[PATCH] attribs: Implement -Wno-attributes=vendor::attr [PR101940]

[Marek Polacek <polacek@redhat.com>]

It is desirable for -Wattributes to warn about e.g.

[[deprecate]] void g(); // typo, should warn

However, -Wattributes also warns about vendor-specific attributes
(that's because lookup_scoped_attribute_spec -> find_attribute_namespace
finds nothing), which, with -Werror, causes grief.  We don't want the
-Wattributes warning for

[[company::attr]] void f();

GCC warns because it doesn't know the "company" namespace; it only knows
the "gnu" and "omp" namespaces.  We could entirely disable warning about
attributes in unknown scopes but then the compiler would also miss typos
like

  [[company::attrx]] void f();

or

  [[gmu::warn_used_result]] int write();

so that is not a viable solution.  A workaround is to use a #pragma:

  #pragma GCC diagnostic push
  #pragma GCC diagnostic ignored "-Wattributes"
  [[company::attr]] void f() {}
  #pragma GCC diagnostic pop

but that's a mouthful and awkward to use and could also hide typos.  In
fact, any macro-based solution doesn't seem like a way forward.

This patch implements -Wno-attributes=, which takes these arguments:

company::attr
company::
clang

The last one is a special option to ignore clang-only attributes; in
this patch it is accepted but currently has no effect.

This option should go well with using @file: the user could have a file
containing
-Wno-attributes=vendor::attr1,vendor::attr2
and then invoke gcc with '@attrs' or similar.

I've also added a new pragma which has the same effect:

The pragma along with the new option should help with various static
analysis tools.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

	PR c++/101940

gcc/ChangeLog:

	* attribs.c (struct scoped_attributes): Add a bool member.
	(lookup_scoped_attribute_spec): Forward declare.
	(register_scoped_attributes): New bool parameter, defaulted to
	false.  Use it.
	(handle_ignored_attributes_option): New function.
	(free_attr_data): New function.
	(init_attributes): Call handle_ignored_attributes_option.
	(attr_namespace_ignored_p): New function.
	(decl_attributes): Check attr_namespace_ignored_p before
	warning.
	* attribs.h (free_attr_data): Declare.
	(register_scoped_attributes): Adjust declaration.
	(handle_ignored_attributes_option): Declare.
	* common.opt (Wattributes=): New option with a variable.
	* doc/extend.texi: Document #pragma GCC diagnostic ignored_attributes.
	* doc/invoke.texi: Document -Wno-attributes=.
	* opts.c (common_handle_option) <case OPT_Wattributes_>: Handle.
	* plugin.h (register_scoped_attributes): Adjust declaration.

gcc/c-family/ChangeLog:

	* c-pragma.c (handle_pragma_diagnostic): Handle #pragma GCC diagnostic
	ignored_attributes.

gcc/c/ChangeLog:

	* c-decl.c (c_parse_final_cleanups): Call free_attr_data.

gcc/cp/ChangeLog:

	* decl2.c (c_parse_final_cleanups): Call free_attr_data.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wno-attributes-1.c: New test.
	* c-c++-common/Wno-attributes-2.c: New test.
---
 gcc/attribs.c                                 | 122 +++++++++++++++++-
 gcc/attribs.h                                 |   5 +-
 gcc/c-family/c-pragma.c                       |  22 +++-
 gcc/c/c-decl.c                                |   2 +
 gcc/common.opt                                |   9 +-
 gcc/cp/decl2.c                                |   2 +
 gcc/doc/extend.texi                           |  19 +++
 gcc/doc/invoke.texi                           |  18 +++
 gcc/opts.c                                    |  14 ++
 gcc/plugin.h                                  |   4 +-
 gcc/testsuite/c-c++-common/Wno-attributes-1.c |  40 ++++++
 gcc/testsuite/c-c++-common/Wno-attributes-2.c |  41 ++++++
 12 files changed, 289 insertions(+), 9 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-1.c
 create mode 100644 gcc/testsuite/c-c++-common/Wno-attributes-2.c

diff --git a/gcc/attribs.c b/gcc/attribs.c
index 83fafc98b7d..c85f3aedc4d 100644
--- a/gcc/attribs.c
+++ b/gcc/attribs.c
@@ -87,6 +87,8 @@ struct scoped_attributes
   const char *ns;
   vec<attribute_spec> attributes;
   hash_table<attribute_hasher> *attribute_hash;
+  /* True if we should not warn about unknown attributes in this NS.  */
+  bool ignored_p;
 };
 
