feat: let a row say whether it is a conversation

One predicate for the question every scope, label and membership decision
in item 177 keys on. It repeats hasChildren()'s rule deliberately: an
expander and a conversation are the same fact, including that a loaded
thread trusts its children over a count that included duplicates.

3 files changed, 110 insertions, 0 deletions

diff --git a/src/threadlistmodel.cpp b/src/threadlistmodel.cpp
index f085b79..1bda728 100644
--- a/src/threadlistmodel.cpp
+++ b/src/threadlistmodel.cpp
@@ -1014,6 +1014,29 @@ bool ThreadListModel::isMessageRow(const QModelIndex &index) const
     return index.isValid() && index.parent().isValid();
 }
 
+bool ThreadListModel::isConversationRow(const QModelIndex &index) const
+{
+    if (!index.isValid() || isMessageRow(index))
+        return false;
+    if (index.row() < 0 || index.row() >= m_threads.size())
+        return false;
+
+    // A flat view has no conversations by construction: every row is one
+    // message and there is nothing to expand.
+    if (m_flatMode)
+        return false;
+
+    const ThreadNode &node = m_threads.at(index.row());
+
+    // Identical to hasChildren()'s rule, and deliberately so: an expander and a
+    // conversation are the same fact. Once loaded the children are the truth,
+    // which is how a thread whose totalCount counted DUPLICATES stops claiming
+    // to be a conversation it cannot open.
+    if (node.loaded)
+        return !node.children.isEmpty();
+    return node.summary.totalCount > 1;
+}
+
 MessageNode ThreadListModel::messageAt(const QModelIndex &index) const
 {
     if (!isMessageRow(index))
diff --git a/src/threadlistmodel.h b/src/threadlistmodel.h
index 4af09d8..d1baae1 100644
--- a/src/threadlistmodel.h
+++ b/src/threadlistmodel.h
@@ -324,6 +324,14 @@ public:
     /// True when the index is a message row rather than a thread root.
     bool isMessageRow(const QModelIndex &index) const;
 
+    /// Whether this row stands for a CONVERSATION rather than for one message.
+    ///
+    /// The single question every scope, label and membership decision keys on
+    /// (item 177). A row with replies is the conversation; a row without them
+    /// is its message and behaves as it always has. A message row is never
+    /// either, so the answer is false there rather than undefined.
+    bool isConversationRow(const QModelIndex &index) const;
+
     /// The message row's node, or a default-constructed one for any index that
     /// is not a message row.
     MessageNode messageAt(const QModelIndex &index) const;
diff --git a/tests/test_threadlistmodel.cpp b/tests/test_threadlistmodel.cpp
index 9ca35e3..df579e6 100644
--- a/tests/test_threadlistmodel.cpp
+++ b/tests/test_threadlistmodel.cpp
@@ -105,6 +105,10 @@ private slots:
     void aRowCarriesItsSenderAndAccountAddress();
     void aMessageRowCarriesItsOwnSenderAndAddress();
     void aFlatViewsAvatarFollowsTheRecipient();
+    void aSummaryWithOneMessageIsAMessageRow();
+    void aSummaryWithRepliesIsAConversationRow();
+    void aLoadedThreadTrustsItsChildrenOverItsCount();
+    void aMessageRowIsNeverAConversationRow();
 };
 
 static ThreadSummary makeThread(const QString &id, const QString &subject)
@@ -2343,5 +2347,80 @@ void TestThreadListModel::theTrashViewDrawsNoDoomedFill()
     QVERIFY(first.data(Qt::BackgroundRole).isValid());
 }
 
+void TestThreadListModel::aSummaryWithOneMessageIsAMessageRow()
+{
+    ThreadListModel model;
+    ThreadSummary one = makeThread(QStringLiteral("t1"), QStringLiteral("Alone"));
+    one.totalCount = 1;
+    one.firstMessageId = QStringLiteral("m1");
+    model.appendBatch({ one });
+
+    const QModelIndex row = model.index(0, 0, QModelIndex());
+    QVERIFY2(!model.isConversationRow(row),
+             "a thread of one message is not a conversation: it has no replies "
+             "to stand for, and must open its message on one click");
+}
+
+void TestThreadListModel::aSummaryWithRepliesIsAConversationRow()
+{
+    ThreadListModel model;
+    ThreadSummary many = makeThread(QStringLiteral("t1"), QStringLiteral("Talk"));
+    many.totalCount = 4;
+    many.firstMessageId = QStringLiteral("m1");
+    model.appendBatch({ many });
+
+    const QModelIndex row = model.index(0, 0, QModelIndex());
+    QVERIFY(model.isConversationRow(row));
+}
+
+void TestThreadListModel::aLoadedThreadTrustsItsChildrenOverItsCount()
+{
+    // notmuch's totalCount counts duplicates, so a "thread of 2" can load with
+    // no replies at all. Once loaded the children are the truth, exactly as
+    // hasChildren() already decides.
+    ThreadListModel model;
+    ThreadSummary many = makeThread(QStringLiteral("t1"), QStringLiteral("Dupe"));
+    many.totalCount = 2;
+    many.firstMessageId = QStringLiteral("m1");
+    model.appendBatch({ many });
+
+    MessageNode root;
+    root.messageId = QStringLiteral("m1");
+    root.threadId = QStringLiteral("t1");
+    root.depth = 0;
+    model.setThreadMessages(QStringLiteral("t1"), { root });
+
+    const QModelIndex row = model.index(0, 0, QModelIndex());
+    QVERIFY2(!model.isConversationRow(row),
+             "a thread whose count came from duplicates still claims to be a "
+             "conversation after loading no replies at all");
+}
+
+void TestThreadListModel::aMessageRowIsNeverAConversationRow()
+{
+    ThreadListModel model;
+    ThreadSummary many = makeThread(QStringLiteral("t1"), QStringLiteral("Talk"));
+    many.totalCount = 2;
+    many.firstMessageId = QStringLiteral("m1");
+    model.appendBatch({ many });
+
+    MessageNode root;
+    root.messageId = QStringLiteral("m1");
+    root.threadId = QStringLiteral("t1");
+    root.depth = 0;
+    MessageNode reply;
+    reply.messageId = QStringLiteral("m2");
+    reply.threadId = QStringLiteral("t1");
+    reply.depth = 1;
+    model.setThreadMessages(QStringLiteral("t1"), { root, reply });
+
+    const QModelIndex thread = model.index(0, 0, QModelIndex());
+    const QModelIndex replyRow = model.index(0, 0, thread);
+    QVERIFY(model.isMessageRow(replyRow));
+    QVERIFY2(!model.isConversationRow(replyRow),
+             "a reply row answered yes, so an action on it would scope to the "
+             "whole conversation");
+}
+
 QTEST_MAIN(TestThreadListModel)
 #include "test_threadlistmodel.moc"