[PATCH] add __attribute__ ((designated_init))

[Tom Tromey <tromey at redhat dot com>]

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

The name of the attribute and the option were chosen to be compatible
with sparse.  I added this warning to -Wall since it seemed like the
kind of warning users would ordinarily want -- if they are not using
the attribute, they won't ever see it anyhow.

I wrote a new test case covering the same cases that the sparse test
case covers.  I also added tests for applying the attribute to
non-struct types; note that in this case sparse issues a warning but
gcc issues an error.  I think an error is more appropriate.

Built and regtested on x86-64 Fedora 20.  It's been a while but I
think I did it properly.

Tom
---
 gcc/ChangeLog                           |  7 +++
 gcc/c-family/ChangeLog                  |  7 +++
 gcc/c-family/c-common.c                 | 17 +++++++
 gcc/c-family/c.opt                      |  4 ++
 gcc/c/ChangeLog                         |  9 ++++
 gcc/c/c-typeck.c                        | 12 +++++
 gcc/doc/extend.texi                     | 11 +++++
 gcc/doc/invoke.texi                     | 10 +++-
 gcc/testsuite/ChangeLog                 |  5 ++
 gcc/testsuite/gcc.dg/Wdesignated-init.c | 82 +++++++++++++++++++++++++++++++++
 10 files changed, 163 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/Wdesignated-init.c

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 652d2c9..77e4d54 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2014-01-20  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.
+
 2014-01-19  John David Anglin  <danglin@gcc.gnu.org>
 
 	* config/pa/pa.c (pa_attr_length_millicode_call): Correct length of
diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index fede01f..7593791 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,10 @@
+2014-01-20  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.
+
 2014-01-15  Laurent Alfonsi <laurent.alfonsi@st.com>
 
 	PR c++/49718
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 35958ea..e0a0653 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -377,6 +377,7 @@ 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 (tree *, tree, tree, int, bool *);
 
 static void check_function_nonnull (tree, int, tree *);
 static void check_nonnull_arg (void *, tree, unsigned HOST_WIDE_INT);
@@ -766,6 +767,8 @@ const struct attribute_spec c_common_attribute_table[] =
 			      handle_omp_declare_simd_attribute, false },
   { "omp declare target",     0, 0, true, false, false,
 			      handle_omp_declare_target_attribute, false },
+  { "designated_init",        0, 0, false, true, false,
+			      handle_designated_init, false },
   { NULL,                     0, 0, false, false, false, NULL, false }
 };
 
@@ -9133,6 +9136,20 @@ 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 (tree *node, tree, tree, int, bool *no_add_attrs)
+{
+  if (TREE_CODE (*node) != RECORD_TYPE)
+    {
+      error ("designated_init attribute is only valid on struct type");
+      *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 38ae58e..29ac4d0 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -355,6 +355,10 @@ 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(0) Warning LangEnabledBy(C ObjC,Wall)
+Warn about positional initialization of structs requiring designated initializers
+
 Wdiv-by-zero
 C ObjC C++ ObjC++ Var(warn_div_by_zero) Init(1) Warning
 Warn about compile-time integer division by zero
diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index 4754bdf..c34fe93 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,12 @@
+2014-01-20  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.
+
 2014-01-15  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c/58943
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 09049e2..31a1f5a 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -6885,6 +6885,7 @@ struct constructor_stack
   char outer;
   char incremental;
   char designated;
+  int designator_depth;
 };
 
 static struct constructor_stack *constructor_stack;
@@ -7056,6 +7057,7 @@ 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;
 
@@ -7201,6 +7203,7 @@ push_init_level (int implicit, struct obstack * braced_init_obstack)
   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;
@@ -7501,6 +7504,7 @@ pop_init_level (int implicit, struct obstack * braced_init_obstack)
   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)
@@ -8558,6 +8562,14 @@ process_init_element (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 (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 2f4f91d..7cefeb1 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -5742,6 +5742,17 @@ 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 struct 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 only emits a warning for this attribute when
+@option{-Wdesignated-init} is given.
+
 @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 ac4b597..fd5fb18 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -241,7 +241,8 @@ 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-deprecated -Wno-deprecated-declarations @gol
+-Wdesignated-init -Wdisabled-optimization  @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
@@ -3340,6 +3341,7 @@ Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
 -Warray-bounds @r{(only with} @option{-O2}@r{)}  @gol
 -Wc++11-compat  @gol
 -Wchar-subscripts  @gol
+-Wdesignated-init @gol
 -Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol
 -Wimplicit-int @r{(C and Objective-C only)} @gol
 -Wimplicit-function-declaration @r{(C and Objective-C only)} @gol
@@ -5094,6 +5096,12 @@ 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 -Wdesignated-init @r{(C and Objective-C only)}
+Issue a warning 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/ChangeLog b/gcc/testsuite/ChangeLog
index 665280c..57eea75 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2014-01-20  Tom Tromey  <tromey@redhat.com>
+
+	PR c/59855
+	* gcc.dg/Wdesignated-init.c: New file.
+
 2014-01-19  Uros Bizjak  <ubizjak@gmail.com>
 
 	* g++.dg/pr49718.C: Add "-mno-explicit-relocs" for alpha*-*-* targets.
diff --git a/gcc/testsuite/gcc.dg/Wdesignated-init.c b/gcc/testsuite/gcc.dg/Wdesignated-init.c
new file mode 100644
index 0000000..72cda8b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wdesignated-init.c
@@ -0,0 +1,82 @@
+/* PR c/59855 */
+/* { dg-do compile } */
+/* { dg-options "-Wdesignated-init" } */
+
+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 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 Des da[] = {
+  { .x = 1, .y = 2 },
+  { 5, 5 } /* { dg-warning "(positional|near initialization)" } */
+};
-- 
1.8.4.2