2008-07-27   Rob Quill <rob.quill@gmail.com>

	Add $in_scope as a type of expression.
	* c-exp.y (IN_SCOPE): New token.
	  (exp): IN_SCOPE (name): evaluates to 1 if name is in scope,
	  0 otherwise.
	(yylex): Match "$in_scope" as IN_SCOPE token
       * gdb.texinfo (expressions): Add a small paragraph (with an
	 example) about the $in_scope operator.
       * NEWS: Mentions $in_scope.

Index: gdb/NEWS
===================================================================
RCS file: /cvs/src/src/gdb/NEWS,v
retrieving revision 1.282
diff -u -p -r1.282 NEWS
--- gdb/NEWS	18 Jul 2008 20:55:32 -0000	1.282
+++ gdb/NEWS	27 Jul 2008 23:02:48 -0000
@@ -3,6 +3,12 @@
 
 *** Changes since GDB 6.8
 
+* New expression type
+
+$in_scope(...)
+  The value of this expression is 1 if the variable within the
+  parentheses is within the current scope, 0 otherwise.
+
 * Commands `set debug-file-directory', `set solib-search-path' and `set args'
 now complete on file names.
 
Index: gdb/c-exp.y
===================================================================
RCS file: /cvs/src/src/gdb/c-exp.y,v
retrieving revision 1.46
diff -u -p -r1.46 c-exp.y
--- gdb/c-exp.y	25 Jun 2008 15:49:20 -0000	1.46
+++ gdb/c-exp.y	27 Jul 2008 23:02:49 -0000
@@ -209,6 +209,8 @@ static int parse_number (char *, int, in
 %token TRUEKEYWORD
 %token FALSEKEYWORD
 
+/* $in_scope opperator */
+%token IN_SCOPE
 
 %left ','
 %left ABOVE_COMMA
@@ -252,6 +254,30 @@ exp1	:	exp
 	;
 
 /* Expressions, not including the comma operator.  */
+exp    :       IN_SCOPE '(' name_not_typename ')'
+                       {
+                         struct type *int_type;
+                         struct minimal_symbol *min_symbol;
+
+                         /* If there are no symbols then just stop right away */
+                         if (!have_full_symbols () && !have_partial_symbols ())
+                           error ("No symbol table is loaded.  Use the \"file\" command.");
+
+                         /* Otherwise, prepare to write out the value */
+                         int_type = builtin_type (current_gdbarch)->builtin_int;
+                         write_exp_elt_opcode (OP_LONG);
+                         write_exp_elt_type (int_type);
+
+                         min_symbol =
+                           lookup_minimal_symbol (copy_name($3.stoken), NULL, NULL);
+                         if ($3.sym || min_symbol)
+                           write_exp_elt_longcst ((LONGEST) 1);
+                         else
+                           write_exp_elt_longcst ((LONGEST) 0);
+
+                         write_exp_elt_opcode (OP_LONG); }
+       ;
+
 exp	:	'*' exp    %prec UNARY
 			{ write_exp_elt_opcode (UNOP_IND); }
 	;
@@ -1739,6 +1765,9 @@ yylex ()
   /* Catch specific keywords.  Should be done with a data structure.  */
   switch (namelen)
     {
+    case 9:
+      if (strncmp (tokstart, "$in_scope", 9) == 0)
+        return IN_SCOPE;
     case 8:
       if (strncmp (tokstart, "unsigned", 8) == 0)
 	return UNSIGNED;
Index: gdb/doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.509
diff -u -p -r1.509 gdb.texinfo
--- gdb/doc/gdb.texinfo	18 Jul 2008 20:55:33 -0000	1.509
+++ gdb/doc/gdb.texinfo	27 Jul 2008 23:03:11 -0000
@@ -5750,6 +5750,24 @@ memory.  @var{addr} may be any expressio
 pointer (but parentheses are required around binary operators, just as in
 a cast).  This construct is allowed regardless of what kind of data is
 normally supposed to reside at @var{addr}.
+
+@vindex $in_scope
+@cindex variable in scope, testing
+@item $in_scope
+@samp{$in_scope} allows you to check if a variable is in scope,
+returning 1 if it is and 0 if it is not.  This is most useful when scripting @value{GDBN}
+as it means that the script will not stop executing if a variable is not in scope,
+provided that you check if it is in scope before you test its value.  The operator
+only works on variables and will not work on structure members or array elements
+for instance.
+
+An example usage from a GDB script may be:
+
+@smallexample
+if ($in_scope(a) == 1 && $in_scope(b) == 1)
+  print a+b  
+@end smallexample
+
 @end table
 
 @node Ambiguous Expressions