dashboard/app: extend email reply when bug is not found

We currently reply with a very minimalistic reply that is not too actionable.
Explain what exactly happened and how to fix it.

2 files changed, 53 insertions, 2 deletions

diff --git a/dashboard/app/email_test.go b/dashboard/app/email_test.go
index 3cc0cb5f4..1fd6a81e8 100644
--- a/dashboard/app/email_test.go
+++ b/dashboard/app/email_test.go
@@ -538,3 +538,36 @@ func TestEmailCrossReportingDup(t *testing.T) {
 		}
 	}
 }
+
+func TestEmailErrors(t *testing.T) {
+	c := NewCtx(t)
+	defer c.Close()
+
+	// No reply for email without bug hash and no commands.
+	c.incomingEmail("syzbot@testapp.appspotmail.com", "Investment Proposal")
+	c.expectOK(c.GET("/email_poll"))
+	c.expectEQ(len(c.emailSink), 0)
+
+	// If email contains a command we need to reply.
+	c.incomingEmail("syzbot@testapp.appspotmail.com", "#syz invalid")
+	reply := c.pollEmailBug()
+	c.expectEQ(reply.To, []string{"<default@sender.com>"})
+	c.expectEQ(reply.Body, `> #syz invalid
+
+I see the command but can't find the corresponding bug.
+Please resend the email to syzbot+HASH@testapp.appspotmail.com address
+that is the sender of the bug report (also present in the Reported-by tag).
+
+`)
+
+	c.incomingEmail("syzbot+123@testapp.appspotmail.com", "#syz invalid")
+	reply = c.pollEmailBug()
+	c.expectEQ(reply.Body, `> #syz invalid
+
+I see the command but can't find the corresponding bug.
+The email is sent to  syzbot+HASH@testapp.appspotmail.com address
+but the HASH does not correspond to any known bug.
+Please double check the address.
+
+`)
+}
diff --git a/dashboard/app/reporting_email.go b/dashboard/app/reporting_email.go
index 9707b9e03..2b6ffdc2f 100644
--- a/dashboard/app/reporting_email.go
+++ b/dashboard/app/reporting_email.go
@@ -51,6 +51,14 @@ const (
 	replySubjectPrefix = "Re: "
 	commitHashLen      = 12
 	commitTitleLen     = 47 // so that whole line fits into 78 chars
+
+	replyNoBugID = "I see the command but can't find the corresponding bug.\n" +
+		"Please resend the email to %[1]v address\n" +
+		"that is the sender of the bug report (also present in the Reported-by tag)."
+	replyBadBugID = "I see the command but can't find the corresponding bug.\n" +
+		"The email is sent to  %[1]v address\n" +
+		"but the HASH does not correspond to any known bug.\n" +
+		"Please double check the address."
 )
 
 var mailingLists map[string]bool
@@ -417,7 +425,12 @@ func loadBugInfo(c context.Context, msg *email.Email) (bug *Bug, bugReporting *B
 			log.Infof(c, "no bug ID (%q)", msg.Subject)
 		} else {
 			log.Errorf(c, "no bug ID (%q)", msg.Subject)
-			if err := replyTo(c, msg, "Can't find the corresponding bug.", nil); err != nil {
+			from, err := email.AddAddrContext(ownEmail(c), "HASH")
+			if err != nil {
+				log.Errorf(c, "failed to format sender email address: %v", err)
+				from = "ERROR"
+			}
+			if err := replyTo(c, msg, fmt.Sprintf(replyNoBugID, from), nil); err != nil {
 				log.Errorf(c, "failed to send reply: %v", err)
 			}
 		}
@@ -426,7 +439,12 @@ func loadBugInfo(c context.Context, msg *email.Email) (bug *Bug, bugReporting *B
 	bug, _, err := findBugByReportingID(c, msg.BugID)
 	if err != nil {
 		log.Errorf(c, "can't find bug: %v", err)
-		if err := replyTo(c, msg, "Can't find the corresponding bug.", nil); err != nil {
+		from, err := email.AddAddrContext(ownEmail(c), "HASH")
+		if err != nil {
+			log.Errorf(c, "failed to format sender email address: %v", err)
+			from = "ERROR"
+		}
+		if err := replyTo(c, msg, fmt.Sprintf(replyBadBugID, from), nil); err != nil {
 			log.Errorf(c, "failed to send reply: %v", err)
 		}
 		return nil, nil, nil