RFA: fix for GDB C++ STABS problem

[Jim Blandy <jimb@redhat.com>]

Here's a fix for the GDB C++ STABS problem I just posted a test case
for.  This prevents `read_struct_type' from scribbling over an
existing definition, but it doesn't prevent `cleanup_undefined_types'
from producing bogus cv chains.  That's the next patch coming.

The real fix, of course, is to switch to Dwarf 2.

2002-05-01  Jim Blandy  <jimb@redhat.com>

	* stabsread.c (multiply_defined_struct): New complaint.
	(read_struct_type): If the type we were passed isn't empty, or
	incomplete, don't read the new struct type into it; complain,
	and return the original type unchanged.  Take a new `type_code'
	argument, which is the type code for the new type.
	(read_type): Rather than storing the type's type code here, pass
	it as an argument to read_struct_type, and let that take care of
	storing it.  That way, we don't overwrite the original type code,
	so read_struct_type can use it to decide whether we're overwriting
	something we shouldn't.
	(complain_about_struct_wipeout): New function.

Index: gdb/stabsread.c
===================================================================
RCS file: /cvs/src/src/gdb/stabsread.c,v
retrieving revision 1.30
diff -c -r1.30 stabsread.c
*** gdb/stabsread.c	21 Mar 2002 00:53:44 -0000	1.30
--- gdb/stabsread.c	1 May 2002 22:52:37 -0000
***************
*** 136,141 ****
--- 136,142 ----
  attach_fields_to_type (struct field_info *, struct type *, struct objfile *);
  
  static struct type *read_struct_type (char **, struct type *,
+                                       enum type_code,
  				      struct objfile *);
  
  static struct type *read_array_type (char **, struct type *,
***************
*** 235,240 ****
--- 236,244 ----
  static struct complaint unresolved_sym_chain_complaint =
  {"%s: common block `%s' from global_sym_chain unresolved", 0, 0};
  
+ static struct complaint multiply_defined_struct =
+ {"struct/union type gets multiply defined: %s%s", 0, 0};
+ 
  static struct complaint stabs_general_complaint =
  {"%s", 0, 0};
  
***************
*** 2801,2818 ****
  
      case 's':			/* Struct type */
      case 'u':			/* Union type */
!       type = dbx_alloc_type (typenums, objfile);
!       switch (type_descriptor)
! 	{
! 	case 's':
! 	  TYPE_CODE (type) = TYPE_CODE_STRUCT;
! 	  break;
! 	case 'u':
! 	  TYPE_CODE (type) = TYPE_CODE_UNION;
! 	  break;
! 	}
!       type = read_struct_type (pp, type, objfile);
!       break;
  
      case 'a':			/* Array type */
        if (**pp != 'r')
--- 2805,2825 ----
  
      case 's':			/* Struct type */
      case 'u':			/* Union type */
!       {
!         enum type_code type_code = TYPE_CODE_UNDEF;
!         type = dbx_alloc_type (typenums, objfile);
!         switch (type_descriptor)
!           {
!           case 's':
!             type_code = TYPE_CODE_STRUCT;
!             break;
!           case 'u':
!             type_code = TYPE_CODE_UNION;
!             break;
!           }
!         type = read_struct_type (pp, type, type_code, objfile);
!         break;
!       }
  
      case 'a':			/* Array type */
        if (**pp != 'r')
***************
*** 4156,4161 ****
--- 4163,4208 ----
    return 1;
  }
  
+ 
+ /* Sometimes GCC emits struct type forward references without the
+    necessary qualification.  If there's more than one definition for
+    different types that share the same unqualified name, GDB will
+    think they're both definitions of the same type, and try to wipe
+    out each earlier definition with it successor.
+ 
+    Complain that this is happening to TYPE.  */
+ static void 
+ complain_about_struct_wipeout (struct type *type)
+ {
+   char *name = "";
+   char *kind = "";
+ 
+   if (TYPE_TAG_NAME (type))
+     {
+       name = TYPE_TAG_NAME (type);
+       switch (TYPE_CODE (type))
+         {
+         case TYPE_CODE_STRUCT: kind = "struct "; break;
+         case TYPE_CODE_UNION:  kind = "union ";  break;
+         case TYPE_CODE_ENUM:   kind = "enum ";   break;
+         default: kind = "";
+         }
+     }
+   else if (TYPE_NAME (type))
+     {
+       name = TYPE_NAME (type);
+       kind = "";
+     }
+   else
+     {
+       name = "<unknown>";
+       kind = "";
+     }
+ 
+   complain (&multiply_defined_struct, kind, name);
+ }
+ 
+ 
  /* Read the description of a structure (or union type) and return an object
     describing the type.
  
***************
*** 4171,4177 ****
   */
  
  static struct type *
! read_struct_type (char **pp, struct type *type, struct objfile *objfile)
  {
    struct cleanup *back_to;
    struct field_info fi;
--- 4218,4225 ----
   */
  
  static struct type *
! read_struct_type (char **pp, struct type *type, enum type_code type_code,
!                   struct objfile *objfile)
  {
    struct cleanup *back_to;
    struct field_info fi;
***************
*** 4179,4187 ****
--- 4227,4250 ----
    fi.list = NULL;
    fi.fnlist = NULL;
  
+   /* Sometimes GCC emits struct type forward references without the
+      necessary qualification.  If there's more than one definition for
+      different types that share the same unqualified name, GDB will
+      think they're both definitions of the same type, and try to wipe
+      out each earlier definition with it successor.  */
+   if (! (TYPE_CODE (type) == TYPE_CODE_UNDEF
+          || TYPE_STUB (type)))
+     {
+       complain_about_struct_wipeout (type);
+ 
+       /* It's probably best to return the type unchanged.  */
+       return type;
+     }
+ 
    back_to = make_cleanup (null_cleanup, 0);
  
    INIT_CPLUS_SPECIFIC (type);
+   TYPE_CODE (type) = type_code;
    TYPE_FLAGS (type) &= ~TYPE_FLAG_STUB;
  
    /* First comes the total size in bytes.  */