 /* The table of scope attributes.  */
@@ -95,6 +97,8 @@ static vec<scoped_attributes> attributes_table;
 static scoped_attributes* find_attribute_namespace (const char*);
 static void register_scoped_attribute (const struct attribute_spec *,
 				       scoped_attributes *);
+static const struct attribute_spec *lookup_scoped_attribute_spec (const_tree,
+								  const_tree);
 
 static bool attributes_initialized = false;
 
@@ -121,12 +125,14 @@ extract_attribute_substring (struct substring *str)
 
 /* Insert an array of attributes ATTRIBUTES into a namespace.  This
    array must be NULL terminated.  NS is the name of attribute
-   namespace.  The function returns the namespace into which the
-   attributes have been registered.  */
+   namespace.  IGNORED_P is true iff all unknown attributes in this
+   namespace should be ignored for the purposes of -Wattributes.  The
+   function returns the namespace into which the attributes have been
+   registered.  */
 
 scoped_attributes *
 register_scoped_attributes (const struct attribute_spec *attributes,
-			    const char *ns)
+			    const char *ns, bool ignored_p /*=false*/)
 {
   scoped_attributes *result = NULL;
 
@@ -144,9 +150,12 @@ register_scoped_attributes (const struct attribute_spec *attributes,
       memset (&sa, 0, sizeof (sa));
       sa.ns = ns;
       sa.attributes.create (64);
+      sa.ignored_p = ignored_p;
       result = attributes_table.safe_push (sa);
       result->attribute_hash = new hash_table<attribute_hasher> (200);
     }
+  else
+    result->ignored_p |= ignored_p;
 
   /* Really add the attributes to their namespace now.  */
   for (unsigned i = 0; attributes[i].name != NULL; ++i)
@@ -224,6 +233,94 @@ check_attribute_tables (void)
 				 attribute_tables[j][l].name));
 }
 
+/* Used to stash pointers to allocated memory so that we can free them at
+   the end of parsing of all TUs. */
+static vec<attribute_spec *> ignored_attributes_table;
+
+/* Parse arguments ARGS of -Wno-attributes=.
+   Currently we accept:
+     vendor::attr
+     vendor::
+   and as a special case:
+     clang
+   This functions also registers the parsed attributes so that we don't
+   warn that we don't recognize them.  */
+
+void
+handle_ignored_attributes_option (vec<char *> *v)
+{
+  if (v == nullptr)
+    return;
+
+  for (auto opt : v)
+    {
+      if (strcmp (opt, "clang") == 0)
+	{
+	  // TODO
+	  continue;
+	}
+      char *q = strstr (opt, "::");
+      /* We don't accept '::attr'.  */
+      if (q == nullptr || q == opt)
+	{
+	  error ("wrong argument to ignored attributes");
+	  inform (input_location, "valid format is %<ns::attr%>, %<ns::%>, "
+		  "or %<clang%>");
+	  continue;
+	}
+      /* Cut off the vendor part.  */
+      *q = '\0';
+      const char *vendor = opt;
+      char *attr = q + 2;
+      /* Verify that they look valid.  */
+      auto valid_p = [](const char *s) {
+	for (; *s != '\0'; ++s)
+	  if (!ISALNUM (*s) && *s != '_')
+	    return false;
+	return true;
+      };
+      if (!valid_p (vendor) || !valid_p (attr))
+	{
+	  error ("wrong argument to ignored attributes");
+	  continue;
+	}
+      /* Turn "__attr__" into "attr" so that we have a canonical form of
+	 attribute names.  */
+      const size_t l = strlen (attr);
+      if (l > 4 && attr[0] == '_' && attr[1] == '_'
+	  && attr[l - 1] == '_' && attr[l - 2] == '_')
+	{
+	  attr[l - 2] = '\0';
+	  attr += 2;
+	}
+      /* If we've already seen this vendor::attr, ignore it.  Attempting to
+	 register it twice would lead to a crash.  */
+      if (lookup_scoped_attribute_spec (get_identifier (vendor),
+					get_identifier (attr)))
+	continue;
+      /* In the "vendor::" case, we should ignore *any* attribute coming
+	 from this attribute namespace.  */
+      const bool ignored_ns = attr[0] == '\0';
+      /* Create a table with extra attributes which we will register.
+	 We can't free it here, so squirrel away the pointers.  */
+      attribute_spec *table = new attribute_spec[2];
+      ignored_attributes_table.safe_push (table);
+      table[0] = { ignored_ns ? nullptr : attr, 0, 0, false, false,
+		   false, false, nullptr, nullptr };
+      table[1] = { nullptr, 0, 0, false, false, false, false, nullptr, nullptr };
+      register_scoped_attributes (table, vendor, ignored_ns);
+    }
+}
+
+/* Free data we might have allocated when adding extra attributes.  */
+
+void
+free_attr_data ()
+{
+  for (auto x : ignored_attributes_table)
+    delete[] x;
+}
+
 /* Initialize attribute tables, and make some sanity checks if checking is
    enabled.  */
 
