OS: Better validation of invalid input for get_unix_time_from_datetime

Default missing keys to Unix time 0 (1970-01-01 at 00:00:00 UTC).
Abort if year <= 0, this is not supported by the current algorithm.

Prevents an infinite loop further down.

Fixes #49022.

(cherry picked from commit 62efa30ed239b89538730a9528e10af50cdce1a1)

core/bind/core_bind.cpp

@@ -760,7 +760,7 @@ int64_t _OS::get_unix_time_from_datetime(Dictionary datetime) const {
 	unsigned int hour = ((datetime.has(HOUR_KEY)) ? static_cast<unsigned int>(datetime[HOUR_KEY]) : 0);
 	unsigned int day = ((datetime.has(DAY_KEY)) ? static_cast<unsigned int>(datetime[DAY_KEY]) : 1);
 	unsigned int month = ((datetime.has(MONTH_KEY)) ? static_cast<unsigned int>(datetime[MONTH_KEY]) : 1);
-	unsigned int year = ((datetime.has(YEAR_KEY)) ? static_cast<unsigned int>(datetime[YEAR_KEY]) : 0);
+	unsigned int year = ((datetime.has(YEAR_KEY)) ? static_cast<unsigned int>(datetime[YEAR_KEY]) : 1970);
 
 	/// How many days come before each month (0-12)
 	static const unsigned short int DAYS_PAST_THIS_YEAR_TABLE[2][13] = {
@@ -771,15 +771,14 @@ int64_t _OS::get_unix_time_from_datetime(Dictionary datetime) const {
 	};
 
 	ERR_FAIL_COND_V_MSG(second > 59, 0, "Invalid second value of: " + itos(second) + ".");
-
 	ERR_FAIL_COND_V_MSG(minute > 59, 0, "Invalid minute value of: " + itos(minute) + ".");
-
 	ERR_FAIL_COND_V_MSG(hour > 23, 0, "Invalid hour value of: " + itos(hour) + ".");
-
+	ERR_FAIL_COND_V_MSG(year == 0, 0, "Years before 1 AD are not supported. Value passed: " + itos(year) + ".");
 	ERR_FAIL_COND_V_MSG(month > 12 || month == 0, 0, "Invalid month value of: " + itos(month) + ".");
-
 	// Do this check after month is tested as valid
-	ERR_FAIL_COND_V_MSG(day > MONTH_DAYS_TABLE[LEAPYEAR(year)][month - 1] || day == 0, 0, "Invalid day value of '" + itos(day) + "' which is larger than '" + itos(MONTH_DAYS_TABLE[LEAPYEAR(year)][month - 1]) + "' or 0.");
+	unsigned int days_in_month = MONTH_DAYS_TABLE[LEAPYEAR(year)][month - 1];
+	ERR_FAIL_COND_V_MSG(day == 0 || day > days_in_month, 0, "Invalid day value of: " + itos(day) + ". It should be comprised between 1 and " + itos(days_in_month) + " for month " + itos(month) + ".");
+
 	// Calculate all the seconds from months past in this year
 	uint64_t SECONDS_FROM_MONTHS_PAST_THIS_YEAR = DAYS_PAST_THIS_YEAR_TABLE[LEAPYEAR(year)][month - 1] * SECONDS_PER_DAY;
 

doc/classes/OS.xml

@@ -550,7 +550,7 @@
 			<description>
 				Gets an epoch time value from a dictionary of time values.
 				[code]datetime[/code] must be populated with the following keys: [code]year[/code], [code]month[/code], [code]day[/code], [code]hour[/code], [code]minute[/code], [code]second[/code].
-				If the dictionary is empty [code]0[/code] is returned.
+				If the dictionary is empty [code]0[/code] is returned. If some keys are omitted, they default to the equivalent values for the UNIX epoch timestamp 0 (1970-01-01 at 00:00:00 UTC).
 				You can pass the output from [method get_datetime_from_unix_time] directly into this function. Daylight Savings Time ([code]dst[/code]), if present, is ignored.
 			</description>
 		</method>