[PATCH] c++: P2360R0: Extend init-stmt to allow alias-decl [PR102617]
Jason Merrill
jason@redhat.com
Thu Oct 21 20:56:57 GMT 2021
On 10/21/21 16:26, Marek Polacek wrote:
> The following patch implements C++23 P2360R0. This proposal merely
> extends init-statement to contain alias-declaration. init-statement
> is used in if/for/switch. The unsightly duplication of the new code
> seems to be necessary to handle
>
> for ( init-statement condition[opt] ; expression[opt] ) statement
>
> as well as
>
> for ( init-statement[opt] for-range-declaration : for-range-initializer ) statement
It seems like the duplication of the new code is a consequence of the
duplication of the old code. I'd think we could remove the duplication
by remembering the result of cp_parser_range_based_for_with_init_p and
then recursing at the end if it was true. Or check it in cp_parser_for
and call cp_parser_init_statement twice.
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>
> PR c++/102617
>
> gcc/cp/ChangeLog:
>
> * parser.c (cp_parser_init_statement): Allow alias-declaration in
> init-statement.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp23/init-stmt1.C: New test.
> * g++.dg/cpp23/init-stmt2.C: New test.
> ---
> gcc/cp/parser.c | 52 +++++++++++++++++++------
> gcc/testsuite/g++.dg/cpp23/init-stmt1.C | 31 +++++++++++++++
> gcc/testsuite/g++.dg/cpp23/init-stmt2.C | 25 ++++++++++++
> 3 files changed, 96 insertions(+), 12 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp23/init-stmt1.C
> create mode 100644 gcc/testsuite/g++.dg/cpp23/init-stmt2.C
>
> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
> index 49d951cfb19..8ba5370740e 100644
> --- a/gcc/cp/parser.c
> +++ b/gcc/cp/parser.c
> @@ -12040,6 +12040,7 @@ cp_parser_handle_directive_omp_attributes (cp_parser *parser, tree *pattrs,
> init-statement:
> expression-statement
> simple-declaration
> + alias-declaration
>
> TM Extension:
>
> @@ -13987,12 +13988,13 @@ cp_parser_iteration_statement (cp_parser* parser, bool *if_p, bool ivdep,
> return statement;
> }
>
> -/* Parse a init-statement or the declarator of a range-based-for.
> +/* Parse an init-statement or the declarator of a range-based-for.
> Returns true if a range-based-for declaration is seen.
>
> init-statement:
> expression-statement
> - simple-declaration */
> + simple-declaration
> + alias-declaration */
>
> static bool
> cp_parser_init_statement (cp_parser *parser, tree *decl)
> @@ -14013,11 +14015,24 @@ cp_parser_init_statement (cp_parser *parser, tree *decl)
> {
> tree dummy;
> cp_parser_parse_tentatively (parser);
> - /* Parse the declaration. */
> - cp_parser_simple_declaration (parser,
> - /*function_definition_allowed_p=*/false,
> - &dummy);
> - cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
> + if (cp_lexer_next_token_is_keyword (parser->lexer, RID_USING))
> + {
> + cp_parser_alias_declaration (parser);
> + if (cxx_dialect < cxx23
> + && !cp_parser_uncommitted_to_tentative_parse_p (parser))
> + pedwarn (cp_lexer_peek_token (parser->lexer)->location,
> + OPT_Wc__23_extensions,
> + "alias-declaration in init-statement only "
> + "available with %<-std=c++23%> or %<-std=gnu++23%>");
> + }
> + else
> + {
> + /* Parse the declaration. */
> + cp_parser_simple_declaration (parser,
> + /*function_definition_allowed_p=*/
> + false, &dummy);
> + cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
> + }
> if (!cp_parser_parse_definitely (parser))
> /* That didn't work, try to parse it as an expression-statement. */
> cp_parser_expression_statement (parser, NULL_TREE);
