Change the return type of ChangeNotes.getChangeMessages()

Changed ChangeNotes so that ChangeNotes.getChangeMessages()
returns a mapping of PatchSet IDs to ChangeMessages instead
of Strings. This allows us to keep the metadata about each
ChangeMessage (i.e. the related patchset, timestamp,
etc).

To construct ChangeMessages, we used the SHA-1 of the
commit in the notedb graph as the uuid for the Key. We
needed that unique identifier for the ChangeMessage because
it's documented in the REST API, but its format wasn't
documented, so it didn't need to be a UUID. The SHA-1 of the
commit should be unique enough.  Note that IDs of existing
messages will change after converting a site to notedb. This
should be fine though because no API actually reads the UUID
field (either the external REST API or anything internal in
Gerrit).

Change-Id: I55a16419cfd73cecf21d97c5a4040f5b6932df32

gerrit-server/src/test/java/com/google/gerrit/server/notedb/ChangeNotesTest.java

@@ -32,6 +32,7 @@ import com.google.gerrit.common.data.SubmitRecord;
 import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.Branch;
 import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.ChangeMessage;
 import com.google.gerrit.reviewdb.client.PatchSet;
 import com.google.gerrit.reviewdb.client.PatchSetApproval;
 import com.google.gerrit.reviewdb.client.PatchSetInfo;
@@ -640,11 +641,19 @@ public class ChangeNotesTest {
     update.putReviewer(changeOwner.getAccount().getId(), REVIEWER);
     update.setChangeMessage("Just a little code change.\n");
     update.commit();
+    PatchSet.Id ps1 = c.currentPatchSetId();
 
     ChangeNotes notes = newNotes(c);
-    List<String> changeMessages = notes.getChangeMessages();
-    assertEquals(1, changeMessages.size());
-    assertEquals("Just a little code change.\n", changeMessages.get(0));
+    ListMultimap<PatchSet.Id, ChangeMessage> changeMessages =
+        notes.getChangeMessages();
+    assertEquals(1, changeMessages.keySet().size());
+
+    ChangeMessage cm = Iterables.getOnlyElement(changeMessages.get(ps1));
+    assertEquals("Just a little code change.\n",
+        cm.getMessage());
+    assertEquals(changeOwner.getAccount().getId(),
+        cm.getAuthor());
+    assertEquals(ps1, cm.getPatchSetId());
   }
 
   @Test
@@ -664,10 +673,22 @@ public class ChangeNotesTest {
     PatchSet.Id ps2 = c.currentPatchSetId();
 
     ChangeNotes notes = newNotes(c);
-    List<String> changeMessages = notes.getChangeMessages();
-    assertEquals(2, changeMessages.size());
-    assertEquals("This is the change message for the second PS.", changeMessages.get(0));
-    assertEquals("This is the change message for the first PS.", changeMessages.get(1));
+    ListMultimap<PatchSet.Id, ChangeMessage> changeMessages =
+        notes.getChangeMessages();
+    assertEquals(2, changeMessages.keySet().size());
+
+    ChangeMessage cm1 = Iterables.getOnlyElement(changeMessages.get(ps1));
+    assertEquals("This is the change message for the first PS.",
+        cm1.getMessage());
+    assertEquals(changeOwner.getAccount().getId(),
+        cm1.getAuthor());
+
+    ChangeMessage cm2 = Iterables.getOnlyElement(changeMessages.get(ps2));
+    assertEquals(ps1, cm1.getPatchSetId());
+    assertEquals("This is the change message for the second PS.",
+        cm2.getMessage());
+    assertEquals(changeOwner.getAccount().getId(), cm2.getAuthor());
+    assertEquals(ps2, cm2.getPatchSetId());
   }
 
   @Test
@@ -691,8 +712,9 @@ public class ChangeNotesTest {
     }
 
     ChangeNotes notes = newNotes(c);
-    List<String> changeMessages = notes.getChangeMessages();
-    assertEquals(0, changeMessages.size());
+    ListMultimap<PatchSet.Id, ChangeMessage> changeMessages =
+        notes.getChangeMessages();
+    assertEquals(0, changeMessages.keySet().size());
   }
 
