toml: easier scanner configuration (#12016)

vlib/toml/input/input.v

@@ -3,6 +3,8 @@
 // that can be found in the LICENSE file.
 module input
 
+import os
+
 // Config is used to configure input to the toml module.
 // Only one of the fields `text` and `file_path` is allowed to be set at time of configuration.
 pub struct Config {
@@ -11,6 +13,23 @@ pub:
 	file_path string // '/path/to/file.toml'
 }
 
+// auto_config returns an, automatic determined, input Config based on heuristics
+// found in `toml`
+pub fn auto_config(toml string) ?Config {
+	mut config := Config{}
+	if !toml.contains('\n') && os.is_file(toml) {
+		config = Config{
+			file_path: toml
+		}
+	} else {
+		config = Config{
+			text: toml
+		}
+	}
+	config.validate() ?
+	return config
+}
+
 // validate returns an optional error if more than one of the fields
 // in `Config` has a non-default value (empty string).
 pub fn (c Config) validate() ? {
@@ -22,3 +41,14 @@ pub fn (c Config) validate() ? {
 			' ${typeof(c).name} must either contain a valid `file_path` OR a non-empty `text` field')
 	}
 }
+
+pub fn (c Config) read_input() ?string {
+	mut text := c.text
+	if os.is_file(c.file_path) {
+		text = os.read_file(c.file_path) or {
+			return error(@MOD + '.' + @STRUCT + '.' + @FN +
+				' Could not read "$c.file_path": "$err.msg"')
+		}
+	}
+	return text
+}