@@ -252,6 +349,9 @@ init_attributes (void)
     /* Put all the GNU attributes into the "gnu" namespace.  */
     register_scoped_attributes (attribute_tables[i], "gnu");
 
+  vec<char *> *ignored = (vec<char *> *) flag_ignored_attributes;
+  handle_ignored_attributes_option (ignored);
+
   invoke_plugin_callbacks (PLUGIN_ATTRIBUTES, NULL);
   attributes_initialized = true;
 }
@@ -456,6 +556,19 @@ diag_attr_exclusions (tree last_decl, tree node, tree attrname,
   return found;
 }
 
+/* Return true iff we should not complain about unknown attributes
+   coming from the attribute namespace NS.  This is the case for
+   the -Wno-attributes=ns:: command-line option.  */
+
+static bool
+attr_namespace_ignored_p (tree ns)
+{
+  if (ns == NULL_TREE)
+    return false;
+  scoped_attributes *r = find_attribute_namespace (IDENTIFIER_POINTER (ns));
+  return r && r->ignored_p;
+}
+
 /* Process the attributes listed in ATTRIBUTES and install them in *NODE,
    which is either a DECL (including a TYPE_DECL) or a TYPE.  If a DECL,
    it should be modified in place; if a TYPE, a copy should be created
@@ -556,7 +669,8 @@ decl_attributes (tree *node, tree attributes, int flags,
 
       if (spec == NULL)
 	{
-	  if (!(flags & (int) ATTR_FLAG_BUILT_IN))
+	  if (!(flags & (int) ATTR_FLAG_BUILT_IN)
+	      && !attr_namespace_ignored_p (ns))
 	    {
 	      if (ns == NULL_TREE || !cxx11_attr_p)
 		warning (OPT_Wattributes, "%qE attribute directive ignored",
diff --git a/gcc/attribs.h b/gcc/attribs.h
index 138c509bce1..96a527f67a9 100644
--- a/gcc/attribs.h
+++ b/gcc/attribs.h
@@ -21,6 +21,7 @@ along with GCC; see the file COPYING3.  If not see
 #define GCC_ATTRIBS_H
 
 extern const struct attribute_spec *lookup_attribute_spec (const_tree);
+extern void free_attr_data ();
 extern void init_attributes (void);
 
 /* Process the attributes listed in ATTRIBUTES and install them in *NODE,
@@ -40,12 +41,14 @@ extern void apply_tm_attr (tree, tree);
 extern tree make_attribute (const char *, const char *, tree);
 
 extern struct scoped_attributes* register_scoped_attributes (const struct attribute_spec *,
-							     const char *);
+							     const char *,
+							     bool = false);
 
 extern char *sorted_attr_string (tree);
 extern bool common_function_versions (tree, tree);
 extern tree make_dispatcher_decl (const tree);
 extern bool is_function_default_version (const tree);
+extern void handle_ignored_attributes_option (vec<char *> *);
 
