From d8c493109a810bba2d8d4c5d048087a4671f875b Mon Sep 17 00:00:00 2001
From: Wyatt Allen <wyatta@google.com>
Date: Tue, 3 Oct 2017 10:08:15 +0100
Subject: [PATCH] Add Gerrit-Comment-In-Reply-To footer

Change-Id: I7860838077cb303331a50ac2855441534bb26d10
---
 Documentation/user-notify.txt                 | 11 +++++++
 .../server/mail/send/CommentSender.java       | 33 +++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/Documentation/user-notify.txt b/Documentation/user-notify.txt
index 4b928f3509..3c922ed716 100644
--- a/Documentation/user-notify.txt
+++ b/Documentation/user-notify.txt
@@ -244,6 +244,17 @@ In comment emails, the has-labels footer states whether label votes had
 been posted in that notification using "Yes" or "No", for
 example `Gerrit-HasLabels: No`.
 
+[[Gerrit-Comment-In-Reply-To]]Gerrit-Comment-In-Reply-To::
+
+In comment emails, a comment-in-reply-to footer is present for each
+account who has a comment that is replied-to in that set of comments.
+For example, to apply a filter to Gerrit messages in which your own diff
+comments are responded to, you might search for the following:
+
+----
+  Gerrit-Comment-In-Reply-To: User Name <user@example.com>
+----
+
 GERRIT
 ------
 Part of link:index.html[Gerrit Code Review]
diff --git a/java/com/google/gerrit/server/mail/send/CommentSender.java b/java/com/google/gerrit/server/mail/send/CommentSender.java
index 805527300f..fae42746f0 100644
--- a/java/com/google/gerrit/server/mail/send/CommentSender.java
+++ b/java/com/google/gerrit/server/mail/send/CommentSender.java
@@ -22,6 +22,7 @@ import com.google.gerrit.common.data.FilenameComparator;
 import com.google.gerrit.common.errors.EmailException;
 import com.google.gerrit.common.errors.NoSuchEntityException;
 import com.google.gerrit.extensions.api.changes.NotifyHandling;
+import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gerrit.reviewdb.client.Comment;
 import com.google.gerrit.reviewdb.client.Patch;
@@ -243,6 +244,34 @@ public class CommentSender extends ReplyToChangeSender {
     return groups;
   }
 
+  /** Get the set of accounts whose comments have been replied to in this email. */
+  private HashSet<Account.Id> getReplyAccounts() {
+    HashSet<Account.Id> replyAccounts = new HashSet<>();
+
+    // Track visited parent UUIDs to avoid cycles.
+    HashSet<String> visitedUuids = new HashSet<>();
+
+    for (Comment comment : inlineComments) {
+      visitedUuids.add(comment.key.uuid);
+
+      // Traverse the parent relation to the top of the comment thread.
+      Comment current = comment;
+      while (current.parentUuid != null && !visitedUuids.contains(current.parentUuid)) {
+        Optional<Comment> optParent = getParent(current);
+        if (!optParent.isPresent()) {
+          // There is a parent UUID, but it cannot be loaded, break from the comment thread.
+          break;
+        }
+
+        Comment parent = optParent.get();
+        replyAccounts.add(parent.author.getId());
+        visitedUuids.add(current.parentUuid);
+        current = parent;
+      }
+    }
+    return replyAccounts;
+  }
+
   private String getCommentLinePrefix(Comment comment) {
     int lineNbr = comment.range == null ? comment.lineNbr : comment.range.startLine;
     StringBuilder sb = new StringBuilder();
@@ -497,6 +526,10 @@ public class CommentSender extends ReplyToChangeSender {
     footers.add("Gerrit-Comment-Date: " + getCommentTimestamp());
     footers.add("Gerrit-HasComments: " + (hasComments ? "Yes" : "No"));
     footers.add("Gerrit-HasLabels: " + (labels.isEmpty() ? "No" : "Yes"));
+
+    for (Account.Id account : getReplyAccounts()) {
+      footers.add("Gerrit-Comment-In-Reply-To: " + getNameEmailFor(account));
+    }
   }
 
   private String getLine(PatchFile fileInfo, short side, int lineNbr) {