attribs: Allow optional second arg for attr deprecated [PR102049]

  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


base-commit: f6a05b23cc2e53c38e8321ddb5d2cbe40737e506
  

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
  

On Mon, Oct 11, 2021 at 11:19 AM Marek Polacek via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Any thoughts?

I think it's a good idea, but then again I can't approve it, so...
well, who can, then?

>
> 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.

Looking forward to the fix-it hint support being added!

> >
> > 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
>
  

On 10/11/21 9:17 AM, Marek Polacek via Gcc-patches wrote:
> Any thoughts?

I'm a little unsure.  Clang just uses the replacement string
as the text of the fix-it note as is, so it does nothing to
help programmers make sure the replacement is in sync with
what it's supposed to replace.  E.g., for this Clang output
is below:

__attribute__ ((deprecated ("foo is bad", "use bar instead")))
void foo (void);
void baz (void) { foo (); }

int bar;

<source>:2:19: warning: 'foo' is deprecated: foo is bad 
[-Wdeprecated-declarations]
void baz (void) { foo (); }
                   ^~~
                   use bar instead

Since bar is a variable it's hard to see how it might be used
instead of the function foo().  Fix-its, as I understand them,
are meant not just as a visual clue but also to let IDEs and
other tools automatically apply the fixes.  With buggy fix-its
this obviously wouldn't work.

I think the replacement would be useful if it had to reference
an existing symbol of the same kind, and if the compiler helped
enforce it.  Otherwise it seems like a recipe for bit rot and
for tings/tools not working well together.

Martin

> 
> 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
>
  

On Mon, Nov 01, 2021 at 05:15:03PM -0600, Martin Sebor wrote:
> On 10/11/21 9:17 AM, Marek Polacek via Gcc-patches wrote:
> > Any thoughts?
> 
> I'm a little unsure.  Clang just uses the replacement string
> as the text of the fix-it note as is, so it does nothing to
> help programmers make sure the replacement is in sync with
> what it's supposed to replace.  E.g., for this Clang output
> is below:
> 
> __attribute__ ((deprecated ("foo is bad", "use bar instead")))
> void foo (void);
> void baz (void) { foo (); }
> 
> int bar;
> 
> <source>:2:19: warning: 'foo' is deprecated: foo is bad
> [-Wdeprecated-declarations]
> void baz (void) { foo (); }
>                   ^~~
>                   use bar instead
> 
> Since bar is a variable it's hard to see how it might be used
> instead of the function foo().  Fix-its, as I understand them,
> are meant not just as a visual clue but also to let IDEs and
> other tools automatically apply the fixes.  With buggy fix-its
> this obviously wouldn't work.
> 
> I think the replacement would be useful if it had to reference
> an existing symbol of the same kind, and if the compiler helped
> enforce it.  Otherwise it seems like a recipe for bit rot and
> for tings/tools not working well together.

OK, I think I'm not going to pursue this further.  I'll close the
PR and reference my patch in it, should this come up again in the
future.

Thanks,

> > 
> > 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
> > 
> 

Marek