 /* Return a type like TTYPE except that its TYPE_ATTRIBUTES
    is ATTRIBUTE.
diff --git a/gcc/c-family/c-pragma.c b/gcc/c-family/c-pragma.c
index a9be8df0384..3f7b8380d93 100644
--- a/gcc/c-family/c-pragma.c
+++ b/gcc/c-family/c-pragma.c
@@ -764,7 +764,7 @@ handle_pragma_diagnostic(cpp_reader *ARG_UNUSED(dummy))
   if (token != CPP_NAME)
     {
       warning_at (loc, OPT_Wpragmas,
-		  "missing [error|warning|ignored|push|pop]"
+		  "missing [error|warning|ignored|push|pop|ignored_attributes]"
 		  " after %<#pragma GCC diagnostic%>");
       return;
     }
@@ -787,10 +787,28 @@ handle_pragma_diagnostic(cpp_reader *ARG_UNUSED(dummy))
       diagnostic_pop_diagnostics (global_dc, input_location);
       return;
     }
+  else if (strcmp (kind_string, "ignored_attributes") == 0)
+    {
+      token = pragma_lex (&x, &loc);
+      if (token != CPP_STRING)
+	{
+	  warning_at (loc, OPT_Wpragmas,
+		      "missing attribute name after %<#pragma GCC diagnostic "
+		      "ignored_attributes%>");
+	  return;
+	}
+      char *args = xstrdup (TREE_STRING_POINTER (x));
+      auto_vec<char *> v;
+      for (char *p = strtok (args, ","); p; p = strtok (NULL, ","))
+	v.safe_push (p);
+      handle_ignored_attributes_option (&v);
+      /* ??? We can't free (args); here.  */
+      return;
+    }
   else
     {
       warning_at (loc, OPT_Wpragmas,
-		  "expected [error|warning|ignored|push|pop]"
+		  "expected [error|warning|ignored|push|pop|ignored_attributes]"
 		  " after %<#pragma GCC diagnostic%>");
       return;
     }
diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index 771efa3eadf..345c8f9d620 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -12295,6 +12295,8 @@ c_parse_final_cleanups (void)
     c_write_global_declarations_1 (BLOCK_VARS (DECL_INITIAL (t)));
   c_write_global_declarations_1 (BLOCK_VARS (ext_block));
 
+  free_attr_data ();
+
   if (!in_lto_p)
     free_attr_access_data ();
 
diff --git a/gcc/common.opt b/gcc/common.opt
index b921f5e3b25..0da1d714819 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -80,7 +80,7 @@ int flag_gen_aux_info = 0
 Variable
 int flag_shlib
 
-; These two are really VEC(char_p,heap) *.
+; These three are really VEC(char_p,heap) *.
 
 Variable
 void *flag_instrument_functions_exclude_functions
@@ -88,6 +88,9 @@ void *flag_instrument_functions_exclude_functions
 Variable
 void *flag_instrument_functions_exclude_files
 
+Variable
+void *flag_ignored_attributes
+
 ; Generic structs (e.g. templates not explicitly specialized)
 ; may not have a compilation unit associated with them, and so
 ; may need to be treated differently from ordinary structs.
@@ -546,6 +549,10 @@ Wattributes
 Common Var(warn_attributes) Init(1) Warning
 Warn about inappropriate attribute usage.
 
