feat: render tags as chips instead of a text column

Spelled out per row, tags ran to 500 pixels of largely repeated text and
took most of the thread list's width. The column is gone; tags render as
coloured chips split by what they actually mean.

An account tag says which mailbox a thread arrived in, and draws as a
chip in front of the subject. A functional tag says what state a thread
is in, and those fill one row under the message pane. One row keeps the
message area from shifting between threads with different tag counts, so
whatever does not fit collapses into a +N chip that names the rest in its
tooltip.

TagColors resolves a colour by exact tag first, then by top-level prefix,
so a single "shopping" entry covers shopping/amazon and shopping/nike
while shopping/amazon can still override its own. That matters at 96
tags. Built-in defaults cover the usual state tags, and anything left
unconfigured falls back to a hash of the name, stable so a chip does not
change colour as the list scrolls.

1 files changed, 126 insertions, 0 deletions

diff --git a/src/tagchip.cpp b/src/tagchip.cpp
new file mode 100644
index 0000000..2e21419
--- /dev/null
+++ b/src/tagchip.cpp
@@ -0,0 +1,126 @@
+/*
+ * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "tagchip.h"
+
+#include <QApplication>
+#include <QFontMetrics>
+#include <QPainter>
+
+#include "tagcolors.h"
+#include "threadlistmodel.h"
+
+namespace TagChip {
+
+QSize sizeFor(const QFontMetrics &metrics, const QString &text)
+{
+    return QSize(metrics.horizontalAdvance(text) + kPaddingX * 2,
+                 metrics.height() + kPaddingY * 2);
+}
+
+void paint(QPainter *painter, const QRect &rect, const QString &text,
+           const QColor &background)
+{
+    painter->save();
+    painter->setRenderHint(QPainter::Antialiasing, true);
+    painter->setPen(Qt::NoPen);
+    painter->setBrush(background);
+    painter->drawRoundedRect(rect, kRadius, kRadius);
+
+    painter->setPen(TagColors::textColourOn(background));
+    painter->drawText(rect, Qt::AlignCenter, text);
+    painter->restore();
+}
+
+}  // namespace TagChip
+
+void SubjectDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option,
+                            const QModelIndex &index) const
+{
+    const QString account =
+        index.data(ThreadListModel::AccountLabelRole).toString();
+    if (account.isEmpty()) {
+        QStyledItemDelegate::paint(painter, option, index);
+        return;
+    }
+
+    // Draw the row's own background and selection first, then the chip and the
+    // subject on top, so a selected or struck-through row still looks right.
+    QStyleOptionViewItem chrome = option;
+    initStyleOption(&chrome, index);
+    chrome.text.clear();
+    const QWidget *widget = option.widget;
+    QStyle *style = widget ? widget->style() : QApplication::style();
+    style->drawControl(QStyle::CE_ItemViewItem, &chrome, painter, widget);
+
+    const QFontMetrics metrics(option.font);
+    const QSize chipSize = TagChip::sizeFor(metrics, account);
+    const QRect chipRect(option.rect.left() + TagChip::kSpacing,
+                         option.rect.top()
+                             + (option.rect.height() - chipSize.height()) / 2,
+                         chipSize.width(), chipSize.height());
+
+    const QColor colour =
+        index.data(ThreadListModel::AccountColourRole).value<QColor>();
+    TagChip::paint(painter, chipRect, account,
+                   colour.isValid() ? colour : QColor(0x55, 0x55, 0x5f));
+
+    // The subject follows the chip, elided so a long one cannot overflow.
+    QRect textRect = option.rect;
+    textRect.setLeft(chipRect.right() + TagChip::kSpacing * 2);
+    if (textRect.width() <= 0)
+        return;
+
+    painter->save();
+    // The model supplies the row's colours; honouring them keeps a deleted
+    // thread white-on-red here as everywhere else.
+    const QVariant foreground = index.data(Qt::ForegroundRole);
+    if (foreground.isValid())
+        painter->setPen(foreground.value<QBrush>().color());
+    else if (option.state & QStyle::State_Selected)
+        painter->setPen(option.palette.highlightedText().color());
+    else
+        painter->setPen(option.palette.text().color());
+
+    // The model's font carries bold for unread and strike-out for deleted.
+    // initStyleOption() already resolved it into chrome.font; using it rather
+    // than option.font is what keeps those cues on a delegate-drawn subject.
+    const QVariant fontData = index.data(Qt::FontRole);
+    const QFont rowFont = fontData.isValid() ? fontData.value<QFont>()
+                                             : chrome.font;
+    painter->setFont(rowFont);
+    const QFontMetrics rowMetrics(rowFont);
+    painter->drawText(textRect, Qt::AlignVCenter | Qt::AlignLeft,
+                      rowMetrics.elidedText(index.data(Qt::DisplayRole).toString(),
+                                            Qt::ElideRight, textRect.width()));
+    painter->restore();
+}
+
+QSize SubjectDelegate::sizeHint(const QStyleOptionViewItem &option,
+                                const QModelIndex &index) const
+{
+    QSize size = QStyledItemDelegate::sizeHint(option, index);
+    const QString account =
+        index.data(ThreadListModel::AccountLabelRole).toString();
+    if (!account.isEmpty()) {
+        const QFontMetrics metrics(option.font);
+        size.setWidth(size.width() + TagChip::sizeFor(metrics, account).width()
+                      + TagChip::kSpacing * 3);
+    }
+    return size;
+}