Improve variance implementation

This work is based off Nikita's review. Notably:

  - Implement contravariance in terms of covariance
  - Improve support for non-consecutive type decls
  - Adds _inheritance_status enum

Author: morrisonlevi

Zend/tests/bug76451.phpt

@@ -1,11 +1,5 @@
 --TEST--
-Aliases during inheritance type checks affected by opcache
---INI--
-opcache.enable=1
-opcache.enable_cli=1
-opcache.optimization_level=-1
---SKIPIF--
-<?php if (!extension_loaded('Zend OPcache') || php_sapi_name() != "cli") die("skip CLI only"); ?>
+Aliases during inheritance type checks (affected by opcache)
 --FILE--
 <?php
 require __DIR__ . "/bug76451.inc";

Zend/tests/type_declarations/nonconsecutive_variant_declarations_001.phpt

@@ -0,0 +1,20 @@
+--TEST--
+non-consecutive type decls are still checked for variance
+--FILE--
+<?php
+
+interface A {
+  function m(): A;
+}
+
+// "echo 'hi';" is not a declaration statement
+echo 'hi';
+
+class B implements A {
+  function m(): B { return $this; }
+}
+
+echo get_class((new B())->m());
+?>
+--EXPECT--
+hiB

Zend/tests/type_declarations/nonconsecutive_variant_declarations_002.phpt

@@ -0,0 +1,21 @@
+--TEST--
+non-consecutive type decls are still checked for variance
+--FILE--
+<?php
+
+interface A {
+  function m(): A;
+}
+
+// "echo 'hi';" is not a declaration statement
+echo 'hi';
+
+class B implements A {
+  function m(): stdClass { return $this; }
+}
+
+echo get_class((new B())->m());
+?>
+--EXPECTF--
+hi
+Fatal error: Declaration of B::m(): stdClass must be compatible with A::m(): A in %s on line %d

Zend/tests/typehints/undefined_type_during_variance_check_04.phpt

@@ -13,4 +13,3 @@ class Y implements X {
 ?>
 --EXPECTF--
 Fatal error: Declaration of Y::m(UndefinedA $z) must be compatible with X::m(stdClass $z) in %s on line %d
-

Zend/zend_compile.c

@@ -4086,7 +4086,6 @@ void zend_compile_static_call(znode *result, zend_ast *ast, uint32_t type) /* {{
 }
 /* }}} */
 
-
 static
 void _backup_unverified_variance_types(HashTable *unverified_types,
                                        HashTable **prev_unverified_types)
@@ -8091,8 +8090,9 @@ static zend_bool _is_not_decl_stmt(zend_ast *ast) {
 	if (ast) {
 		/* todo: what else should be considered a decl stmt? */
 		switch (ast->kind) {
-		case ZEND_AST_FUNC_DECL:
 		case ZEND_AST_CLASS:
+		case ZEND_AST_CONST_DECL:
+		case ZEND_AST_FUNC_DECL:
 			return 0;
 
 		default:
@@ -8120,11 +8120,10 @@ void zend_compile_top_stmt(zend_ast *ast) /* {{{ */
 	}
 
 	if (ast->kind == ZEND_AST_STMT_LIST) {
-		zend_ast_list *list = zend_ast_get_list(ast);
-		zend_ast **begin = list->child;
-		zend_ast **end = begin + list->children;
+		zend_ast_list *const list = zend_ast_get_list(ast);
+		zend_ast ** const begin = list->child;
+		zend_ast ** const end = begin + list->children;
 		zend_ast **first_decl = _ast_find(begin, end, &_is_type_decl);
-		zend_ast **last_decl = _ast_find(first_decl, end, &_is_not_decl_stmt);
 		zend_ast **p;
 
 		/* Compile opcodes before first type decl */
@@ -8133,7 +8132,8 @@ void zend_compile_top_stmt(zend_ast *ast) /* {{{ */
 		}
 
 		/* Compile decl stmts */
-		{
+		while (first_decl != end) {
+			zend_ast **last_decl = _ast_find(first_decl, end, &_is_not_decl_stmt);
 			HashTable unverified_types;
 			HashTable *prev_unverified_types;
 			_backup_unverified_variance_types(&unverified_types, &prev_unverified_types);
@@ -8146,12 +8146,14 @@ void zend_compile_top_stmt(zend_ast *ast) /* {{{ */
 
 			zend_hash_destroy(&unverified_types);
 			CG(unverified_types) = prev_unverified_types;
-		}
 
-		/* Compile remainder */
-		/* todo: loop to catch any non-consecutive type declarations */
-		for (p = last_decl; p < end; ++p) {
-			zend_compile_top_stmt(*p);
+			/* There can be non-consecutive type decls, so continue searching */
+			first_decl = _ast_find(last_decl, end, &_is_type_decl);
+
+			/* Compile any stmts between the two type decls (or the end) */
+			for (p = last_decl; p < first_decl; ++p) {
+				zend_compile_top_stmt(*p);
+			}
 		}
 		return;
 	}