c: -Wmissing-field-initializers and designated inits [PR82283, PR84685]

This patch fixes two kinds of wrong -Wmissing-field-initializers
warnings.  Our docs say that this warning "does not warn about designated
initializers", but we give a warning for

1) the array case:

  struct S {
    struct N {
      int a;
      int b;
    } c[1];
  } d = {
    .c[0].a = 1,
    .c[0].b = 1, // missing initializer for field 'b' of 'struct N'
  };

we warn because push_init_level, when constructing an array, clears
constructor_designated (which the warning relies on), and we forget
that we were in a designated initializer context.  Fixed by the
push_init_level hunk; and

2) the compound literal case:

  struct T {
    int a;
    int *b;
    int c;
  };

  struct T t = { .b = (int[]){1} }; // missing initializer for field 'c' of 'struct T'

where set_designator properly sets constructor_designated to 1, but the
compound literal causes us to create a whole new initializer_stack in
start_init, which clears constructor_designated.  Then, after we've parsed
the compound literal, finish_init flushes the initializer_stack entry,
but doesn't restore constructor_designated, so we forget we were in
a designated initializer context, which causes the bogus warning.  (The
designated flag is also tracked in constructor_stack, but in this case,
we didn't perform push_init_level between set_designator and start_init
so it wasn't saved anywhere.)

	PR c/82283
	PR c/84685

gcc/c/ChangeLog:

	* c-typeck.cc (struct initializer_stack): Add 'designated' member.
	(start_init): Set it.
	(finish_init): Restore constructor_designated.
	(push_init_level): Set constructor_designated to the value of
	constructor_designated in the upper constructor_stack.

gcc/testsuite/ChangeLog:

	* gcc.dg/Wmissing-field-initializers-1.c: New test.
	* gcc.dg/Wmissing-field-initializers-2.c: New test.
	* gcc.dg/Wmissing-field-initializers-3.c: New test.
	* gcc.dg/Wmissing-field-initializers-4.c: New test.
	* gcc.dg/Wmissing-field-initializers-5.c: New test.

1 files changed, 6 insertions, 4 deletions

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index c0812de84b4..6c4af5e4cde 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -8438,6 +8438,7 @@ struct initializer_stack
   char top_level;
   char require_constant_value;
   char require_constant_elements;
+  char designated;
   rich_location *missing_brace_richloc;
 };
 
@@ -8464,6 +8465,7 @@ start_init (tree decl, tree asmspec_tree ATTRIBUTE_UNUSED, int top_level,
   p->top_level = constructor_top_level;
   p->next = initializer_stack;
   p->missing_brace_richloc = richloc;
+  p->designated = constructor_designated;
   initializer_stack = p;
 
   constructor_decl = decl;
@@ -8522,6 +8524,7 @@ finish_init (void)
   require_constant_value = p->require_constant_value;
   require_constant_elements = p->require_constant_elements;
   constructor_stack = p->constructor_stack;
+  constructor_designated = p->designated;
   constructor_range_stack = p->constructor_range_stack;
   constructor_elements = p->elements;
   spelling = p->spelling;
@@ -8731,7 +8734,9 @@ push_init_level (location_t loc, int implicit,
   constructor_depth = SPELLING_DEPTH ();
   constructor_elements = NULL;
   constructor_incremental = 1;
-  constructor_designated = 0;
+  /* If the upper initializer is designated, then mark this as
+     designated too to prevent bogus warnings.  */
+  constructor_designated = p->designated;
   constructor_pending_elts = 0;
   if (!implicit)
     {
@@ -8756,9 +8761,6 @@ push_init_level (location_t loc, int implicit,
 	  push_member_name (constructor_fields);
 	  constructor_depth++;
 	}
-      /* If upper initializer is designated, then mark this as
-	 designated too to prevent bogus warnings.  */
-      constructor_designated = p->designated;
     }
   else if (TREE_CODE (constructor_type) == ARRAY_TYPE)
     {