+Wattributes=
+Common Joined
+Do not warn about specified attributes.
+
 Wattribute-alias
 Common Alias(Wattribute_alias=, 1, 0) Warning
 Warn about type safety and similar errors and mismatches in declarations with alias attributes.
diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
index a79a70ba9c2..58388c51dab 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -5305,6 +5305,8 @@ c_parse_final_cleanups (void)
   cp_tree_c_finish_parsing ();
   clear_consteval_vfns (consteval_vtables);
 
+  free_attr_data ();
+
   /* The entire file is now complete.  If requested, dump everything
      to a file.  */
   dump_tu ();
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 9501a60f20e..48eaf16d209 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -23745,6 +23745,25 @@ restored.
   foo(d);                       /* depends on command-line options */
 @end smallexample
 
+@item #pragma GCC diagnostic ignored_attributes
+
+Similarly to @option{-Wno-attributes=}, this pragma allows users to suppress
+warnings about unknown scoped attributes (in C++11 and C2X).  For example,
+@code{#pragma GCC diagnostic ignored_attributes "vendor::attr"} disables
+warning about the following declaration:
+
+@smallexample
+[[vendor::attr]] void f();
+@end smallexample
+
+whereas @code{#pragma GCC diagnostic ignored_attributes "vendor::"} prevents
+warning about both of these declarations:
+
+@smallexample
+[[vendor::safe]] void f();
+[[vendor::unsafe]] void f2();
+@end smallexample
+
 @end table
 
 GCC also offers a simple mechanism for printing messages during
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 4acb94181d2..7c7241cdb88 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -8621,6 +8621,24 @@ unrecognized attributes, function attributes applied to variables,
 etc.  This does not stop errors for incorrect use of supported
 attributes.
 
+Additionally, using @option{-Wno-attributes=}, it is possible to suppress
+warnings about unknown scoped attributes (in C++11 and C2X).  For example,
+@option{-Wno-attributes=vendor::attr} disables warning about the following
+declaration:
+
+@smallexample
+[[vendor::attr]] void f();
+@end smallexample
+
+It is also possible to disable warning about all attributes in a namespace
+using @option{-Wno-attributes=vendor::} which prevents warning about both
+of these declarations:
+
+@smallexample
+[[vendor::safe]] void f();
+[[vendor::unsafe]] void f2();
+@end smallexample
+
 @item -Wno-builtin-declaration-mismatch
 @opindex Wno-builtin-declaration-mismatch
 @opindex Wbuiltin-declaration-mismatch
diff --git a/gcc/opts.c b/gcc/opts.c
index 1d2d22d7a3f..45db0de3f2e 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -2546,6 +2546,20 @@ common_handle_option (struct gcc_options *opts,
       /* Currently handled in a prescan.  */
       break;
 
+    case OPT_Wattributes_:
+      if (lang_mask == CL_DRIVER)
+	break;
+
+      if (value)
+	{
+	  warning_at (loc, 0, "arguments ignored for %<-Wattributes=%>; use "
+		      "%<-Wno-attributes=%> instead");
+	  break;
+	}
+
+      add_comma_separated_to_vector (&opts->x_flag_ignored_attributes, arg);
+      break;
+
     case OPT_Werror:
       dc->warning_as_error_requested = value;
       break;
diff --git a/gcc/plugin.h b/gcc/plugin.h
index 1640e253ca5..5556763d1bf 100644
--- a/gcc/plugin.h
+++ b/gcc/plugin.h
@@ -197,7 +197,9 @@ invoke_plugin_callbacks (int event ATTRIBUTE_UNUSED,
 /* In attribs.c.  */
 
 extern void register_attribute (const struct attribute_spec *attr);
+/* The default argument for the third parameter is given in attribs.h.  */
 extern struct scoped_attributes* register_scoped_attributes (const struct attribute_spec *,
-							     const char *);
+							     const char *,
+							     bool);
 
