++++++++++++++++++++-------
> gcc/testsuite/g++.dg/cpp0x/alias-decl-23.C | 7 ++++++
> 2 files changed, 36 insertions(+), 9 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/alias-decl-23.C
>
> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
> index e8c0378..cab2d09 100644
> --- a/gcc/cp/parser.c
> +++ b/gcc/cp/parser.c
> @@ -1937,6 +1937,8 @@ static bool cp_parser_using_declaration
> (cp_parser *, bool);
> static void cp_parser_using_directive
> (cp_parser *);
> +static bool cp_parser_expecting_alias_declaration_p
> + (cp_parser*);
> static tree cp_parser_alias_declaration
> (cp_parser *);
> static void cp_parser_asm_definition
> @@ -10292,11 +10294,7 @@ cp_parser_block_declaration (cp_parser *parser,
> cp_parser_using_directive (parser);
> /* If the second token after 'using' is '=', then we have an
> alias-declaration. */
> - else if (cxx_dialect >= cxx0x
> - && token2->type == CPP_NAME
> - && ((cp_lexer_peek_nth_token (parser->lexer, 3)->type == CPP_EQ)
> - || (cp_lexer_peek_nth_token (parser->lexer, 3)->keyword
> - == RID_ATTRIBUTE)))
> + else if (cp_parser_expecting_alias_declaration_p (parser))
> cp_parser_alias_declaration (parser);
> /* Otherwise, it's a using-declaration. */
> else
> @@ -15079,6 +15077,24 @@ cp_parser_using_declaration (cp_parser* parser,
> return true;
> }
>
> +/* Return TRUE if the coming tokens reasonably denote the beginning of
> + an alias declaration. */
> +
> +static bool
> +cp_parser_expecting_alias_declaration_p (cp_parser* parser)
> +{
> + if (cxx_dialect < cxx0x)
> + return false;
> + cp_parser_parse_tentatively (parser);
> + cp_parser_require_keyword (parser, RID_USING, RT_USING);
> + cp_parser_identifier (parser);
> + cp_parser_attributes_opt (parser);
> + cp_parser_require (parser, CPP_EQ, RT_EQ);
> + bool is_ok = !cp_parser_error_occurred (parser);
> + cp_parser_abort_tentative_parse (parser);
> + return is_ok;
> +}
> +
> /* Parse an alias-declaration.
>
> alias-declaration:
> @@ -15141,6 +15157,9 @@ cp_parser_alias_declaration (cp_parser* parser)
> if (parser->num_template_parameter_lists)
> parser->type_definition_forbidden_message = saved_message;
>
> + if (type == error_mark_node)
> + return error_mark_node;
> +
> cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
>
> if (cp_parser_error_occurred (parser))
> @@ -18849,10 +18868,11 @@ cp_parser_member_declaration (cp_parser* parser)
> else
> {
> tree decl;
> - cp_parser_parse_tentatively (parser);
> - decl = cp_parser_alias_declaration (parser);
> - if (cp_parser_parse_definitely (parser))
> - finish_member_declaration (decl);
> + if (cp_parser_expecting_alias_declaration_p (parser))
> + {
> + decl = cp_parser_alias_declaration (parser);
> + finish_member_declaration (decl);
> + }
> else
> cp_parser_using_declaration (parser,
> /*access_declaration_p=*/false);
> diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-23.C
> b/gcc/testsuite/g++.dg/cpp0x/alias-decl-23.C
> new file mode 100644
> index 0000000..086b5e5
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-23.C
> @@ -0,0 +1,7 @@
> +// Origin: PR c++/54401
> +// { dg-do compile { target c++11 } }
> +
> +template<typename>
> +struct X {
> + using type = T; // { dg-error "expected type-specifier|does not name a
> type" }
> +};
> --
> 1.7.11.4
--
Dodji
