METAR parsing: parse more cloud covers

Parse cloud coverage with no coverage or height
SF-ID: https://sourceforge.net/p/flightgear/codetickets/2750/

simgear/environment/metar.cxx

@@ -123,7 +123,7 @@ SGMetar::SGMetar(const string& m) :
 	while (scanVisibility()) ;
 	while (scanRwyVisRange()) ;
 	while (scanWeather()) ;
-	while (scanSkyCondition()) ;
+	while (scanSkyCondition()) { }
 
     if (!scanTemperature()) {
         throw sg_io_exception("metar temperature data malformed or missing ", sg_location(_url));
@@ -1048,12 +1048,12 @@ bool SGMetar::scanSkyCondition()
 	SGMetarCloud cl;
 
 	if (!strncmp(m, "//////", 6)) {
-		m += 6;
-		if (!scanBoundary(&m))
-			return false;
-		_m = m;
+		char* m2 = m+6;
+		if (scanBoundary(&m2)) {
+			_m = m2;
 			return true;
 		}
+	}
 
 	if (!strncmp(m, "CLR", i = 3)				// clear
 			|| !strncmp(m, "SKC", i = 3)		// sky clear
@@ -1074,9 +1074,10 @@ bool SGMetar::scanSkyCondition()
 		return true;
 	}
 
-	if (!strncmp(m, "VV", i = 2))				// vertical visibility
-		;
-	else if (!strncmp(m, "FEW", i = 3))
+	bool verticalVisibility = false;
+	if (!strncmp(m, "VV", i = 2)) {				// vertical visibility
+		verticalVisibility = true;
+	} else if (!strncmp(m, "FEW", i = 3))
         cl._coverage = SGMetarCloud::COVERAGE_FEW;
 	else if (!strncmp(m, "SCT", i = 3))
         cl._coverage = SGMetarCloud::COVERAGE_SCATTERED;
@@ -1084,6 +1085,8 @@ bool SGMetar::scanSkyCondition()
         cl._coverage = SGMetarCloud::COVERAGE_BROKEN;
 	else if (!strncmp(m, "OVC", i = 3))
         cl._coverage = SGMetarCloud::COVERAGE_OVERCAST;
+	else if (!strncmp(m, "///", i = 3))
+		cl._coverage = SGMetarCloud::COVERAGE_NIL; // should we add 'unknown'?
 	else
 		return false;
 	m += i;
@@ -1099,7 +1102,7 @@ bool SGMetar::scanSkyCondition()
 	} else if (!scanNumber(&m, &i, 3))
 		i = -1;
 
-	if (cl._coverage == SGMetarCloud::COVERAGE_NIL) {
+	if (verticalVisibility) {
 		 if (!scanBoundary(&m))
 		 	return false;
 		if (i == -1)			// 'VV///'

simgear/environment/test_metar.cxx

@@ -106,6 +106,29 @@ void test_wind_unit_not_specified()
     SG_CHECK_EQUAL_EP2(m1.getGustSpeed_kt(), 14.0, TEST_EPSILON);
 }
 
+void test_clouds_without_height()
+{
+    // apparently EGPF has a faulty automated cloud sensor? :)
+    SGMetar m1("EGPF 111420Z AUTO 24013KT 9000 -RA SCT019/// BKN023/// BKN030/// //////TCU 13/11 Q1011 RERA");
+}
+
+void test_GLRB_failure()
+{
+    // Haze entered backwards, genuinely invalid
+#if 0
+    SGMetar m1("2022/04/04 11:00 GLRB 041100Z 29012KT 8000 HZVC NSC 29/21 Q1012 NOSIG");
+#endif
+}
+
+void test_LOWK_failure()
+{
+    // surface winds specification won't parse, looks invalid 
+#if 0
+    SGMetar m3("LOWK 051526Z AUTO 217G33KT 10SM VCTS FEW017 BKN023 OVC041 23/21 A2970 "
+    "RMK AO2 PK WND 21037/1458 LTG DSNT ALQDS RAE09 P0000 T02330206");
+#endif
+}
+
 int main(int argc, char* argv[])
 {
     try {
@@ -115,6 +138,9 @@ int main(int argc, char* argv[])
         test_sensor_failure_wind();
         test_wind_unit_not_specified();
         test_drizzle();
+        test_clouds_without_height();
+        test_GLRB_failure();
+        test_LOWK_failure();
     } catch (sg_exception& e) {
         cerr << "got exception:" << e.getMessage() << endl;
         return -1;