[Bro-Dev] consistency checking for attributes

[Vern Paxson]

Attributes currently receive essentially no consistency checking.
For example, executing this script:

	global a: count
		&default = 10
		&default = 9
		&optional
		&log
		&add_func = function(d: double, t: time): count { return 3; };
	print a;

simply results in:

error in /Users/vern/tmp/attr-type-check.bro, line 7: value used but not set (a)

I'm planning to add basic consistency checking, which will look for
(1) attributes that are repeated (which doesn't appear to be meaningful for
any of them) and (2) attributes that don't make sense in a given context,
like the ones listed above.

I'm thinking of implementing this as an internal table of meta-attributes,
i.e., each attribute type, like ATTR_OPTIONAL, will have its own attributes
like whether it requires a record context, only makes sense for aggregates,
etc.  Here are the ones that come to mind, based on looking at the attributes
at https://www.bro.org/sphinx/script-reference/attributes.html with examples
in parens:

	applies to global variable	(&redef)
		to global type		(&redef)
		to event handler	(&priority)
		to record field		(&log)
		to indexed type		(&default)
		to global indexed type	(&add_func)
		to type with expirable entries	(&expire_func)
		to a file		(&rotate_interval)

Any feedback?

		Vern