 #endif /* PLUGIN_H */
diff --git a/gcc/testsuite/c-c++-common/Wno-attributes-1.c b/gcc/testsuite/c-c++-common/Wno-attributes-1.c
new file mode 100644
index 00000000000..e28f1fbab17
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wno-attributes-1.c
@@ -0,0 +1,40 @@
+/* PR c++/101940 */
+/* { dg-do compile } */
+/* { dg-additional-options "-std=c++11" { target c++ } } */
+/* { dg-additional-options "-Wno-attributes=company::,yoyodyne::attr" } */
+/* { dg-additional-options "-Wno-attributes=c1::attr,c1::attr,c1::__attr__" } */
+/* { dg-additional-options "-Wno-attributes=clang" } */
+/* { dg-additional-options "-Wno-attributes=c2::,c2::attr" } */
+/* { dg-additional-options "-Wno-attributes=c3::attr,c3::" } */
+/* { dg-additional-options "-Wno-attributes=x::," } */
+/* { dg-additional-options "-Wno-attributes=yoyodyne::attr_new" } */
+/* { dg-additional-options "-Wno-attributes=c4::__attr__" } */
+
+[[company::attr]] void f1();
+[[company::attr2]] void f2();
+
+[[yoyodyne::attr]] void f3();
+[[yoyodyne::__attr__]] void f3__();
+[[yoyodyne::attrx]] void f4(); /* { dg-warning "ignored" } */
+[[yoyodyne::__attrx__]] void f4__(); /* { dg-warning "ignored" } */
+
+[[c1::attr]] void f5();
+
+[[c2::attr]] void f6();
+[[c2::attrx]] void f7();
+[[c2::__attr__]] void f6__();
+[[c2::__attrx__]] void f7__();
+
+[[c3::attr]] void f8();
+[[c3::attrx]] void f9();
+
+[[x::x]] void f10();
+
+[[yoyodyne::attr_new]] void f11();
+[[yoyodyne::__attr_new__]] void f11__();
+[[yoyodyne::attr_mew]] void f12(); /* { dg-warning "ignored" } */
+[[yoyodyne::__attr_mew__]] void f12__(); /* { dg-warning "ignored" } */
+
+[[c4::attr]] void f13();
+[[c4::__attr__]] void f13__();
+[[c4::attrx]] void f14(); /* { dg-warning "ignored" } */
diff --git a/gcc/testsuite/c-c++-common/Wno-attributes-2.c b/gcc/testsuite/c-c++-common/Wno-attributes-2.c
new file mode 100644
index 00000000000..1b08e972aed
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wno-attributes-2.c
@@ -0,0 +1,41 @@
+/* PR c++/101940 */
+/* { dg-do compile } */
+/* { dg-additional-options "-std=c++11" { target c++ } } */
+
+#pragma GCC diagnostic ignored_attributes "company::,yoyodyne::attr"
+#pragma GCC diagnostic ignored_attributes "c1::attr,c1::attr,c1::__attr__"
+#pragma GCC diagnostic ignored_attributes "clang"
+#pragma GCC diagnostic ignored_attributes "c2::,c2::attr"
+#pragma GCC diagnostic ignored_attributes "c3::attr,c3::"
+#pragma GCC diagnostic ignored_attributes "x::,"
+#pragma GCC diagnostic ignored_attributes "yoyodyne::attr_new"
+#pragma GCC diagnostic ignored_attributes "c4::__attr__"
+
+[[company::attr]] void f1();
+[[company::attr2]] void f2();
+
+[[yoyodyne::attr]] void f3();
+[[yoyodyne::__attr__]] void f3__();
+[[yoyodyne::attrx]] void f4(); /* { dg-warning "ignored" } */
+[[yoyodyne::__attrx__]] void f4__(); /* { dg-warning "ignored" } */
+
+[[c1::attr]] void f5();
+
+[[c2::attr]] void f6();
+[[c2::attrx]] void f7();
+[[c2::__attr__]] void f6__();
+[[c2::__attrx__]] void f7__();
+
+[[c3::attr]] void f8();
+[[c3::attrx]] void f9();
+
+[[x::x]] void f10();
+
+[[yoyodyne::attr_new]] void f11();
+[[yoyodyne::__attr_new__]] void f11__();
+[[yoyodyne::attr_mew]] void f12(); /* { dg-warning "ignored" } */
+[[yoyodyne::__attr_mew__]] void f12__(); /* { dg-warning "ignored" } */
+
+[[c4::attr]] void f13();
+[[c4::__attr__]] void f13__();
+[[c4::attrx]] void f14(); /* { dg-warning "ignored" } */

base-commit: 1949d7540a0322993bcae2f8893e2dbd29209040
-- 
2.31.1