feat(placeholder): count sent mail and drafts on the blank pane

Item 67. The pane counted unread, flagged and inbox from three fixed
tag: queries. Sent and drafts cannot join that list as tags: tag:draft
counts 0 against a real database and no draft-ish tag exists in it at
all, so a tag-based line would be a permanent zero that reads as working
code. Both are composed from each account's folder keys instead, the
same way the Sent view already composes its query.

The drafts key was parsed and documented as unused in v1. Composing
drafts is still v2; counting them is not, so Account::draftsQuery() and
Config::allDraftsQuery() now mirror the sent pair. The shared body moved
into folderQuery() and joinAccountQueries(), so the load-bearing quoting
(a provider nests both folders under a bracketed parent, and [ and ] are
Xapian syntax) and the bare-"or" guard exist once rather than once per
folder type.

The fixed array is gone rather than extended. It held queries and labels
in two lists indexed in parallel, which is a hazard that grows with the
list: an entry inserted in one and not the other prints a real number
against the wrong name and looks entirely plausible. placeholderLines()
carries each query beside the callable that labels it, so the two cannot
drift, and the count reply stays paired by position as the worker
requires.

A line is omitted when no account configures that folder rather than
shown as 0, following item 63: a missing folder is a real configuration,
and "0 sent" claims the user has sent nothing.

Measured against the real config: 4 sent terms over 601 threads, 5
drafts terms over 3, the extra drafts term coming from the one account
that configures drafts and no sent, which is what proves the two are
collected independently.

Four tests here and four in test_config, mutation-checked at three
points: dropping the drafts line, an off-by-one in the label pairing,
and removing the -1 guard for an uncountable query. Each mutation fails
a test.

1 files changed, 56 insertions, 27 deletions

diff --git a/src/mainwindow.cpp b/src/mainwindow.cpp
index be6cfdb..824bdca 100644
--- a/src/mainwindow.cpp
+++ b/src/mainwindow.cpp
@@ -1385,40 +1385,73 @@ void MainWindow::onAllTagsReady(const QStringList &tags)
     m_queryCompleter->setTags(tags);
 }
 
-namespace {
+QList<MainWindow::PlaceholderLine> MainWindow::placeholderLines() const
+{
+    // One list of (query, label-maker) pairs rather than two arrays indexed in
+    // parallel. The parallel version is what the fixed array was, and its
+    // hazard is that inserting an entry in one and not the other prints a real
+    // number against the wrong name, which reads as a plausible pane.
+    //
+    // The queries are wire format and deliberately untranslated: `tag:` is
+    // notmuch syntax, not user-facing prose. Only the labels are translated.
+    QList<PlaceholderLine> lines = {
+        { QStringLiteral("tag:unread"),
+          [this](int n) { return tr("%n unread", "", n); } },
+        { QStringLiteral("tag:flagged"),
+          [this](int n) { return tr("%n flagged", "", n); } },
+        { QStringLiteral("tag:inbox"),
+          [this](int n) { return tr("%n in inbox", "", n); } },
+    };
 
-/// The queries behind the placeholder's helper lines, in render order.
-///
-/// Wire format, deliberately untranslated: `tag:` is notmuch syntax, not user
-/// -facing prose. Only the labels beside them are translated.
-const std::array<const char *, 3> kPlaceholderQueries = {
-    "tag:unread",
-    "tag:flagged",
-    "tag:inbox",
-};
+    // Sent and drafts are composed from the account folders, not from a tag.
+    // `tag:draft` counts 0 against a real database and no draft-ish tag exists
+    // in it, so a tag-based line would be a permanent zero.
+    //
+    // Omitted entirely when no account configures the folder, rather than
+    // shown as 0: item 63 established that a missing sent folder is a real
+    // configuration, and "0 sent" claims the user has sent nothing.
+    const QString sent = m_config.allSentQuery();
+    if (!sent.isEmpty()) {
+        lines.append({ sent, [this](int n) { return tr("%n sent", "", n); } });
+    }
 
-} // namespace
+    const QString drafts = m_config.allDraftsQuery();
+    if (!drafts.isEmpty()) {
+        lines.append({ drafts,
+                       [this](int n) { return tr("%n draft(s)", "", n); } });
+    }
+
+    return lines;
+}
+
+QStringList MainWindow::placeholderQueries() const
+{
+    QStringList queries;
+    for (const PlaceholderLine &line : placeholderLines())
+        queries.append(line.query);
+    return queries;
+}
 
 QList<HtmlBuilder::PlaceholderHelper> MainWindow::placeholderHelpers() const
 {
     QList<HtmlBuilder::PlaceholderHelper> helpers;
 
-    // Empty until the first reply lands. Rendering three zeroes meanwhile
-    // would be worse than rendering nothing: a zero is a claim.
-    if (m_placeholderCounts.size() == int(kPlaceholderQueries.size())) {
-        const QStringList labels = {
-            tr("%n unread", "", m_placeholderCounts.at(0)),
-            tr("%n flagged", "", m_placeholderCounts.at(1)),
-            tr("%n in inbox", "", m_placeholderCounts.at(2)),
-        };
+    const QList<PlaceholderLine> lines = placeholderLines();
 
-        for (int i = 0; i < labels.size(); ++i) {
+    // Empty until the first reply lands. Rendering zeroes meanwhile would be
+    // worse than rendering nothing: a zero is a claim.
+    //
+    // The size check is also what keeps the pairing honest across a config
+    // that changed shape between the request and the reply: counts that do not
+    // match the current line list are not this list's answers.
+    if (m_placeholderCounts.size() == lines.size()) {
+        for (int i = 0; i < lines.size(); ++i) {
             // A query notmuch could not count yields -1; skip that line rather
             // than print a negative number at the user.
             if (m_placeholderCounts.at(i) < 0)
                 continue;
-            helpers.append({ labels.at(i),
-                             QString::fromLatin1(kPlaceholderQueries[i]) });
+            helpers.append({ lines.at(i).label(m_placeholderCounts.at(i)),
+                             lines.at(i).query });
         }
     }
 
@@ -1438,12 +1471,8 @@ void MainWindow::showPlaceholderPane()
 {
     m_messageView->showPlaceholder(placeholderHelpers());
 
-    QStringList queries;
-    for (const char *query : kPlaceholderQueries)
-        queries.append(QString::fromLatin1(query));
-
     QMetaObject::invokeMethod(m_worker, "requestCounts", Qt::QueuedConnection,
-                              Q_ARG(QStringList, queries),
+                              Q_ARG(QStringList, placeholderQueries()),
                               Q_ARG(quint64, ++m_countsGeneration));
 }