mu: remove empty refs + unit-test

Some message can have an _empty_ message-id, e.g. with:
  In-Reply-To: <>
which we weren't filter out.

This would yield and _empty_ Thread-Id, in mu-message.cc

And this would make mu-query believe it had no matches in the first
query, in Query::Private::run_related, and effectively throw away the
results. (Xapian using empty string both for a "not found" result, and
"found an empty string doesn't help either).

So, avoid having an empty reference. Also add a unit-test.

Fixes #2812.

2 files changed, 59 insertions, 3 deletions

diff --git a/lib/message/mu-mime-object.cc b/lib/message/mu-mime-object.cc
index a75da5b..37b9020 100644
--- a/lib/message/mu-mime-object.cc
+++ b/lib/message/mu-mime-object.cc
@@ -1,5 +1,5 @@
 /*
-** Copyright (C) 2022-2023 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+** Copyright (C) 2022-2025 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
 **
 ** This program is free software; you can redistribute it and/or modify it
 ** under the terms of the GNU General Public License as published by the
@@ -426,7 +426,10 @@ MimeMessage::references() const noexcept
 		return seq_some(seq, [&](auto&& str) { return ref == str; });
 	};
 
-	auto is_fake = [](auto&& msgid) {
+	auto on_blacklist = [](auto&& msgid) {
+		// don't include empty message-ids
+		if (!*msgid)
+			return true;
 		// this is bit ugly; protonmail injects fake References which
 		// can otherwise screw up threading.
 		if (g_str_has_suffix(msgid, "protonmail.internalid"))
@@ -447,7 +450,7 @@ MimeMessage::references() const noexcept
 
 		for (auto i = 0; i != g_mime_references_length(mime_refs); ++i) {
 			const auto msgid{g_mime_references_get_message_id(mime_refs, i)};
-			if (msgid && !is_dup(refs, msgid) && !is_fake(msgid))
+			if (msgid && !is_dup(refs, msgid) && !on_blacklist(msgid))
 				refs.emplace_back(msgid);
 		}
 		g_mime_references_free(mime_refs);
diff --git a/lib/tests/test-mu-store-query.cc b/lib/tests/test-mu-store-query.cc
index c79c43f..0baa799 100644
--- a/lib/tests/test-mu-store-query.cc
+++ b/lib/tests/test-mu-store-query.cc
@@ -920,6 +920,57 @@ Boo!
 
 
 static void
+test_related_empty_in_reply_to()
+{
+	g_test_bug("2812");
+	// test message sent to self, and copy of received msg.
+
+	const auto test_msg = R"(From: "Edward Mallory" <ed@leviathan.gb>
+To: "Russ Hildebrandt <russ@example.com>
+Subject: New Prospect
+Date: Wed, 07 Dec 2022 18:38:06 +0200
+Message-ID: <875ysdfentbhg.fsf@djcbsoftware.nl>
+MIME-Version: 1.0
+In-Reply-To: <>
+Content-Type: text/plain
+
+Boo!
+)";
+	const TestMap test_msgs = {
+		{"inbox/cur/msg1", test_msg }};
+
+	TempDir tdir;
+	auto store{make_test_store(tdir.path(), test_msgs, {})};
+
+	g_assert_cmpuint(store.size(), ==, 1);
+
+	// normal query should give 1
+	{
+		auto qr = store.run_query("maildir:/inbox", Field::Id::Date,
+					  QueryFlags::None);
+		assert_valid_result(qr);
+		g_assert_cmpuint(qr->size(), ==, 1);
+	}
+
+	// a related query should also give 1
+	{
+		auto qr = store.run_query("maildir:/inbox", Field::Id::Date,
+					  QueryFlags::IncludeRelated);
+		assert_valid_result(qr);
+		g_assert_cmpuint(qr->size(), ==, 1);
+	}
+
+	// a related/threading query should also give 1
+	{
+		auto qr = store.run_query("maildir:/inbox", Field::Id::Date,
+					  QueryFlags::IncludeRelated | QueryFlags::Threading);
+		assert_valid_result(qr);
+		g_assert_cmpuint(qr->size(), ==, 1);
+	}
+}
+
+
+static void
 test_html()
 {
 	// test message sent to self, and copy of received msg.
@@ -1056,6 +1107,8 @@ main(int argc, char* argv[])
 			test_subject_kata_containers);
 	g_test_add_func("/store/query/related-dup-threaded",
 			test_related_dup_threaded);
+	g_test_add_func("/store/query/related-empty-in-reply-to",
+			test_related_empty_in_reply_to);
 	g_test_add_func("/store/query/html",
 			test_html);
 	g_test_add_func("/store/query/ngrams",