feat(compose): the signature follows the account until it is chosen

A From: change re-seeds the signature from the newly selected account, and
stops doing so the moment the user picks one from the switch. Re-seeding
unconditionally is the one behaviour that can silently discard a deliberate
choice made a moment earlier; this is the shape send_html already uses.

seededSignatureName() reads the combo rather than the context, which
records where the composer opened and does not follow a change to it.

Part of item 152.

2 files changed, 141 insertions, 5 deletions

diff --git a/src/composewindow.cpp b/src/composewindow.cpp
index 8236d79..94a3f46 100644
--- a/src/composewindow.cpp
+++ b/src/composewindow.cpp
@@ -406,8 +406,22 @@ void ComposeWindow::buildUi()
     for (QLineEdit *field : { m_to, m_cc, m_bcc, m_subject })
         connect(field, &QLineEdit::textChanged, this, &ComposeWindow::markDirty);
     connect(m_sendHtml, &QCheckBox::toggled, this, &ComposeWindow::markDirty);
-    connect(m_from, &QComboBox::currentIndexChanged, this,
-            &ComposeWindow::markDirty);
+    connect(m_from, &QComboBox::currentIndexChanged, this, [this]() {
+        markDirty();
+        // The account SEEDS the signature, so a change to it re-seeds. It
+        // stops the moment the user picks one: re-seeding unconditionally is
+        // the one behaviour that can silently discard a deliberate choice
+        // made a moment earlier. Same shape as send_html, which seeds from
+        // context and is then left alone.
+        if (m_signatureChosen)
+            return;
+        const QString seeded = seededSignatureName();
+        if (!Signatures::names(m_signatureDir).contains(seeded)) {
+            applySignature(QString());
+            return;
+        }
+        applySignature(seeded);
+    });
 }
 
 void ComposeWindow::buildFormatToolbar()
@@ -708,9 +722,12 @@ QStringList ComposeWindow::knownSignatures() const
 
 QString ComposeWindow::seededSignatureName() const
 {
-    // The account SEEDS, it does not bind: this is a starting value, and the
-    // switch keeps every signature reachable whichever account is selected.
-    const Account account = m_config.account(m_context.accountKey);
+    // The COMBO, not m_context: the context records where the composer opened
+    // and does not follow a From: change, so reading it would seed the
+    // original account's signature for ever.
+    const QString key = m_from->currentData().toString();
+    const Account account =
+        m_config.account(key.isEmpty() ? m_context.accountKey : key);
     if (!account.signature.isEmpty())
         return account.signature;
     return m_config.compose().signature;
diff --git a/tests/test_composewindow.cpp b/tests/test_composewindow.cpp
index 04d3115..8221ce3 100644
--- a/tests/test_composewindow.cpp
+++ b/tests/test_composewindow.cpp
@@ -17,6 +17,7 @@
  */
 
 #include <QtTest>
+#include <QComboBox>
 #include <QDir>
 #include <QFile>
 #include <QMenu>
@@ -43,6 +44,8 @@ private slots:
     void aResumedDraftSeedsNoSignature();
     void anUnknownSignatureNameSeedsNothing();
     void theSwitchListsEveryFileAndNone();
+    void changingTheAccountFollowsItsSignature();
+    void changingTheAccountStopsFollowingOnceTheSwitchIsUsed();
 
 private:
     /// A config pointing at a signatures directory holding \p files, with one
@@ -216,5 +219,121 @@ void TestComposeWindow::theSwitchListsEveryFileAndNone()
     QCOMPARE(button->menu()->actions().size(), 3);
 }
 
