Add a consistency query

java/ql/consistency-queries/locations.ql

@@ -0,0 +1,21 @@
+import java
+
+// Locations should either be :0:0:0:0 locations (UnknownLocation, or
+// a whole file), or all 4 fields should be positive.
+Location badLocation() {
+  [result.getStartLine(), result.getEndLine(), result.getStartColumn(), result.getEndColumn()] != 0 and
+  [result.getStartLine(), result.getEndLine(), result.getStartColumn(), result.getEndColumn()] < 1
+}
+
+// The start should not be after the end.
+Location backwardsLocation() {
+  result.getStartLine() > result.getEndLine()
+  or
+  result.getStartLine() = result.getEndLine() and
+  result.getStartColumn() > result.getEndColumn()
+}
+
+from Location l
+where l = badLocation() or l = backwardsLocation()
+select l
+