Improve user-friendliness of the validation options

* Fixes #4223, by making the --validate and --validate-* options imply --nocache.

* Fixes #4224, showing an error if you misspell the id argument to
  --validate-addon. The application doesn't (but should) quit automatically to
  avoid the user spending time on a non-functional validation run, however it
  does at least disable all add-ons, which should have the same end result.

* Shows a warning that --validate-addon needs the user to play the add-on, it
  doesn't automatically check the add-on. This was my misunderstanding when
  logging issue #4225, which has now been repurposed into a feature request for
  a new tool that does what I thought --validate-addon did.

src/commandline_options.cpp

@@ -287,7 +287,7 @@ commandline_options::commandline_options (const std::vector<std::string>& args)
 	parsing_opts.add_options()
 		("use-schema,S", po::value<std::string>(), "specify a schema to validate WML against (defaults to the core schema)")
 		("validate,V", po::value<std::string>(), "validate a specified WML file against a schema")
-		("validate-addon", po::value<std::string>(), "validate the specified addon's WML against the schema")
+		("validate-addon", po::value<std::string>(), "validate the specified addon's WML against the schema. Requires the user to play the campaign (in the GUI) to trigger the validation.")
 		("validate-core", "validate the core WML against the schema")
 		("validate-schema", po::value<std::string>(), "validate a specified WML schema")
 		("diff,D", po::value<two_strings>()->multitoken(), "diff two preprocessed WML documents")
@@ -516,6 +516,7 @@ commandline_options::commandline_options (const std::vector<std::string>& args)
 		userdata_path = true;
 	if (vm.count("validcache"))
 		validcache = true;
+	// If you add a new validate-* option, remember the any_validation_option() function
 	if (vm.count("validate"))
 		validate_wml = vm["validate"].as<std::string>();
 	if (vm.count("validate-core"))
@@ -524,6 +525,7 @@ commandline_options::commandline_options (const std::vector<std::string>& args)
 		validate_addon = vm["validate-addon"].as<std::string>();
 	if (vm.count("validate-schema"))
 		validate_schema = vm["validate-schema"].as<std::string>();
+	// If you add a new validate-* option, remember the any_validation_option() function
 	if (vm.count("use-schema"))
 		validate_with = vm["use-schema"].as<std::string>();;
 	if (vm.count("version"))
@@ -650,3 +652,8 @@ config commandline_options::to_config() const {
 	}
 	return ret;
 }
+
+bool commandline_options::any_validation_option() const
+{
+	return validate_addon || validate_core || validate_schema || validate_with || validate_wml;
+}

src/commandline_options.hpp

@@ -46,6 +46,9 @@ friend std::ostream& operator<<(std::ostream &os, const commandline_options& cmd
 
 	config to_config() const; /* Used by lua scrips. Not all of the options need to be exposed here, just those exposed to lua */
 
+	/// True if the --validate or any of the --validate-*  options are given.
+	bool any_validation_option() const;
+
 	/// Non-empty if --bunzip2 was given on the command line. Uncompresses a .bz2 file and exits.
 	boost::optional<std::string> bunzip2;
 	/// Non-empty if --bzip2 was given on the command line. Compresses a file to .bz2 and exits.

src/game_config_manager.cpp

@@ -62,7 +62,9 @@ game_config_manager::game_config_manager(
 	assert(!singleton);
 	singleton = this;
 
-	if(cmdline_opts_.nocache) {
+	// All of the validation options imply --nocache, as the validation happens during cache
+	// rebuilding. If the cache isn't rebuilt, validation is silently skipped.
+	if(cmdline_opts_.nocache || cmdline_opts_.any_validation_option()) {
 		cache_.set_use_cache(false);
 	}
 	if(cmdline_opts_.validcache) {
@@ -565,6 +567,18 @@ void game_config_manager::load_addons_cfg()
 		}
 	}
 
+	if(cmdline_opts_.validate_addon) {
+		if(!addon_cfgs_.count(*cmdline_opts_.validate_addon)) {
+			ERR_CONFIG << "Didn’t find an add-on for --validate-addon - check whether the id has a typo" << std::endl;
+			const std::string log_msg = formatter()
+				<< "Didn't find an add-on for --validate-addon - check whether the id has a typo";
+			error_log.push_back(log_msg);
+			throw game::error("Did not find an add-on for --validate-addon");
+		}
+
+		WRN_CONFIG << "Note: for --validate-addon to find errors, you have to play (in the GUI) a game that uses the add-on.";
+	}
+
 	if(!error_addons.empty()) {
 		const std::size_t n = error_addons.size();
 		const std::string& msg1 =