Any thoughts?
On Thu, Sep 23, 2021 at 12:16:36PM -0400, Marek Polacek via Gcc-patches wrote:
> Clang implements something we don't have:
>
> __attribute__((deprecated("message", "replacement")));
>
> which seems pretty neat so I wrote this patch to add it to gcc.
>
> It doesn't allow the optional second argument in the standard [[]]
> form so as not to clash with possible future standard additions.
>
> I had hoped we could print a nice fix-it replacement hint, but that
> won't be possible until warn_deprecated_use gets something better than
> input_location.
>
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>
> PR c++/102049
>
> gcc/c-family/ChangeLog:
>
> * c-attribs.c (c_common_attribute_table): Increase max_len for
> deprecated.
> (handle_deprecated_attribute): Allow an optional second argument
> in the GNU form of attribute deprecated.
>
> gcc/c/ChangeLog:
>
> * c-parser.c (c_parser_std_attribute): Give a diagnostic when
> the standard form of an attribute deprecated has a second argument.
>
> gcc/ChangeLog:
>
> * doc/extend.texi: Document attribute deprecated with an
> optional second argument.
> * tree.c (warn_deprecated_use): Print the replacement argument,
> if any.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/c2x-attr-deprecated-3.c: Adjust dg-error.
> * c-c++-common/Wdeprecated-arg-1.c: New test.
> ---
> gcc/c-family/c-attribs.c | 17 ++++++++++++-
> gcc/c/c-parser.c | 8 ++++++
> gcc/doc/extend.texi | 24 ++++++++++++++++++
> .../c-c++-common/Wdeprecated-arg-1.c | 21 ++++++++++++++++
> gcc/testsuite/gcc.dg/c2x-attr-deprecated-3.c | 2 +-
> gcc/tree.c | 25 +++++++++++++++----
> 6 files changed, 90 insertions(+), 7 deletions(-)
> create mode 100644 gcc/testsuite/c-c++-common/Wdeprecated-arg-1.c
>
> diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
> index 007b928c54b..ef857a9ae2c 100644
> --- a/gcc/c-family/c-attribs.c
> +++ b/gcc/c-family/c-attribs.c
> @@ -409,7 +409,7 @@ const struct attribute_spec c_common_attribute_table[] =
> to prevent its usage in source code. */
> { "no vops", 0, 0, true, false, false, false,
> handle_novops_attribute, NULL },
> - { "deprecated", 0, 1, false, false, false, false,
> + { "deprecated", 0, 2, false, false, false, false,
> handle_deprecated_attribute, NULL },
> { "unavailable", 0, 1, false, false, false, false,
> handle_unavailable_attribute, NULL },
> @@ -4107,6 +4107,21 @@ handle_deprecated_attribute (tree *node, tree name,
> error ("deprecated message is not a string");
> *no_add_attrs = true;
> }
> + else if (TREE_CHAIN (args) != NULL_TREE)
> + {
> + /* We allow an optional second argument in the GNU form of
> + attribute deprecated, which specifies the replacement. */
> + if (flags & ATTR_FLAG_CXX11)
> + {
> + error ("replacement argument only allowed in GNU attributes");
> + *no_add_attrs = true;
> + }
> + else if (TREE_CODE (TREE_VALUE (TREE_CHAIN (args))) != STRING_CST)
> + {
> + error ("replacement argument is not a string");
> + *no_add_attrs = true;
> + }
> + }
>
> if (DECL_P (*node))
> {
> diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
> index fa29d2c15fc..2b47f01d166 100644
> --- a/gcc/c/c-parser.c
> +++ b/gcc/c/c-parser.c
> @@ -4952,6 +4952,14 @@ c_parser_std_attribute (c_parser *parser, bool for_tm)
> TREE_VALUE (attribute)
> = c_parser_attribute_arguments (parser, takes_identifier,
> require_string, false);
> + if (c_parser_next_token_is (parser, CPP_COMMA)
> + && strcmp (IDENTIFIER_POINTER (name), "deprecated") == 0)
> + {
> + error_at (open_loc, "replacement argument only allowed in "
> + "GNU attributes");
> + c_parser_skip_until_found (parser, CPP_CLOSE_PAREN, NULL);
> + return error_mark_node;
> + }
> }
> else
> c_parser_balanced_token_sequence (parser);
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index 9501a60f20e..7d399f4b2bc 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -2860,6 +2860,7 @@ StrongAlias (allocate, alloc);
>
> @item deprecated
> @itemx deprecated (@var{msg})
> +@itemx deprecated (@var{msg}, @var{replacement})
> @cindex @code{deprecated} function attribute
> The @code{deprecated} attribute results in a warning if the function
> is used anywhere in the source file. This is useful when identifying
> @@ -2880,6 +2881,13 @@ results in a warning on line 3 but not line 2. The
> optional @var{msg}
> argument, which must be a string, is printed in the warning if
> present.
