Type nesting rule for extern, parser, control, and package types

[jaehyun1ee]

Section 7.2.8 defines the type nesting rules of P4. But it is not explicitly defined for extern, parser, control, and package types.

How about adding the following to the spec? I marked them as (new).

Element type \ Container type	header	header_union	struct or tuple	list	header stack
bit<W>	allowed	error	allowed	allowed	error
int<W>	allowed	error	allowed	allowed	error
varbit<W>	allowed	error	allowed	allowed	error
int	error	error	error	allowed	error
void	error	error	error	error	error
string	error	error	error	allowed	error
error	error	error	allowed	allowed	error
match_kind	error	error	error	allowed	error
bool	allowed	error	allowed	allowed	error
enumeration types	allowed	error	allowed	allowed	error
header types	error	allowed	allowed	allowed	allowed
header stacks	error	error	allowed	allowed	error
header unions	error	error	allowed	allowed	allowed
struct types	allowed	error	allowed	allowed	error
tuple types	error	error	allowed	allowed	error
list types	error	error	error	allowed	error
(new) extern types	error	error	error	error	error
(new) parser types	error	error	error	error	error
(new) control types	error	error	error	error	error
(new) package types	error	error	error	error	error

And for typedef and type,

Base type B	typedef B <name>	type B <name>
bit<W>	allowed	allowed
int<W>	allowed	allowed
varbit<W>	allowed	error
int	allowed	error
void	error	error
string	allowed	error
error	allowed	error
match_kind	error	error
bool	allowed	allowed
enumeration types	allowed	error
header types	allowed	error
header stacks	allowed	error
header unions	allowed	error
struct types	allowed	error
tuple types	allowed	error
list types	allowed	error
(new) extern types	allowed	error
(new) parser types	allowed	error
(new) control types	allowed	error
(new) package types	allowed	error
a typedef name	allowed	allowed
a type name	allowed	allowed

Allowing typedef for extern, parser, control, and package type is reflected on the following use cases in the p4c compiler test suite. (extern-inst-as-param.p4, issue2735-bmv2.p4, issue2735.p4, and typedef-constructor.p4)

extern MyCounter<I> {
    MyCounter(bit<32> size);
    void count(in I index);
}
typedef bit<10> my_counter_index_t;
typedef MyCounter<my_counter_index_t> my_counter_t;

And when those types are aliased, it must be that all the type variables are bound.

[jafingerhut]

Adding the new entries you describe in those tables looks reasonable to me. Thanks for the links to relevant test cases in the existing p4c test suite.