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

Marek Polacek polacek@redhat.com
Tue Nov 2 20:35:58 GMT 2021


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



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