fix

vlib/v/checker/checker.v

@@ -5034,7 +5034,7 @@ fn (mut c Checker) ensure_generic_type_specify_type_names(typ ast.Type, pos toke
 		}
 		.sum_type {
 			info := sym.info as ast.SumType
-			if info.generic_types.len > 0 && !typ.has_flag(.generic) && info.concrete_types.len == 0 {
+			if info.generic_types.len > 0 && info.concrete_types.len == 0 {
 				c.error('`${sym.name}` type is generic sumtype, must specify the generic type names, e.g. ${sym.name}[T], ${sym.name}[int]',
 					pos)
 				return false

vlib/v/checker/tests/generics_field_struct_arr_err.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/generics_field_struct_arr_err.vv:20:6: error: `Callback` type is generic sumtype, must specify the generic type names, e.g. Callback[T], Callback[int]
+   18 |     v T
+   19 |     prev T
+   20 |     cb2 []Callback
+      |         ~~~~~~~~~~
+   21 |     a int 
+   22 | }

vlib/v/checker/tests/generics_field_struct_arr_err.vv

@@ -0,0 +1,24 @@
+// callback types
+type CBnoret[T] = fn (val T)
+
+type CBnoret2[T] = fn (val T, prev T)
+
+type CBvret[T] = fn (val T) T
+
+type CBvret2[T] = fn (val T, prev T) T
+
+type Callback[T] = CBnoret[T] | CBnoret2[T] | CBvret[T] | CBvret2[T]
+
+interface IObv[T] {
+	v    T
+	prev T
+	cb   []Callback[T]
+}
+
+struct Obv[T] {
+mut:
+	v    T
+	prev T
+	cb2  []Callback
+	a    int
+}

vlib/v/parser/parse_type.v

@@ -123,19 +123,6 @@ fn (mut p Parser) parse_array_type(expecting token.Kind, is_option bool) ast.Typ
 	idx := p.table.find_or_register_array_with_dims(elem_type, nr_dims)
 	if elem_type.has_flag(.generic) {
 		return ast.new_type(idx).set_flag(.generic)
-	} else {
-		sym := p.table.sym(elem_type)
-		match sym.info {
-			ast.Struct, ast.Interface, ast.SumType {
-				if sym.info.is_generic {
-					if p.tok.kind != .lsbr {
-						p.error_with_pos('`${sym.name}` type is generic type, must specify the generic type names, e.g. []${sym.name}[T]',
-							name_pos)
-					}
-				}
-			}
-			else {}
-		}
 	}
 	return ast.new_type(idx)
 }