toml: fix toml encoding of complex types (#19408)

* Improve default toml encoder for complex types

The default toml encoder failed for more complex structs, as certain
edge cases were not covered. This commit attempts to fix this by adding
additional handling for these edge cases.

* Improve map encoding

Since maps currently only support keys that have a string
representation, we can utilize this during map encoding.

* Add test cases for toml encoding

Added test cases for toml encoding of complex nested structs and structs
that contain maps.

* Add additional test cases

vlib/toml/tests/encode_and_decode_test.v

@@ -149,6 +149,47 @@ fn test_custom_encode_of_complex_struct() {
 ]'
 }
 
+struct Example3 {
+	arr_arr [][]Problem
+}
+
+struct Example4 {
+	mp map[string]Problem
+}
+
+pub fn (example Example3) to_toml() string {
+	return '[This is Valid]'
+}
+
+pub fn (example Example4) to_toml() string {
+	return '[This is Valid]'
+}
+
+fn test_custom_encode_of_nested_complex_struct() {
+	assert toml.encode(Example3{}) == '[This is Valid]'
+	assert toml.encode(Example4{}) == '[This is Valid]'
+}
+
+struct Example5 {
+	mp map[string]Problem
+}
+
+fn test_map_encode_of_complex_struct() {
+	mut mp := map[string]Problem{}
+	mp['key_one'] = Problem{}
+	mp['key_two'] = Problem{}
+	assert toml.encode(Example5{ mp: mp }) == 'mp = { key_one = "a problem", key_two = "a problem" }'
+}
+
+struct Example6 {
+	ptr voidptr
+	r   rune
+}
+
+fn test_encode_for_exotic_types() {
+	assert toml.encode(Example6{ ptr: &voidptr(0), r: `🚀` }) == 'ptr = "0x0"\nr = "🚀"'
+}
+
 fn test_array_encode_decode() {
 	a := Arrs{
 		strs: ['foo', 'bar']

vlib/toml/toml.v

@@ -93,32 +93,54 @@ pub fn encode[T](typ T) string {
 fn encode_struct[T](typ T) map[string]Any {
 	mut mp := map[string]Any{}
 	$for field in T.fields {
-		value := typ.$(field.name)
-		$if field.is_enum {
-			mp[field.name] = Any(int(value))
-		} $else $if field.is_struct {
-			mp[field.name] = encode_struct(value)
-		} $else $if field.is_array {
-			mut arr := []Any{}
-			for v in value {
-				$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))
-				} $else {
-					arr << Any(v)
-				}
+		mp[field.name] = to_any(typ.$(field.name))
+	}
+	return mp
+}
+
+fn to_any[T](value T) Any {
+	$if T is $enum {
+		return Any(int(value))
+	} $else $if T is Date {
+		return Any(value)
+	} $else $if T is Time {
+		return Any(value)
+	} $else $if T is Null {
+		return Any(value)
+	} $else $if T is bool {
+		return Any(value)
+	} $else $if T is $float {
+		return Any(value)
+	} $else $if T is i64 {
+		return Any(value)
+	} $else $if T is int {
+		return Any(value)
+	} $else $if T is u64 {
+		return Any(value)
+	} $else $if T is DateTime {
+		return Any(value)
+	} $else $if T is $struct {
+		$for method in T.methods {
+			$if method.name == 'to_toml' {
+				return Any(value.$method())
 			}
-			mp[field.name] = arr
-		} $else {
-			mp[field.name] = Any(value)
 		}
+		return encode_struct(value)
+	} $else $if T is $array {
+		mut arr := []Any{cap: value.len}
+		for v in value {
+			arr << to_any(v)
+		}
+		return arr
+	} $else $if T is $map {
+		mut mmap := map[string]Any{}
+		for key, val in value {
+			mmap['${key}'] = to_any(val)
+		}
+		return mmap
+	} $else {
+		return Any('${value}')
 	}
-	return mp
 }
 
 // DateTime is the representation of an RFC 3339 datetime string.