Make snapshot-lsif command more LSIF-compliant

Previously, the snapshot command assumed that monikers had an incoming
edge from a result set. However, LSIF allows the moniker edge to come
from the range vertex, and it also permits recursive result sets. This
commit updates the snapshot command so that it computes monikers
according to the spec.

Author: olafurpg

lsif-java/src/main/scala/com/sourcegraph/lsif_java/commands/SnapshotLsifCommand.scala

@@ -114,16 +114,11 @@ object SnapshotLsifCommand {
           else
             Role.REFERENCE
 
-        val symbol =
-          (
-            for {
-              resultSetId <- lsif.next.get(o.getId)
-              monikerId <- lsif.moniker.get(resultSetId)
-              moniker <- lsif.monikerIdentifier.get(monikerId)
-            } yield moniker
-          ).getOrElse {
+        val symbol = lsif
+          .symbolFromRange(o)
+          .getOrElse {
             val id = lsif.next.getOrElse(o.getId, o.getId)
-            s"local$id"
+            s"missingMoniker$id"
           }
         val occ = SymbolOccurrence
           .newBuilder()
@@ -189,6 +184,20 @@ object SnapshotLsifCommand {
     def textDocument(id: Int): TextDocument.Builder = {
       documents.getOrElseUpdate(id, TextDocument.newBuilder())
     }
+    def symbolFromRange(o: LsifObject): Option[String] = {
+      val moniker =
+        for {
+          monikerId <- this.moniker.get(o.getId())
+          moniker <- this.monikerIdentifier.get(monikerId)
+        } yield moniker
+      moniker.orElse {
+        for {
+          resultSetId <- this.next.get(o.getId())
+          resultSet <- this.byId.get(resultSetId)
+          fromResultSet <- symbolFromRange(resultSet)
+        } yield fromResultSet
+      }
+    }
 
     val monikers: Map[String, LsifObject] =
       objects