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Re: [PATCH] add __attribute__ ((designated_init))


>>>>> "Joseph" == Joseph S Myers <joseph@codesourcery.com> writes:

[...]

Joseph> Is there a reason someone using the attribute might not want the
Joseph> warning?  That is, why isn't -Wdesignated-init enabled by
Joseph> default, given that it's only relevant to people using an
Joseph> attribute whose sole function relates to the warning?

I've finally updated this patch.  I think I've addressed all the review
comments.

For reference the original thread is here:

        https://gcc.gnu.org/ml/gcc-patches/2014-01/msg01284.html

This adds __attribute__((designated_init)) and -Wdesignated-init, a
feature from sparse.  This is also PR c/59855.

Tom

2014-07-01  Tom Tromey  <tromey@redhat.com>

	PR c/59855
	* doc/invoke.texi (Warning Options): Document -Wdesignated-init.
	* doc/extend.texi (Type Attributes): Document designated_init
	attribute.

2014-07-01  Tom Tromey  <tromey@redhat.com>

	PR c/59855
	* c.opt (Wdesignated-init): New option.
	* c-common.c (c_common_attribute_table): Add "designated_init".
	(handle_designated_init): New function.

2014-07-01  Tom Tromey  <tromey@redhat.com>

	* c-typeck.c (struct constructor_stack) <designator_depth>: New
	field.
	(really_start_incremental_init, push_init_level): Initialize
	designator_depth.
	(pop_init_level): Set global designator_depth.
	(process_init_element): Check for designated_init attribute.

2014-07-01  Tom Tromey  <tromey@redhat.com>

	PR c/59855
	* gcc.dg/Wdesignated-init.c: New file.

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index ee89fca..79d0f2f 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -380,6 +380,7 @@ static tree handle_omp_declare_simd_attribute (tree *, tree, tree, int,
 					       bool *);
 static tree handle_omp_declare_target_attribute (tree *, tree, tree, int,
 						 bool *);
+static tree handle_designated_init_attribute (tree *, tree, tree, int, bool *);
 
 static void check_function_nonnull (tree, int, tree *);
 static void check_nonnull_arg (void *, tree, unsigned HOST_WIDE_INT);
@@ -773,6 +774,8 @@ const struct attribute_spec c_common_attribute_table[] =
 			      handle_alloc_align_attribute, false },
   { "assume_aligned",	      1, 2, false, true, true,
 			      handle_assume_aligned_attribute, false },
+  { "designated_init",        0, 0, false, true, false,
+			      handle_designated_init_attribute, false },
   { NULL,                     0, 0, false, false, false, NULL, false }
 };
 
@@ -9275,6 +9278,21 @@ handle_returns_nonnull_attribute (tree *node, tree, tree, int,
   return NULL_TREE;
 }
 
+/* Handle a "designated_init" attribute; arguments as in
+   struct attribute_spec.handler.  */
+
+static tree
+handle_designated_init_attribute (tree *node, tree name, tree, int,
+				  bool *no_add_attrs)
+{
+  if (TREE_CODE (*node) != RECORD_TYPE)
+    {
+      error ("%qE attribute is only valid on %<struct%> type", name);
+      *no_add_attrs = true;
+    }
+  return NULL_TREE;
+}
+
 
 /* Check for valid arguments being passed to a function with FNTYPE.
    There are NARGS arguments in the array ARGARRAY.  */
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index c89040a..6517790 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -359,6 +359,10 @@ Wdeprecated
 C C++ ObjC ObjC++ Var(warn_deprecated) Init(1) Warning
 Warn if a deprecated compiler feature, class, method, or field is used
 
+Wdesignated-init
+C ObjC Var(warn_designated_init) Init(1) Warning
+Warn about positional initialization of structs requiring designated initializers
+
 Wdiscarded-qualifiers
 C ObjC Var(warn_discarded_qualifiers) Init(1) Warning
 Warn if type qualifiers on pointers are discarded
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 35bfd14..c0f3912 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -6946,6 +6946,7 @@ struct constructor_stack
   char outer;
   char incremental;
   char designated;
+  int designator_depth;
 };
 
 static struct constructor_stack *constructor_stack;
@@ -7117,6 +7118,7 @@ really_start_incremental_init (tree type)
   p->outer = 0;
   p->incremental = constructor_incremental;
   p->designated = constructor_designated;
+  p->designator_depth = designator_depth;
   p->next = 0;
   constructor_stack = p;
 