>
> +This attribute accepts an optional second argument which specifies
> +the replacement that ought to be used instead:
> +
> +@smallexample
> +int old_fn () __attribute__ ((deprecated("unsafe", "new_fn")));
> +@end smallexample
> +
> The @code{deprecated} attribute can also be used for variables and
> types (@pxref{Variable Attributes}, @pxref{Type Attributes}.)
>
> @@ -7409,6 +7417,7 @@ attribute is also not copied. @xref{Common Function
> Attributes}.
>
> @item deprecated
> @itemx deprecated (@var{msg})
> +@itemx deprecated (@var{msg}, @var{replacement})
> @cindex @code{deprecated} variable attribute
> The @code{deprecated} attribute results in a warning if the variable
> is used anywhere in the source file. This is useful when identifying
> @@ -7429,6 +7438,13 @@ results in a warning on line 3 but not line 2. The
> optional @var{msg}
> argument, which must be a string, is printed in the warning if
> present.
>
> +This attribute accepts an optional second argument which specifies
> +the replacement that ought to be used instead:
> +
> +@smallexample
> +extern int old_var __attribute__ ((deprecated("unsafe", "new_var")));
> +@end smallexample
> +
> The @code{deprecated} attribute can also be used for functions and
> types (@pxref{Common Function Attributes},
> @pxref{Common Type Attributes}).
> @@ -8492,6 +8508,7 @@ struct __attribute__ ((copy ( (struct A *)0)) B @{ /*
> @r{@dots{}} */ @};
>
> @item deprecated
> @itemx deprecated (@var{msg})
> +@itemx deprecated (@var{msg}, @var{replacement})
> @cindex @code{deprecated} type attribute
> The @code{deprecated} attribute results in a warning if the type
> is used anywhere in the source file. This is useful when identifying
> @@ -8522,6 +8539,13 @@ present. Control characters in the string will be
> replaced with
> escape sequences, and if the @option{-fmessage-length} option is set
> to 0 (its default value) then any newline characters will be ignored.
>
> +This attribute accepts an optional second argument which specifies
> +the replacement that ought to be used instead:
> +
> +@smallexample
> +typedef int oldtype __attribute__ ((deprecated("unsafe", "newtype")));
> +@end smallexample
> +
> The @code{deprecated} attribute can also be used for functions and
> variables (@pxref{Function Attributes}, @pxref{Variable Attributes}.)
