checker: add error for struct fields of type []unknown

vlib/v/checker/checker.v

@@ -264,6 +264,13 @@ pub fn (mut c Checker) struct_decl(decl ast.StructDecl) {
 		if sym.kind == .placeholder && decl.language != .c && !sym.name.starts_with('C.') {
 			c.error('unknown type `$sym.name`', field.pos)
 		}
+		if sym.kind == .array {
+			array_info := sym.array_info()
+			elem_sym := c.table.get_type_symbol(array_info.elem_type)
+			if elem_sym.kind == .placeholder {
+				c.error('unknown type `$elem_sym.name`', field.pos)
+			}
+		}
 		if sym.kind == .struct_ {
 			info := sym.info as table.Struct
 			if info.is_ref_only && !field.typ.is_ptr() {

vlib/v/checker/tests/unknown_array_element_type_a.out

@@ -1,4 +1,4 @@
-vlib/v/checker/tests/unknown_array_element_type.v:2:9: error: unknown type `abc`
+vlib/v/checker/tests/unknown_array_element_type_a.v:2:9: error: unknown type `abc`
     1 | fn main() {
     2 |     a := []abc{}
       |            ~~~

vlib/v/checker/tests/unknown_array_element_type_b.out

@@ -0,0 +1,6 @@
+vlib/v/checker/tests/unknown_array_element_type_b.v:2:2: error: unknown type `abc`
+    1 | struct Aaa {
+    2 |     a []abc
+      |     ~~~~~~~
+    3 | }
+    4 |

vlib/v/checker/tests/unknown_array_element_type_b.vv

@@ -0,0 +1,9 @@
+struct Aaa {
+	a []abc
+}
+
+fn main() {
+	s := Aaa{}
+	println(s)
+}
+

vlib/v/parser/struct.v

@@ -105,9 +105,9 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 			}
 			field_start_pos := p.tok.position()
 			field_name := p.check_name()
-			field_pos := field_start_pos.extend(p.tok.position())
 			// p.warn('field $field_name')
 			typ := p.parse_type()
+			field_pos := field_start_pos.extend(p.tok.position())
 			/*
 			if name == '_net_module_s' {
 			s := p.table.get_type_symbol(typ)