Merge: searching from the message pane (item 85)

Five surfaces in the message pane offer a search built from what they show:
the header's subject and date, its sender and recipients on a single-message
thread, a tag chip, a body selection, and every header per message in the
details dialog. Each offers Search for this, which replaces the query, and
Add to search, which narrows it.

The details dialog became labelled rows along the way, which the user wanted
independently of this feature.

Hand tested through every surface, including the case the parenthesising
exists for: adding a sender to 'tag:inbox or tag:flagged' narrows it rather
than widening it.

1 files changed, 87 insertions, 0 deletions

diff --git a/src/messagedetailsdialog.h b/src/messagedetailsdialog.h
new file mode 100644
index 0000000..f865913
--- /dev/null
+++ b/src/messagedetailsdialog.h
@@ -0,0 +1,87 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include <QDialog>
+#include <QList>
+#include <QString>
+
+#include "htmlbuilder.h"
+
+/// One header of one message, as shown and as searched for.
+///
+/// The query is built when the row is, from the parsed value, so nothing has
+/// to parse displayed text back into structure. That is the whole reason this
+/// dialog stopped being a text box.
+struct HeaderRow
+{
+    /// notmuch's field name, or empty for a header with no searchable form.
+    /// Wire format, never translated.
+    QString field;
+
+    /// Translated label shown at the start of the row, e.g. "From:".
+    QString label;
+
+    /// The header's value, verbatim and untrusted.
+    QString value;
+
+    /// The finished query, empty when the header has no searchable form.
+    QString query;
+
+    /// Which message of the thread this row belongs to, zero-based.
+    int messageIndex = 0;
+};
+
+/// The full headers of every message in a thread, read-only.
+///
+/// Rows rather than one text box, so a value can carry its own context menu
+/// without anything parsing rendered text back into structure. The user also
+/// asked not to be shown a text box.
+///
+/// **Every value label is explicitly `Qt::PlainText`.** This replaced a
+/// `QPlainTextEdit` whose plain-textness was a security property rather than a
+/// style: header values come from strangers, and plain text cannot interpret
+/// markup, so there is nothing to escape and nothing that can render. A QLabel
+/// guesses under `Qt::AutoText`, so stating the format is what preserves that.
+class MessageDetailsDialog : public QDialog
+{
+    Q_OBJECT
+public:
+    explicit MessageDetailsDialog(const QList<ThreadRenderItem> &items,
+                                  QWidget *parent = nullptr);
+
+    /// The rows on display, in order. Exposed for testing without rendering.
+    QList<HeaderRow> rows() const { return m_rows; }
+
+    /// Emits searchRequested for `row`, or nothing when the row carries no
+    /// searchable query. The menu entries call this; a test can too, without
+    /// popping a menu.
+    void requestSearch(const HeaderRow &row, bool extend);
+
+signals:
+    /// The user chose a search from a row's menu. `extend` narrows the current
+    /// query rather than replacing it.
+    void searchRequested(const QString &query, bool extend);
+
+private:
+    /// Builds the rows from the thread, one group per message.
+    void buildRows(const QList<ThreadRenderItem> &items);
+
+    QList<HeaderRow> m_rows;
+};