@@ -7266,6 +7268,7 @@ push_init_level (location_t loc, int implicit,
   p->outer = 0;
   p->incremental = constructor_incremental;
   p->designated = constructor_designated;
+  p->designator_depth = designator_depth;
   p->next = constructor_stack;
   p->range_stack = 0;
   constructor_stack = p;
@@ -7573,6 +7576,7 @@ pop_init_level (location_t loc, int implicit,
   constructor_erroneous = p->erroneous;
   constructor_incremental = p->incremental;
   constructor_designated = p->designated;
+  designator_depth = p->designator_depth;
   constructor_pending_elts = p->pending_elts;
   constructor_depth = p->depth;
   if (!p->implicit)
@@ -8642,6 +8646,15 @@ process_init_element (location_t loc, struct c_expr value, bool implicit,
   if (constructor_type == 0)
     return;
 
+  if (!implicit && warn_designated_init && !was_designated
+      && TREE_CODE (constructor_type) == RECORD_TYPE
+      && lookup_attribute ("designated_init",
+			   TYPE_ATTRIBUTES (constructor_type)))
+    warning_init (loc,
+		  OPT_Wdesignated_init,
+		  "positional initialization of field "
+		  "in %<struct%> declared with %<designated_init%> attribute");
+
   /* If we've exhausted any levels that didn't have braces,
      pop them now.  */
   while (constructor_stack->implicit)
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index cdfcce7..889cc0b 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -5886,6 +5886,17 @@ and caught in another, the class must have default visibility.
 Otherwise the two shared objects are unable to use the same
 typeinfo node and exception handling will break.
 
+@item designated_init
+This attribute may only be applied to structure types.  It indicates
+that any initialization of an object of this type must use designated
+initializers rather than positional initializers.  The intent of this
+attribute is to allow the programmer to indicate that a structure's
+layout may change, and that therefore relying on positional
+initialization will result in future breakage.
+
+GCC emits warnings based on this attribute by default; use
+@option{-Wno-designated-init} to suppress them.
+
 @end table
 
 To specify multiple attributes, separate them by commas within the
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index b1f6f4b..7fedd37 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -243,8 +243,8 @@ Objective-C and Objective-C++ Dialects}.
 -Wc++-compat -Wc++11-compat -Wcast-align  -Wcast-qual  @gol
 -Wchar-subscripts -Wclobbered  -Wcomment -Wconditionally-supported  @gol
 -Wconversion -Wcoverage-mismatch -Wdate-time -Wdelete-incomplete -Wno-cpp  @gol
--Wno-deprecated -Wno-deprecated-declarations -Wdisabled-optimization  @gol
--Wno-discarded-qualifiers @gol
+-Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init @gol
+-Wdisabled-optimization -Wno-discarded-qualifiers @gol
 -Wno-div-by-zero -Wdouble-promotion -Wempty-body  -Wenum-compare @gol
 -Wno-endif-labels -Werror  -Werror=* @gol
 -Wfatal-errors  -Wfloat-equal  -Wformat  -Wformat=2 @gol
@@ -5144,6 +5144,12 @@ a suffix.  When used together with @option{-Wsystem-headers} it
 warns about such constants in system header files.  This can be useful
 when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma
 from the decimal floating-point extension to C99.
+
+@item -Wno-designated-init @r{(C and Objective-C only)}
+Suppress warnings when a positional initializer is used to initialize
+a structure that has been marked with the @code{designated_init}
+attribute.
+
 @end table
 
