toml: fix custom to_toml for complex structs (#19338)

vlib/toml/tests/encode_and_decode_test.v

@@ -121,6 +121,34 @@ title = 2'
 	assert y.title == .worker
 }
 
+struct Example1 {
+	arr []Problem
+}
+
+struct Example2 {
+	arr []Problem
+}
+
+struct Problem {
+	x int
+}
+
+pub fn (example Example1) to_toml() string {
+	return '[This is Valid]'
+}
+
+pub fn (problem Problem) to_toml() string {
+	return 'a problem'
+}
+
+fn test_custom_encode_of_complex_struct() {
+	assert toml.encode(Example1{}) == '[This is Valid]'
+	assert toml.encode(Example2{[Problem{}, Problem{}]}) == 'arr = [
+  "a problem",
+  "a problem"
+]'
+}
+
 fn test_array_encode_decode() {
 	a := Arrs{
 		strs: ['foo', 'bar']

vlib/toml/toml.v

@@ -101,7 +101,17 @@ fn encode_struct[T](typ T) map[string]Any {
 		} $else $if field.is_array {
 			mut arr := []Any{}
 			for v in value {
-				arr << Any(v)
+				$if v is Date {
+					arr << Any(v)
+				} $else $if v is Time {
+					arr << Any(v)
+				} $else $if v is DateTime {
+					arr << Any(v)
+				} $else $if v is $struct {
+					arr << Any(encode(v))
+				} $else {
+					arr << Any(v)
+				}
 			}
 			mp[field.name] = arr
 		} $else {