> @@ -14038,10 +14053,23 @@ cp_parser_init_statement (cp_parser *parser, tree *decl)
> /* We're going to speculatively look for a declaration, falling back
> to an expression, if necessary. */
> cp_parser_parse_tentatively (parser);
> - /* Parse the declaration. */
> - cp_parser_simple_declaration (parser,
> - /*function_definition_allowed_p=*/false,
> - decl);
> + bool expect_semicolon_p = true;
> + if (cp_lexer_next_token_is_keyword (parser->lexer, RID_USING))
> + {
> + cp_parser_alias_declaration (parser);
> + expect_semicolon_p = false;
> + if (cxx_dialect < cxx23
> + && !cp_parser_uncommitted_to_tentative_parse_p (parser))
> + pedwarn (cp_lexer_peek_token (parser->lexer)->location,
> + OPT_Wc__23_extensions,
> + "alias-declaration in init-statement only "
> + "available with %<-std=c++23%> or %<-std=gnu++23%>");
> + }
> + else
> + /* Parse the declaration. */
> + cp_parser_simple_declaration (parser,
> + /*function_definition_allowed_p=*/false,
> + decl);
> parser->colon_corrects_to_scope_p = saved_colon_corrects_to_scope_p;
> if (cp_lexer_next_token_is (parser->lexer, CPP_COLON))
> {
> @@ -14054,7 +14082,7 @@ cp_parser_init_statement (cp_parser *parser, tree *decl)
> "range-based %<for%> loops only available with "
> "%<-std=c++11%> or %<-std=gnu++11%>");
> }
> - else
> + else if (expect_semicolon_p)
> /* The ';' is not consumed yet because we told
> cp_parser_simple_declaration not to. */
> cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
> diff --git a/gcc/testsuite/g++.dg/cpp23/init-stmt1.C b/gcc/testsuite/g++.dg/cpp23/init-stmt1.C
> new file mode 100644
> index 00000000000..29e3256aae6
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp23/init-stmt1.C
> @@ -0,0 +1,31 @@
> +// PR c++/102617
> +// P2360R0: Extend init-statement to allow alias-declaration
> +// { dg-do compile { target c++20 } }
> +// Test valid use.
> +
> +int v[10];
> +
> +void
> +g ()
> +{
> + for (using T = int; (T) false;) // { dg-error "only available with" "" { target c++20_only } }
> + ;
> + for (using T = int; T e : v) // { dg-error "only available with" "" { target c++20_only } }
> + (void) e;
> + if (using T = int; true) // { dg-error "only available with" "" { target c++20_only } }
> + {
> + T x = 0;
> + (void) x;
> + }
> + if constexpr (using T = int; true) // { dg-error "only available with" "" { target c++20_only } }
> + {
> + T x = 0;
> + (void) x;
> + }
> + switch (using T = int; 42) // { dg-error "only available with" "" { target c++20_only } }
> + case 42:
> + {
> + T x = 0;
> + (void) x;
> + }
> +}
> diff --git a/gcc/testsuite/g++.dg/cpp23/init-stmt2.C b/gcc/testsuite/g++.dg/cpp23/init-stmt2.C
> new file mode 100644
> index 00000000000..ca6201bc340
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp23/init-stmt2.C
> @@ -0,0 +1,25 @@
> +// PR c++/102617
> +// P2360R0: Extend init-statement to allow alias-declaration
> +// { dg-do compile { target c++23 } }
> +// Test invalid use.
> +
> +int v[10];
> +namespace N { using X = int; }
> +
> +void
> +g ()
> +{
> + for (using N::X; false;) // { dg-error "expected" }
> + ;
> + for (using N::X; int e : v) // { dg-error "expected" }
> + (void) e;
> + for (using T = int; using U = int; int e : v) // { dg-error "" }
> + ;
> + if (using N::X; false) // { dg-error "expected" }
> + {}
> + switch (using N::X; 0) // { dg-error "expected" }
> + ;
> + if (using T = int;) // { dg-error "expected" }
> + {
> + }
> +}
>
> base-commit: 1373066a46d8d47abd97e46a005aef3b3dbfe94a
>
More information about the Gcc-patches
mailing list