 @node Debugging Options
diff --git a/gcc/testsuite/gcc.dg/Wdesignated-init.c b/gcc/testsuite/gcc.dg/Wdesignated-init.c
new file mode 100644
index 0000000..b9ca572
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wdesignated-init.c
@@ -0,0 +1,107 @@
+/* PR c/59855 */
+/* { dg-do compile } */
+/* { dg-options "-std=gnu99" } */
+
+typedef int vvv  __attribute__((designated_init)); /* { dg-error "only valid" } */
+
+union U {
+  int a;
+  double b;
+} __attribute__((designated_init)); /* { dg-error "only valid" } */
+
+enum E { ONE, TWO }  __attribute__((designated_init)); /* { dg-error "only valid" } */
+
+struct Pok {
+  int x;
+  int y;
+};
+
+struct Des {
+  int x;
+  int y;
+} __attribute__ ((designated_init));
+
+struct Des d1 = { 5, 5 }; /* { dg-warning "(positional|near initialization)" } */
+struct Des d2 = { .x = 5, .y = 5 };
+struct Des d3 = { .x = 5, 5 }; /* { dg-warning "(positional|near initialization)" } */
+
+struct Des fd1 (void)
+{
+  return (struct Des) { 5, 5 }; /* { dg-warning "(positional|near initialization)" } */
+}
+
+struct Des fd2 (void)
+{
+  return (struct Des) { .x = 5, .y = 5 };
+}
+
+struct Des fd3 (void)
+{
+  return (struct Des) { .x = 5, 5 }; /* { dg-warning "(positional|near initialization)" } */
+}
+
+struct Wrap {
+  struct Pok p;
+  struct Des d;
+} __attribute__ ((designated_init));
+
+struct Wrap w1 = { { 0, 1 }, { 2, 3} }; /* { dg-warning "(positional|near initialization)" } */
+struct Wrap w2 = { .p = { 0, 1 }, { 2, 3} }; /* { dg-warning "(positional|near initialization)" } */
+struct Wrap w3 = { .p = { 0, 1 }, .d = { 2, 3} }; /* { dg-warning "(positional|near initialization)" } */
+struct Wrap w4 = { { 0, 1 }, .d = { 2, 3} }; /* { dg-warning "(positional|near initialization)" } */
+struct Wrap w5 = { .p = { 0, 1 }, .d = { .x = 2, .y = 3} };
+
+struct Wrap w6 = { { 0, 1 }, .d.x = 2, .d.y = 3 }; /* { dg-warning "(positional|near initialization)" } */
+struct Wrap w7 = { .p = { 0, 1 }, .d.x = 2, .d.y = 3 };
+struct Wrap w8 = { .p = { 0, 1 }, .d = { 2, 0 }, .d.y = 3 }; /* { dg-warning "(positional|near initialization)" } */
+struct Wrap w9 = { .p = { 0, 1 }, .d = { .x = 2 }, .d.y = 3 };
+
+struct Wrap fw1 (void)
+{
+  return (struct Wrap) { { 0, 1 }, { 2, 3} }; /* { dg-warning "(positional|near initialization)" } */
+};
+
+struct Wrap fw2 (void)
+{
+  return (struct Wrap) { .p = { 0, 1 }, { 2, 3} }; /* { dg-warning "(positional|near initialization)" } */
+}
+
+struct Wrap fw3 (void)
+{
+  return (struct Wrap) { .p = { 0, 1 }, .d = { 2, 3} }; /* { dg-warning "(positional|near initialization)" } */
+}
+
+struct Wrap fw4 (void)
+{
+  return (struct Wrap) { { 0, 1 }, .d = { 2, 3} }; /* { dg-warning "(positional|near initialization)" } */
+}
+
+struct Wrap fw5 (void)
+{
+  return (struct Wrap) { .p = { 0, 1 }, .d = { .x = 2, .y = 3} };
+}
+
+struct Wrap fw6 (void)
+{
+  return (struct Wrap) { { 0, 1 }, .d.x = 2, .d.y = 3 }; /* { dg-warning "(positional|near initialization)" } */
+}
+
+struct Wrap fw7 (void)
+{
+  return (struct Wrap) { .p = { 0, 1 }, .d.x = 2, .d.y = 3 };
+}
+
+struct Wrap fw8 (void)
+{
+  return (struct Wrap) { .p = { 0, 1 }, .d = { 2, 0 }, .d.y = 3 }; /* { dg-warning "(positional|near initialization)" } */
+}
+
+struct Wrap fw9 (void)
+{
+  return (struct Wrap) { .p = { 0, 1 }, .d = { .x = 2 }, .d.y = 3 };
+}
+
+struct Des da[] = {
+  { .x = 1, .y = 2 },
+  { 5, 5 } /* { dg-warning "(positional|near initialization)" } */
+};


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