Merge branch 'zy/send-email-error-handling'

Auth-related (and unrelated) error handling in send-email has been
made more robust.

* zy/send-email-error-handling:
  send-email: finer-grained SMTP error handling
  send-email: capture errors in an eval {} block

Author: gitster

git-send-email.perl

@@ -1419,7 +1419,7 @@ sub smtp_auth_maybe {
 		die "invalid smtp auth: '${smtp_auth}'";
 	}
 
-	# TODO: Authentication may fail not because credentials were
+	# Authentication may fail not because credentials were
 	# invalid but due to other reasons, in which we should not
 	# reject credentials.
 	$auth = Git::credential({
@@ -1431,24 +1431,61 @@ sub smtp_auth_maybe {
 		'password' => $smtp_authpass
 	}, sub {
 		my $cred = shift;
+		my $result;
+		my $error;
+
+		# catch all SMTP auth error in a unified eval block
+		eval {
+			if ($smtp_auth) {
+				my $sasl = Authen::SASL->new(
+					mechanism => $smtp_auth,
+					callback => {
+						user     => $cred->{'username'},
+						pass     => $cred->{'password'},
+						authname => $cred->{'username'},
+					}
+				);
+				$result = $smtp->auth($sasl);
+			} else {
+				$result = $smtp->auth($cred->{'username'}, $cred->{'password'});
+			}
+			1; # ensure true value is returned if no exception is thrown
+		} or do {
+			$error = $@ || 'Unknown error';
+		};
+
+		return ($error
+			? handle_smtp_error($error)
+			: ($result ? 1 : 0));
+	});
 
-		if ($smtp_auth) {
-			my $sasl = Authen::SASL->new(
-				mechanism => $smtp_auth,
-				callback => {
-					user => $cred->{'username'},
-					pass => $cred->{'password'},
-					authname => $cred->{'username'},
-				}
-			);
+	return $auth;
+}
 
-			return !!$smtp->auth($sasl);
+sub handle_smtp_error {
+	my ($error) = @_;
+
+	# Parse SMTP status code from error message in:
+	# https://www.rfc-editor.org/rfc/rfc5321.html
+	if ($error =~ /\b(\d{3})\b/) {
+		my $status_code = $1;
+		if ($status_code =~ /^4/) {
+			# 4yz: Transient Negative Completion reply
+			warn "SMTP transient error (status code $status_code): $error";
+			return 1;
+		} elsif ($status_code =~ /^5/) {
+			# 5yz: Permanent Negative Completion reply
+			warn "SMTP permanent error (status code $status_code): $error";
+			return 0;
 		}
+		# If no recognized status code is found, treat as transient error
+		warn "SMTP unknown error: $error. Treating as transient failure.";
+		return 1;
+	}
 
-		return !!$smtp->auth($cred->{'username'}, $cred->{'password'});
-	});
-
-	return $auth;
+	# If no status code is found, treat as transient error
+	warn "SMTP generic error: $error";
+	return 1;
 }
 
 sub ssl_verify_params {