checker: fix struct field init with generic fn variable (fix #20847) (#20878)

Author: yuyi98

vlib/v/checker/assign.v

@@ -189,8 +189,8 @@ fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 		if is_decl || is_shared_re_assign {
 			// check generic struct init and return unwrap generic struct type
 			if mut right is ast.StructInit {
+				c.expr(mut right)
 				if right.typ.has_flag(.generic) {
-					c.expr(mut right)
 					right_type = right.typ
 				}
 			} else if mut right is ast.PrefixExpr {

vlib/v/tests/struct_field_init_with_generic_fn_test.v

@@ -0,0 +1,25 @@
+struct ClassInfo {
+	func fn () = unsafe { nil }
+}
+
+pub fn func2[T]() {
+}
+
+pub fn func1[T]() {
+	ci := ClassInfo{
+		func: func2[T]
+	}
+	ci.func()
+}
+
+struct Struct1 {}
+
+struct Struct2 {}
+
+fn test_struct_field_init_with_generic_fn() {
+	func1[i32]()
+	func1[bool]()
+	func1[Struct1]()
+	func1[Struct2]()
+	assert true
+}