cmd/gerritbot: greet with the GitHub username for the PR rule findings comment

Use the GitHub username (e.g., "thepudds") to greet the
CL author when we report possible problems, rather
than using their email.

Updates golang/go#61573

Change-Id: I3699dc4e72c6244cd5d13493e5e4bd7cb098430a
Reviewed-on: https://go-review.googlesource.com/c/build/+/520116
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
Run-TryBot: t hepudds <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: thepudds

cmd/gerritbot/gerritbot.go

@@ -789,6 +789,10 @@ Please visit Gerrit at %s.
 		problems := rules.Check(change)
 		if len(problems) > 0 {
 			summary := rules.FormatResults(problems)
+			user := author
+			if pr.User != nil && pr.User.Login != nil {
+				user = *pr.User.Login
+			}
 			// If needed, summary contains advice for how to edit the commit message.
 			msg := fmt.Sprintf("Hello %v, I've spotted some possible problems.\n\n"+
 				"These findings are based on simple heuristics. If a finding appears wrong, briefly reply here saying so. "+
@@ -798,7 +802,7 @@ Please visit Gerrit at %s.
 				"(In general for Gerrit code reviews, the CL author is expected to close out each piece of feedback by "+
 				"marking it as 'Done' if implemented as suggested or otherwise reply to each review comment. "+
 				"See the [Review](https://go.dev/doc/contribute#review) section of the Contributing Guide for details.)",
-				author, summary)
+				user, summary)
 
 			gcl, err := b.gerritChangeForPR(pr)
 			if err != nil {