+void TestComposeWindow::changingTheAccountFollowsItsSignature()
+{
+    for (const auto &entry :
+         QList<QPair<QString, QString>>{
+             { QStringLiteral("work.md"), QStringLiteral("Work sig") },
+             { QStringLiteral("home.md"), QStringLiteral("Home sig") } }) {
+        QFile file(m_signatureDir + QStringLiteral("/") + entry.first);
+        QVERIFY(file.open(QIODevice::WriteOnly | QIODevice::Text));
+        file.write(entry.second.toUtf8());
+        file.close();
+    }
+
+    const QString path = m_dir->path() + QStringLiteral("/qtmaildir.conf");
+    {
+        QFile file(path);
+        QVERIFY(file.open(QIODevice::WriteOnly | QIODevice::Text));
+        QTextStream out(&file);
+        out << "[account.work]\n"
+            << "name = Someone\naddress = someone@example.org\n"
+            << "maildir = work\nsend_command = /bin/cat\n"
+            << "signature = work\n"
+            << "\n[account.home]\n"
+            << "name = Someone\naddress = other@example.org\n"
+            << "maildir = home\nsend_command = /bin/cat\n"
+            << "signature = home\n";
+    }
+    Config config;
+    config.load(path);
+
+    ComposeContext context;
+    context.kind = ComposeContext::Kind::New;
+    context.accountKey = QStringLiteral("work");
+
+    ComposeWindow window(context, config, m_dir->path());
+    window.setSignatureDir(m_signatureDir);
+    window.seedSignature();
+
+    auto *body = window.findChild<QPlainTextEdit *>(QStringLiteral("body"));
+    auto *from = window.findChild<QComboBox *>(QStringLiteral("from"));
+    QVERIFY(body);
+    QVERIFY(from);
+    QVERIFY(body->toPlainText().contains(QStringLiteral("Work sig")));
+
+    // Select the other account by its key, never by index: the order of the
+    // combo is the config's and an index assertion would pass on the wrong one.
+    const int home = from->findData(QStringLiteral("home"));
+    QVERIFY(home >= 0);
+    from->setCurrentIndex(home);
+
+    QVERIFY(body->toPlainText().contains(QStringLiteral("Home sig")));
+    QVERIFY(!body->toPlainText().contains(QStringLiteral("Work sig")));
+}
+
+void TestComposeWindow::changingTheAccountStopsFollowingOnceTheSwitchIsUsed()
+{
+    for (const auto &entry :
+         QList<QPair<QString, QString>>{
+             { QStringLiteral("work.md"), QStringLiteral("Work sig") },
+             { QStringLiteral("home.md"), QStringLiteral("Home sig") },
+             { QStringLiteral("chosen.md"), QStringLiteral("Chosen sig") } }) {
+        QFile file(m_signatureDir + QStringLiteral("/") + entry.first);
+        QVERIFY(file.open(QIODevice::WriteOnly | QIODevice::Text));
+        file.write(entry.second.toUtf8());
+        file.close();
+    }
+
+    const QString path = m_dir->path() + QStringLiteral("/qtmaildir.conf");
+    {
+        QFile file(path);
+        QVERIFY(file.open(QIODevice::WriteOnly | QIODevice::Text));
+        QTextStream out(&file);
+        out << "[account.work]\n"
+            << "name = Someone\naddress = someone@example.org\n"
+            << "maildir = work\nsend_command = /bin/cat\n"
+            << "signature = work\n"
+            << "\n[account.home]\n"
+            << "name = Someone\naddress = other@example.org\n"
+            << "maildir = home\nsend_command = /bin/cat\n"
+            << "signature = home\n";
+    }
+    Config config;
+    config.load(path);
+
+    ComposeContext context;
+    context.kind = ComposeContext::Kind::New;
+    context.accountKey = QStringLiteral("work");
+
+    ComposeWindow window(context, config, m_dir->path());
+    window.setSignatureDir(m_signatureDir);
+    window.seedSignature();
+
+    auto *body = window.findChild<QPlainTextEdit *>(QStringLiteral("body"));
+    auto *from = window.findChild<QComboBox *>(QStringLiteral("from"));
+    auto *button =
+        window.findChild<QToolButton *>(QStringLiteral("signatureSwitch"));
+    QVERIFY(body);
+    QVERIFY(from);
+    QVERIFY(button);
+
+    // The user picks one deliberately.
+    for (QAction *action : button->menu()->actions()) {
+        if (action->data().toString() == QStringLiteral("chosen"))
+            action->trigger();
+    }
+    QVERIFY(body->toPlainText().contains(QStringLiteral("Chosen sig")));
+
+    const int home = from->findData(QStringLiteral("home"));
+    QVERIFY(home >= 0);
+    from->setCurrentIndex(home);
+
+    // The deliberate choice survives the account change. Overwriting it is
+    // the one behaviour that can silently discard something the user just did.
+    QVERIFY(body->toPlainText().contains(QStringLiteral("Chosen sig")));
+    QVERIFY(!body->toPlainText().contains(QStringLiteral("Home sig")));
+}
+
 QTEST_MAIN(TestComposeWindow)
 #include "test_composewindow.moc"