config/File: print warning about deprecated options

src/config/File.cxx

@@ -116,6 +116,11 @@ ReadConfigBlock(ConfigData &config_data, BufferedReader &reader,
 	const unsigned i = unsigned(o);
 	const ConfigTemplate &option = config_block_templates[i];
 
+	if (option.deprecated)
+		FormatWarning(config_file_domain,
+			      "config parameter \"%s\" on line %u is deprecated",
+			      name, reader.GetLineNumber());
+
 	if (!option.repeatable)
 		if (const auto *block = config_data.GetBlock(o))
 			throw FormatRuntimeError("config parameter \"%s\" is first defined "
@@ -143,6 +148,11 @@ ReadConfigParam(ConfigData &config_data, BufferedReader &reader,
 	const unsigned i = unsigned(o);
 	const ConfigTemplate &option = config_param_templates[i];
 
+	if (option.deprecated)
+		FormatWarning(config_file_domain,
+			      "config parameter \"%s\" on line %u is deprecated",
+			      name, reader.GetLineNumber());
+
 	if (!option.repeatable)
 		if (const auto *param = config_data.GetParam(o))
 			throw FormatRuntimeError("config parameter \"%s\" is first defined "

src/config/Templates.hxx

@@ -24,7 +24,6 @@ struct ConfigTemplate {
 	const char *const name;
 	const bool repeatable;
 
-	// TODO: print warning when a deprecated option is used
 	const bool deprecated;
 
 	constexpr ConfigTemplate(const char *_name,