Merge branch 'card-list': the thread pane as a list of cards

Replaces the five-column grid with a single column of three-line cards. Item 53
recorded that the columns, not the cues drawn inside them, were what made the
list read as a table of records; item 20 had already shipped finished, tested
and green and been rejected on sight for exactly that reason.

A card is sender and date, subject with the flag, attachment and reply-count
marks, and tags, at one uniform height. Replies indent under a continuous spine
and show only the tags their thread does not carry. The account colour runs down
the card's left edge, replacing the chip that used to eat a third of every
subject line, with matching swatches in the account dropdown. Sorting newest or
oldest first is new and remembered.

Closes items 20, 51, 53 and 60.

The four defects that mattered were all found by rendering cards to an image and
looking at them, with the suite green through every one: a date clipped on unread
cards because bold is wider than the font the layout measured, an accent bar
painted in a colour identical to the background, an expander pill in a palette
role a theme had made equal to Base, and three separate faults from trusting
notmuch's reply depth to mean structure when it only means how notmuch happened
to thread the mail.

1 files changed, 21 insertions, 18 deletions

diff --git a/src/threadlistview.h b/src/threadlistview.h
index 0b4eafc..3215153 100644
--- a/src/threadlistview.h
+++ b/src/threadlistview.h
@@ -18,30 +18,33 @@
 
 #pragma once
 
-#include <QTableView>
+#include <QTreeView>
 
-/// The thread list, with a row-wide strip of tag chips under each row's cells.
+/// The thread list.
 ///
-/// The strip is painted by the VIEW rather than by a delegate, and that is the
-/// whole reason this class exists. A delegate is handed one cell's rectangle
-/// and cannot paint outside its column, so pills drawn from the subject
-/// column's delegate stop at that column's edge, losing the last tags of a
-/// well-tagged thread, and start at that column's left edge, which puts them
-/// under the subject instead of under the row. Painting after the cells lets
-/// the strip run the full width, which is what the layout asks for:
+/// It exists for ONE reason now: the expander is drawn by CardDelegate, and a
+/// delegate gets no click of its own without an editor, so the view has to own
+/// the hit-test. Everything else it used to do is gone.
 ///
-///     [ date ][ from ][ subject ...................... ]
-///       [ pill ][ pill ][ pill ]
-///
-/// The cells confine themselves to the upper band so the lower one is free;
-/// SubjectDelegate::kRowPadding and rowHeightFor() are the shared measurements
-/// that keep the two halves agreeing.
-class ThreadListView : public QTableView
+/// Until item 53 this class also painted a row-wide strip of tag chips after
+/// the cells, because a delegate cannot paint outside its column and the strip
+/// spanned all five. With one column and one delegate painting the whole card,
+/// that reason is gone and so is the paintEvent, along with the two faults it
+/// kept producing: a deleted row cut in half, and every other row showing a
+/// bare stripe, both from the view having to re-honour alternating colours,
+/// the selection and BackgroundRole across cells it did not own.
+class ThreadListView : public QTreeView
 {
     Q_OBJECT
 public:
-    using QTableView::QTableView;
+    using QTreeView::QTreeView;
 
 protected:
-    void paintEvent(QPaintEvent *event) override;
+    /// Toggles a thread when its reply count is clicked.
+    ///
+    /// Being VISIBLE and being CLICKABLE are separate properties:
+    /// setRootIsDecorated(false), needed to stop the style drawing its own
+    /// indicator underneath, also removed the style's hit area, so an expander
+    /// once painted correctly and did nothing at all.
+    void mousePressEvent(QMouseEvent *event) override;
 };