toml: implement decode method for Doc (#19318)

vlib/toml/tests/encode_and_decode_test.v

@@ -178,12 +178,50 @@ times = [
 	assert toml.decode[Arrs](s)! == a
 }
 
+fn test_decode_doc() {
+	doc := toml.parse_text('name = "Peter"
+age = 28
+is_human = true
+salary = 100000.5
+title = 2')!
+	e := doc.decode[Employee]()!
+	assert e.name == 'Peter'
+	assert e.age == 28
+	assert e.salary == 100000.5
+	assert e.is_human == true
+	assert e.title == .manager
+}
+
 fn test_unsupported_type() {
 	s := 'name = "Peter"'
 	err_msg := 'toml.decode: expected struct, found '
-	toml.decode[string](s) or { assert err.msg() == err_msg + 'string' }
-	toml.decode[[]string](s) or { assert err.msg() == err_msg + '[]string' }
-	toml.decode[int](s) or { assert err.msg() == err_msg + 'int' }
-	toml.decode[[]f32](s) or { assert err.msg() == err_msg + '[]f32' }
+	if _ := toml.decode[string](s) {
+		assert false
+	} else {
+		assert err.msg() == err_msg + 'string'
+	}
+	if _ := toml.decode[[]string](s) {
+		assert false
+	} else {
+		assert err.msg() == err_msg + '[]string'
+	}
+	if _ := toml.decode[int](s) {
+		assert false
+	} else {
+		assert err.msg() == err_msg + 'int'
+	}
+	if _ := toml.decode[[]f32](s) {
+		assert false
+	} else {
+		assert err.msg() == err_msg + '[]f32'
+	}
 	// ...
+
+	doc := toml.parse_text('name = "Peter"')!
+	assert doc.value('name').string() == 'Peter'
+	if _ := doc.decode[string]() {
+		assert false
+	} else {
+		assert err.msg() == 'Doc.decode: expected struct, found string'
+	}
 }

vlib/toml/toml.v

@@ -252,6 +252,16 @@ fn parse_array_key(key string) (string, int) {
 	return k, index
 }
 
+// decode decodes a TOML `string` into the target struct type `T`.
+pub fn (d Doc) decode[T]() !T {
+	$if T !is $struct {
+		return error('Doc.decode: expected struct, found ${T.name}')
+	}
+	mut typ := T{}
+	decode_struct(d.to_any(), mut typ)
+	return typ
+}
+
 // to_any converts the `Doc` to toml.Any type.
 pub fn (d Doc) to_any() Any {
 	return ast_to_any(d.ast.table)