add diff action extension mechanism for external plugins

Expose Q_PROPERTY lastDiff, signal diffShown(), and Q_INVOKABLE
registerDiffAction() so other KTextEditor plugins (e.g. ollie) can
register actions that appear in the tree view context menu.

When a registered action is picked, computeDiffForFiles() runs
git diff synchronously for the selected files before triggering
the action, ensuring the consumer always gets a fresh diff
regardless of whether the user previously viewed it.

gitplusplus.cpp

@@ -544,6 +544,16 @@ GitPlusPlusView::GitPlusPlusView(GitPlusPlusPlugin *plugin, KTextEditor::MainWin
         auto *diffAction = menu.addAction(QIcon::fromTheme(QStringLiteral("vcs-diff")), diffLabel);
         auto *openAction = menu.addAction(QIcon::fromTheme(QStringLiteral("document-open")), openLabel);
 
+        // Registered diff actions (e.g. "Ollie: Review Diff") — always available
+        QList<QAction *> proxyActions;
+        if (!m_diffActions.isEmpty()) {
+            menu.addSeparator();
+            for (auto *a : m_diffActions) {
+                auto *proxy = menu.addAction(a->icon(), a->text());
+                proxyActions.append(proxy);
+            }
+        }
+
         auto *chosen = menu.exec(m_treeView->viewport()->mapToGlobal(pos));
         if (chosen == diffAction) {
             diffSelected();
@@ -552,6 +562,10 @@ GitPlusPlusView::GitPlusPlusView(GitPlusPlusPlugin *plugin, KTextEditor::MainWin
                 QString absPath = m_gitDir + QLatin1Char('/') + file;
                 m_mainWindow->openUrl(QUrl::fromLocalFile(absPath));
             }
+        } else if (int idx = proxyActions.indexOf(chosen); idx >= 0) {
+            // Compute diff for selected files, then trigger the registered action
+            computeDiffForFiles(files);
+            m_diffActions[idx]->trigger();
         }
     });
 
@@ -694,8 +708,40 @@ void GitPlusPlusView::setMessage(const QString &text, bool isError)
     m_statusLabel->setStyleSheet(isError ? QStringLiteral("color: red;") : QStringLiteral("color: green;"));
 }
 
+void GitPlusPlusView::registerDiffAction(QAction *action)
+{
+    if (action && !m_diffActions.contains(action)) {
+        m_diffActions.append(action);
+        connect(action, &QObject::destroyed, this, [this, action]() {
+            m_diffActions.removeOne(action);
+        });
+    }
+}
+
+void GitPlusPlusView::computeDiffForFiles(const QStringList &files)
+{
+    if (m_gitDir.isEmpty() || files.isEmpty()) return;
+
+    // Compute unstaged diff
+    QStringList args = {QStringLiteral("diff"), QStringLiteral("--")};
+    args.append(files);
+    QByteArray unstaged = GitProcess::run(m_gitDir, args);
+
+    // Compute staged diff
+    QStringList cachedArgs = {QStringLiteral("diff"), QStringLiteral("--cached"), QStringLiteral("--")};
+    cachedArgs.append(files);
+    QByteArray staged = GitProcess::run(m_gitDir, cachedArgs);
+
+    m_lastDiff = staged + unstaged;
+    if (!m_lastDiff.isEmpty())
+        Q_EMIT diffShown(m_lastDiff, QStringLiteral("Review: %1").arg(files.join(QStringLiteral(", "))));
+}
+
 void GitPlusPlusView::showDiffOutput(const QByteArray &diff, const QString &title, const QStringList &gitArgs, int extraFlags)
 {
+    m_lastDiff = diff;
+    Q_EMIT diffShown(diff, title);
+
 #ifdef HAVE_KATE_DIFF
     DiffParams params;
     params.tabTitle = title;

gitplusplus.h

@@ -26,6 +26,7 @@ class QLabel;
 class QComboBox;
 class QCheckBox;
 class QTabWidget;
+class QAction;
 class QSortFilterProxyModel;
 class QStringListModel;
 class QFileSystemWatcher;
@@ -55,11 +56,23 @@ public:
 class GitPlusPlusView : public QObject
 {
     Q_OBJECT
+    Q_PROPERTY(QByteArray lastDiff READ lastDiff NOTIFY diffShown)
 
 public:
     explicit GitPlusPlusView(GitPlusPlusPlugin *plugin, KTextEditor::MainWindow *mainWindow);
     ~GitPlusPlusView() override;
 
+    QByteArray lastDiff() const { return m_lastDiff; }
+
+    /**
+     * Register an external action to appear in the diff context menu.
+     * Ownership stays with the caller.
+     */
+    Q_INVOKABLE void registerDiffAction(QAction *action);
+
+Q_SIGNALS:
+    void diffShown(const QByteArray &diff, const QString &title);
+
 private Q_SLOTS:
     // Status
     void updateStatus();
@@ -128,6 +141,7 @@ private:
     void runSimpleGit(const QStringList &args, const QString &successMsg, const QString &errorMsg);
     void runRemoteGit(const QStringList &args, const QString &opName);
     void setMessage(const QString &text, bool isError = false);
+    void computeDiffForFiles(const QStringList &files);
     void showDiffOutput(const QByteArray &diff, const QString &title, const QStringList &gitArgs = {}, int extraFlags = 0);
     void updateIndicators();
     void setRemoteBusy(bool busy, const QString &opName = {});
@@ -223,6 +237,10 @@ private:
     QString m_workspaceDir;          // this workspace's directory
     QString m_workspaceSourceDir;    // resolved source workspace path
     QStringList m_workspaceRepos;    // repo subdirs in source workspace
+
+    // Diff extension mechanism
+    QByteArray m_lastDiff;
+    QList<QAction *> m_diffActions;
 };
 
 #endif // GITPLUSPLUS_H