Add support for Disjoint Normal Form (DNF) types

[Girgias]

RFC: https://wiki.php.net/rfc/dnf_types

This allows to combine union and intersection types together in the following form (A&B)|(X&Y)|T but not of the form (X|A)&(Y|B) or (X|A)&(Y|B)|T.

[arnaud-lb]

In the second form it may be unclear why the type being less restrictive is a problem. At first I though it was going to be a variance issue when reading https://github.com/php/php-src/pull/8725/files#diff-d73c373701c7d0e7cb2a5fbc3b3a0843746d028029531ad73dd3024676a0a6d0

Something like "Type A&B is redundant because it is less restrictive than A" would make this clearer to me. This also puts the emphasis on A&B, and gives a hint at how the problem could be resolved (by removing the redundant type).

Maybe displaying the full union type would help as well: "Member A&B in union A&B|A is redundant because it is less restrictive than A". (Other union/intersection messages do not appear to display the full union type though.)

[Girgias]

The problem is we might not know the full union type indeed imagine a union type of the form:
A|(A&B)|C the compile warning would be emitted when parsing (A&B) but at this point we have no knowledge of the |C part and would not be able to display the complete type anyway.

But I know that I read the error message again I do agree it is kinda confusing so I will improve it

[Girgias]

Note: To fail the XFAIL test use the: make test TESTS="Zend/tests/type_declarations/ -j8 -d opcache.enable_cli=1" command.
I've narrowed down the problem to the inheritance cache, but I can't figure out where the issue is.

The Travis CI Failure can be reproduced with: make test USE_ZEND_ALLOC=0 TESTS="ext/reflection/tests/types/ --repeat 2 -j8 -d opcache.enable_cli=1 --asan"

[arnaud-lb]

On the XFAIL: OPcache expects class names in the dependency list to be shm-allocated / persisted. The name that fails the assertion was added to the list by track_class_dependency(), called by zend_is_intersection_subtype_of_class(), and comes from a method arg infos. Normally the class names in arg infos are persisted by OPcache before this step, but here it didn't happen. I think that we need to update zend_persist_type(): it doesn't appear to recurse in nested lists (zend_persist_type_calc() would need to be updated as well).

[arnaud-lb]

There are a few other places that may or may not need to be updated: zend_mark_function_as_generator, zend_type_permits_self, zend_declare_typed_property, and so on.

There could be a use-case for a ZEND_TYPE_FOREACH_CLASS_NAME() macro.

[Girgias]

On the XFAIL: OPcache expects class names in the dependency list to be shm-allocated / persisted. The name that fails the assertion was added to the list by track_class_dependency(), called by zend_is_intersection_subtype_of_class(), and comes from a method arg infos. Normally the class names in arg infos are persisted by OPcache before this step, but here it didn't happen. I think that we need to update zend_persist_type(): it doesn't appear to recurse in nested lists (zend_persist_type_calc() would need to be updated as well).

So that was the issue, I was looking at the wrong place then.
I think I fixed the issues for that now then.

There are a few other places that may or may not need to be updated: zend_mark_function_as_generator, zend_type_permits_self, zend_declare_typed_property, and so on.

There could be a use-case for a ZEND_TYPE_FOREACH_CLASS_NAME() macro.

I'm not sure how a ZEND_TYPE_FOREACH_CLASS_NAME() macro would work as I think it's a general problem with ZEND_TYPE_FOREACH() which needs to cater to the nested types.

I will try to come up with test cases for every other instance as those probably do have some issue lingering in disguise

[sgolemon]

It's not letting me comment direcly on the patch, but I had some minor thoughts about making the parser a tiny bit more readable (less verbose):

union_type_element:
                type { $$ = $1; }
        |        '(' intersection_type ')' { $$ = $2; }
;

union_type:
		union_type_element '|' union_type_element
			{ $$ = zend_ast_create_list(2, ZEND_AST_TYPE_UNION, $1, $3); }
	|	union_type '|' union_type_element
			{ $$ = zend_ast_list_add($1, $3); }
;

And of course:

union_type_without_static_element:
                type_without_static { $$ = $1; }
        |        '(' intersection_type_without_static ')' { $$ = $2; }
;

union_type_without_static:
		union_type_without_static_element '|' union_type_without_static_element
			{ $$ = zend_ast_create_list(2, ZEND_AST_TYPE_UNION, $1, $3); }
	|	union_type_without_static '|' union_type_without_static_element
			{ $$ = zend_ast_list_add($1, $3); }
;

The lower verbosity may also help us out later when/if we add more complexity to algebraic types.

[TimWolla]

Note: This is not yet mentioned in UPGRADING / NEWS.