Implement -var-info-path-expression.

* mi/mi-cmds.h (mi_cmd_var_info_path_expression):
	Declare.
	* mi/mi-cmds.c (mi_cmds): Register var-info-path-expression.
	* mi/mi-cmd-var.c (mi_cmd_var_info_path_expression): New.
	* varobj.c (struct varobj): New field 'path_expr'.
	(c_path_expr_of_child, cplus_path_expr_of_child)
	(java_path_expr_of_child): New.
	(struct language_specific): New field path_expr_of_child.
	(varobj_create): Initialize the path_expr field.
	(varobj_get_path_expr): New.
	(new_variable): Initialize the path_expr field.
	(free_variable): Free the path_expr field.
	(adjust_value_for_children_access): New parameter
	WAS_TYPE.
	(c_number_of_children): Adjust.
	(c_describe_child): New parameter CFULL_EXPRESSION.
	Compute full expression.
	(c_value_of_child, c_type_of_child): Adjust.
	(cplus_number_of_children): Adjust.
	(cplus_describe_child): New parameter CFULL_EXPRESSION.
	Compute full expression.
	(cplus_name_of_child, cplus_value_of_child)
	(cplus_type_of_child): Adjust.
	* varobj.h (varobj_get_path_expr): Declare.

gdb/doc/ChangeLog

@@ -1,3 +1,9 @@
+2007-08-31  Vladimir Prus  <vladimir@codesourcery.com>
+
+	* gdb.texinfo (Variable Objects): Adjust docs
+	for -var-info-expression and document
+	-var-info-path-expression.
+
 2007-08-20  Jim Blandy  <jimb@codesourcery.com>
 
 	* gdb.texinfo (Top): Dedicate manual to the memory of Fred Fish.

gdb/doc/gdb.texinfo

@@ -19312,7 +19312,9 @@ access this functionality:
 @item @code{-var-info-type}
 @tab show the type of this variable object
 @item @code{-var-info-expression}
-@tab print what this variable object represents
+@tab print parent-relative expression that this variable object represents
+@item @code{-var-info-path-expression}
+@tab print full expression that this variable object represents
 @item @code{-var-show-attributes}
 @tab is this variable editable? does it exist here?
 @item @code{-var-evaluate-expression}
@@ -19513,14 +19515,50 @@ returned as a string in the same format as it is output by the
  -var-info-expression @var{name}
 @end smallexample
 
-Returns what is represented by the variable object @var{name}:
+Returns a string that is suitable for presenting this
+variable object in user interface.  The string is generally
+not valid expression in the current language, and cannot be evaluated.
+
+For example, if @code{a} is an array, and variable object
+@code{A} was created for @code{a}, then we'll get this output:
 
 @smallexample
- lang=@var{lang-spec},exp=@var{expression}
+(gdb) -var-info-expression A.1
+^done,lang="C",exp="1"
 @end smallexample
 
 @noindent
-where @var{lang-spec} is @code{@{"C" | "C++" | "Java"@}}.
+Here, the values of @code{lang} can be @code{@{"C" | "C++" | "Java"@}}.
+
+Note that the output of the @code{-var-list-children} command also
+includes those expressions, so the @code{-var-info-expression} command
+is of limited use.
+
+@subheading The @code{-var-info-path-expression} Command
+@findex -var-info-path-expression
+
+@subsubheading Synopsis
+
+@smallexample
+ -var-info-path-expression @var{name}
+@end smallexample
+
+Returns an expression that can be evaluated in the current
+context and will yield the same value that a variable object has.
+Compare this with the @code{-var-info-expression} command, which
+result can be used only for UI presentation.  Typical use of
+the @code{-var-info-path-expression} command is creating a 
+watchpoint from a variable object.
+
+For example, suppose @code{C} is a C@t{++} class, derived from class
+@code{Base}, and that the @code{Base} class has a member called
+@code{m_size}.  Assume a variable @code{c} is has the type of
+@code{C} and a variable object @code{C} was created for variable
+@code{c}.  Then, we'll get this output:
+@smallexample
+(gdb) -var-info-path-expression C.Base.public.m_size
+^done,path_expr=((Base)c).m_size)
+@end smallexample
 
 @subheading The @code{-var-show-attributes} Command
 @findex -var-show-attributes