   @Test
@@ -702,6 +724,7 @@ public class ChangeNotesTest {
     update.setChangeMessage("Testing trailing double newline\n"
         + "\n");
     update.commit();
+    PatchSet.Id ps1 = c.currentPatchSetId();
 
     RevWalk walk = new RevWalk(repo);
     try {
@@ -720,10 +743,14 @@ public class ChangeNotesTest {
     }
 
     ChangeNotes notes = newNotes(c);
-    List<String> changeMessages = notes.getChangeMessages();
-    assertEquals(1, changeMessages.size());
-    assertEquals("Testing trailing double newline\n"
-        + "\n", changeMessages.get(0));
+    ListMultimap<PatchSet.Id, ChangeMessage> changeMessages =
+        notes.getChangeMessages();
+    assertEquals(1, changeMessages.keySet().size());
+
+    ChangeMessage cm1 = Iterables.getOnlyElement(changeMessages.get(ps1));
+    assertEquals("Testing trailing double newline\n" + "\n", cm1.getMessage());
+    assertEquals(changeOwner.getAccount().getId(), cm1.getAuthor());
+
   }
 
   @Test
@@ -736,6 +763,7 @@ public class ChangeNotesTest {
         + "\n"
         + "Testing paragraph 3");
     update.commit();
+    PatchSet.Id ps1 = c.currentPatchSetId();
 
     RevWalk walk = new RevWalk(repo);
     try {
@@ -756,15 +784,54 @@ public class ChangeNotesTest {
     }
 
     ChangeNotes notes = newNotes(c);
-    List<String> changeMessages = notes.getChangeMessages();
-    assertEquals(1, changeMessages.size());
+    ListMultimap<PatchSet.Id, ChangeMessage> changeMessages =
+        notes.getChangeMessages();
+    assertEquals(1, changeMessages.keySet().size());
+
+    ChangeMessage cm1 = Iterables.getOnlyElement(changeMessages.get(ps1));
     assertEquals("Testing paragraph 1\n"
         + "\n"
         + "Testing paragraph 2\n"
         + "\n"
-        + "Testing paragraph 3", changeMessages.get(0));
+        + "Testing paragraph 3", cm1.getMessage());
+    assertEquals(changeOwner.getAccount().getId(), cm1.getAuthor());
   }
 
+  @Test
+  public void changeMessageMultipleInOnePatchSet() throws Exception {
+    Change c = newChange();
+    ChangeUpdate update = newUpdate(c, changeOwner);
+    update.putReviewer(changeOwner.getAccount().getId(), REVIEWER);
+    update.setChangeMessage("First change message.\n");
+    update.commit();
+
+    PatchSet.Id ps1 = c.currentPatchSetId();
+
+    update = newUpdate(c, changeOwner);
+    update.putReviewer(changeOwner.getAccount().getId(), REVIEWER);
+    update.setChangeMessage("Second change message.\n");
+    update.commit();
+
+    ChangeNotes notes = newNotes(c);
+    ListMultimap<PatchSet.Id, ChangeMessage> changeMessages =
+        notes.getChangeMessages();
+    assertEquals(1, changeMessages.keySet().size());
+
+    List<ChangeMessage> cm = changeMessages.get(ps1);
+    assertEquals(2, cm.size());
+    assertEquals("Second change message.\n",
+        cm.get(0).getMessage());
+    assertEquals(changeOwner.getAccount().getId(),
+        cm.get(0).getAuthor());
+    assertEquals(ps1, cm.get(0).getPatchSetId());
+    assertEquals("First change message.\n",
+        cm.get(1).getMessage());
+    assertEquals(changeOwner.getAccount().getId(),
+        cm.get(0).getAuthor());
+    assertEquals(ps1, cm.get(0).getPatchSetId());
+  }
+
+
   private Change newChange() {
     Change.Id changeId = new Change.Id(1);
     Change c = new Change(