>
> diff --git a/gcc/testsuite/c-c++-common/Wdeprecated-arg-1.c
> b/gcc/testsuite/c-c++-common/Wdeprecated-arg-1.c
> new file mode 100644
> index 00000000000..b03e0e42ad6
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/Wdeprecated-arg-1.c
> @@ -0,0 +1,21 @@
> +/* PR c++/102049 */
> +/* { dg-do compile } */
> +/* { dg-additional-options "-std=c++11" { target c++ } } */
> +
> +typedef int __attribute__((deprecated("obsolete", "newtype"))) oldtype;
> +__attribute__((deprecated("unsafe", "get_it_s"))) void get_it (int); /* {
> dg-message "declared here" } */
> +[[gnu::deprecated("g", "")]] void g(); /* { dg-error "only allowed in GNU
> attributes" } */
> +[[deprecated("h", "")]] void h(); /* { dg-error "only allowed in GNU
> attributes" } */
> +__attribute__((deprecated("unsafe", 1))) void f2(); /* { dg-error "argument
> is not a string" } */
> +__attribute__((deprecated("unsafe", "newvar"))) int oldvar; /* { dg-message
> "declared here" } */
> +
> +int
> +main ()
> +{
> + get_it (42); /* { dg-warning "is deprecated: unsafe" } */
> + /* { dg-message "use .get_it_s. instead" "" { target *-*-* } .-1 } */
> + oldtype t; /* { dg-warning "is deprecated: obsolete" } */
> + /* { dg-message "use .newtype. instead" "" { target *-*-* } .-1 } */
> + int i = oldvar; /* { dg-warning "is deprecated: unsafe" } */
> + /* { dg-message "use .newvar. instead" "" { target *-*-* } .-1 } */
> +}
> diff --git a/gcc/testsuite/gcc.dg/c2x-attr-deprecated-3.c
> b/gcc/testsuite/gcc.dg/c2x-attr-deprecated-3.c
> index 044725e5123..6cb70705bbf 100644
> --- a/gcc/testsuite/gcc.dg/c2x-attr-deprecated-3.c
> +++ b/gcc/testsuite/gcc.dg/c2x-attr-deprecated-3.c
> @@ -6,6 +6,6 @@
>
> [[deprecated(0)]] int b; /* { dg-error "expected" } */
>
> -[[deprecated("", 123)]] int c; /* { dg-error "expected" } */
> +[[deprecated("", 123)]] int c; /* { dg-error "only allowed in GNU
> attributes" } */
>
> [[deprecated((""))]] int d; /* { dg-error "expected" } */
> diff --git a/gcc/tree.c b/gcc/tree.c
> index 561b9cd56bd..5cb2d57a960 100644
> --- a/gcc/tree.c
> +++ b/gcc/tree.c
> @@ -12002,8 +12002,9 @@ bool
> warn_deprecated_use (tree node, tree attr)
> {
> escaped_string msg;
> + escaped_string rep;
>
> - if (node == 0 || !warn_deprecated_decl)
> + if (node == NULL_TREE || !warn_deprecated_decl)
> return false;
>
> if (!attr)
> @@ -12023,7 +12024,12 @@ warn_deprecated_use (tree node, tree attr)
> attr = lookup_attribute ("deprecated", attr);
>
> if (attr)
> - msg.escape (TREE_STRING_POINTER (TREE_VALUE (TREE_VALUE (attr))));
> + {
> + tree val = TREE_VALUE (attr);
> + msg.escape (TREE_STRING_POINTER (TREE_VALUE (val)));
> + if (TREE_CHAIN (val))
> + rep.escape (TREE_STRING_POINTER (TREE_VALUE (TREE_CHAIN (val))));
> + }
>
> bool w = false;
> if (DECL_P (node))
> @@ -12036,7 +12042,11 @@ warn_deprecated_use (tree node, tree attr)
> w = warning (OPT_Wdeprecated_declarations,
> "%qD is deprecated", node);
> if (w)
> - inform (DECL_SOURCE_LOCATION (node), "declared here");
> + {
> + if (rep)
> + inform (input_location, "use %qs instead", (const char *) rep);
> + inform (DECL_SOURCE_LOCATION (node), "declared here");
> + }
> }
> else if (TYPE_P (node))
> {
> @@ -12072,8 +12082,13 @@ warn_deprecated_use (tree node, tree attr)
> "type is deprecated");
> }
>
> - if (w && decl)
> - inform (DECL_SOURCE_LOCATION (decl), "declared here");
> + if (w)
> + {
> + if (rep)
> + inform (input_location, "use %qs instead", (const char *) rep);
> + if (decl)
> + inform (DECL_SOURCE_LOCATION (decl), "declared here");
> + }
> }
>
> return w;
>
> base-commit: f6a05b23cc2e53c38e8321ddb5d2cbe40737e506
> --
> 2.31.1
>
Marek
