Extract logging logic

Previously logging logic was scattered over OS class implementations
with plenty of duplication. Major changes in this commit:

 - Extracted logging logic into a separate Logger hierarchy. It allows
   easy configuration of logging mechanism depending on compile-time or
   run-time configuration.

 - Implemented RotatedFileLogger which is usually used with StdLogger,
   providing persistency of logs. It is often important to be able to
   obtain logs of the game even in production to be able to understand
   what happened prior to some problem. On mobile there previously was
   no way to obtain the logs aside from having the device connected to
   your machine.

 - flush() is not performed in release mode for every logged line. It
   is only performed for errors.

1 files changed, 18 insertions, 16 deletions

diff --git a/core/os/os.cpp b/core/os/os.cpp
index 437ce01a5e..ff17cdb508 100644
--- a/core/os/os.cpp
+++ b/core/os/os.cpp
@@ -62,20 +62,20 @@ void OS::debug_break(){
 	// something
 };
 
-void OS::print_error(const char *p_function, const char *p_file, int p_line, const char *p_code, const char *p_rationale, ErrorType p_type) {
-
-	const char *err_type = "**ERROR**";
-	switch (p_type) {
-		case ERR_ERROR: err_type = "**ERROR**"; break;
-		case ERR_WARNING: err_type = "**WARNING**"; break;
-		case ERR_SCRIPT: err_type = "**SCRIPT ERROR**"; break;
-		case ERR_SHADER: err_type = "**SHADER ERROR**"; break;
-		default: ERR_PRINT("Unknown error type"); break;
+void OS::_set_logger(Logger *p_logger) {
+	if (_logger) {
+		memdelete(_logger);
 	}
+	_logger = p_logger;
+}
+
+void OS::initialize_logger() {
+	_set_logger(memnew(StdLogger));
+}
+
+void OS::print_error(const char *p_function, const char *p_file, int p_line, const char *p_code, const char *p_rationale, Logger::ErrorType p_type) {
 
-	if (p_rationale && *p_rationale)
-		print("%s: %s\n ", err_type, p_rationale);
-	print("%s: At: %s:%i:%s() - %s\n", err_type, p_file, p_line, p_function, p_code);
+	_logger->log_error(p_function, p_file, p_line, p_code, p_rationale, p_type);
 }
 
 void OS::print(const char *p_format, ...) {
@@ -83,17 +83,16 @@ void OS::print(const char *p_format, ...) {
 	va_list argp;
 	va_start(argp, p_format);
 
-	vprint(p_format, argp);
+	_logger->logv(p_format, argp, false);
 
 	va_end(argp);
 };
 
 void OS::printerr(const char *p_format, ...) {
-
 	va_list argp;
 	va_start(argp, p_format);
 
-	vprint(p_format, argp, true);
+	_logger->logv(p_format, argp, true);
 
 	va_end(argp);
 };
@@ -533,9 +532,12 @@ OS::OS() {
 
 	_allow_hidpi = true;
 	_stack_bottom = (void *)(&stack_bottom);
+
+	_logger = NULL;
+	_set_logger(memnew(StdLogger));
 }
 
 OS::~OS() {
-
+	memdelete(_logger);
 	singleton = NULL;
 }