Revisions: Clarify lookup logic

find() now always returns revisions from the same change.  It is no
longer necessary to look at Change.Id in this condition.  In fact the
prior commit fixed a hidden bug this loop couldn't identify caused by
the RevisionResource having the wrong PatchSet associated to the
current Change. Pushing the filter logic down inside of match helps
to eliminate this bug.

The legacy PatchSet.Id syntax is verbose and easier to read when moved
into its own method.

The database scans on patchSets by revision id will need to change
as the database moves to notedb. Push these into their own helpers
that more easily clarify the two conditions being tested.

Inline the singleton toResources method, it's small and its name
was misleading converting a single PatchSet into a "resources".
The plural could mislead readers.

Change-Id: I1bb71a513b9e75aec10d6184d75105dd1a03c167

gerrit-server/src/main/java/com/google/gerrit/server/change/Revisions.java

@@ -33,6 +33,7 @@ import com.google.gerrit.reviewdb.server.ReviewDb;
 import com.google.gerrit.server.edit.ChangeEdit;
 import com.google.gerrit.server.edit.ChangeEditUtil;
 import com.google.gwtorm.server.OrmException;
+import com.google.gwtorm.server.ResultSet;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 import com.google.inject.Singleton;
@@ -77,11 +78,10 @@ public class Revisions implements ChildCollection<ChangeResource, RevisionResour
       }
       throw new ResourceNotFoundException(id);
     }
+
     List<RevisionResource> match = Lists.newArrayListWithExpectedSize(2);
     for (RevisionResource rsrc : find(change, id.get())) {
-      Change.Id changeId = rsrc.getChange().getId();
-      if (changeId.equals(change.getChange().getId())
-          && visible(change, rsrc.getPatchSet())) {
+      if (visible(change, rsrc.getPatchSet())) {
         match.add(rsrc);
       }
     }
@@ -104,19 +104,11 @@ public class Revisions implements ChildCollection<ChangeResource, RevisionResour
 
   private List<RevisionResource> find(ChangeResource change, String id)
       throws OrmException {
-    ReviewDb db = dbProvider.get();
-
     if (id.equals("0")) {
       return loadEdit(change, null);
     } else if (id.length() < 6 && id.matches("^[1-9][0-9]{0,4}$")) {
       // Legacy patch set number syntax.
-      PatchSet ps = dbProvider.get().patchSets().get(new PatchSet.Id(
-          change.getChange().getId(),
-          Integer.parseInt(id)));
-      if (ps != null) {
-        return toResources(change, ps);
-      }
-      return Collections.emptyList();
+      return byLegacyPatchSetId(change, id);
     } else if (id.length() < 4 || id.length() > RevId.LEN) {
       // Require a minimum of 4 digits.
       // Impossibly long identifier will never match.
@@ -128,20 +120,15 @@ public class Revisions implements ChildCollection<ChangeResource, RevisionResour
       // for all patch sets in the change.
       RevId revid = new RevId(id);
       if (revid.isComplete()) {
-        List<RevisionResource> list =
-            toResources(change, db.patchSets().byRevision(revid));
-        if (list.isEmpty()) {
-          return loadEdit(change, revid);
-        }
-        return list;
-      } else {
-        return toResources(
-            change, db.patchSets().byRevisionRange(revid, revid.max()));
+        List<RevisionResource> m = toResources(change, findExactMatch(revid));
+        return m.isEmpty() ? loadEdit(change, revid)  : m;
       }
+      return toResources(change, findByPrefix(revid));
     } else {
       // Chance of collision rises; look at all patch sets on the change.
       List<RevisionResource> out = Lists.newArrayList();
-      for (PatchSet ps : db.patchSets().byChange(change.getChange().getId())) {
+      for (PatchSet ps : dbProvider.get().patchSets()
+          .byChange(change.getChange().getId())) {
         if (ps.getRevision() != null && ps.getRevision().get().startsWith(id)) {
           out.add(new RevisionResource(change, ps));
         }
@@ -150,6 +137,25 @@ public class Revisions implements ChildCollection<ChangeResource, RevisionResour
     }
   }
 
+  private List<RevisionResource> byLegacyPatchSetId(ChangeResource change,
+      String id) throws OrmException {
+    PatchSet ps = dbProvider.get().patchSets().get(new PatchSet.Id(
+        change.getChange().getId(),
+        Integer.parseInt(id)));
+    if (ps != null) {
+      return Collections.singletonList(new RevisionResource(change, ps));
+    }
+    return Collections.emptyList();
+  }
+
+  private ResultSet<PatchSet> findExactMatch(RevId revid) throws OrmException {
+    return dbProvider.get().patchSets().byRevision(revid);
+  }
+
+  private ResultSet<PatchSet> findByPrefix(RevId revid) throws OrmException {
+    return dbProvider.get().patchSets().byRevisionRange(revid, revid.max());
+  }
+
   private List<RevisionResource> loadEdit(ChangeResource change, RevId revid)
       throws OrmException {
     try {
@@ -163,10 +169,10 @@ public class Revisions implements ChildCollection<ChangeResource, RevisionResour
               new RevisionResource(change, ps, edit));
         }
       }
+      return Collections.emptyList();
     } catch (AuthException | IOException e) {
       throw new OrmException(e);
     }
-    return Collections.emptyList();
   }
 
   private static List<RevisionResource> toResources(final ChangeResource change,
@@ -185,9 +191,4 @@ public class Revisions implements ChildCollection<ChangeResource, RevisionResour
           }
         }).toList();
   }
-
-  private static List<RevisionResource> toResources(ChangeResource change,
-      PatchSet ps) {
-    return Collections.singletonList(new RevisionResource(change, ps));
-  }
 }