Restore Plugin HTML After a WebKit Reload

Plugin dialog content is injected with SetPage, so on the WebKit backends a
reload (context menu, keyboard shortcut or location.reload()) re-fetches the
SetPage base URL instead of the injected document, and the plugin UI is gone
for good: load_plugin_content() returned early once m_content_loaded was set.

Re-inject the plugin HTML when a main-frame load after the initial swap is
neither that swap nor a page the plugin linked to. m_own_page_load marks the
load our own SetPage caused, and the URL test recognises the reload: the
injected document and the directory a reload re-fetches both report the base
URL, so a load of any other URL is left alone. The test ignores a fragment the
page navigated to, and undoes the escaping the web view applies to what the
resources path holds. A load error after the swap is left alone.

No separate MSW path is needed: wxWebViewEdge ignores the SetPage base URL, so
its documents report about:blank and the test never matches there, and WebView2
reloads NavigateToString content from its own history entry anyway.

src/slic3r/GUI/PluginWebDialog.cpp

@@ -8,6 +8,7 @@
 #include <boost/filesystem.hpp>
 
 #include <wx/event.h>
+#include <wx/uri.h>
 
 #include <utility>
 
@@ -55,6 +56,14 @@ wxString web_base_url()
     return wxString("file://") + from_u8(dir) + "/";
 }
 
+// Whether a loaded document is the plugin HTML's own base URL. The web view reports the URL it
+// parsed, so any fragment the page navigated to is ignored and the escaping it applies to what the
+// resources path holds (a space, a non-ASCII character) is undone first.
+bool is_content_url(const wxString& url)
+{
+    return wxURI::Unescape(url.BeforeFirst('#')) == web_base_url();
+}
+
 } // namespace
 
 PluginWebDialog::PluginWebDialog(wxWindow*          parent,
@@ -139,19 +148,31 @@ void PluginWebDialog::destroy_for_plugin(PluginWebDialog* dialog)
 
 void PluginWebDialog::on_bootstrap_event(wxWebViewEvent& event)
 {
-    // The first bootstrap load (or its error) triggers the swap to plugin HTML;
-    // the resulting plugin-page load is ignored (guarded by m_content_loaded).
-    load_plugin_content();
+    // The first bootstrap load (or its error) triggers the swap to plugin HTML.
+    if (!m_content_loaded)
+        load_plugin_content();
+    // WebKit reloads the SetPage base URL rather than the injected page, and the injected document
+    // reports that same URL, so a load of it that is not the swap we started is a browser reload
+    // and the plugin HTML has to be put back. A page the plugin linked to arrives under its own
+    // URL and is left alone; a post-load error only ever means a failed subresource. The Edge
+    // backend ignores the base URL, so the comparison never matches there, and WebView2 reloads
+    // SetPage content from its own history entry anyway.
+    else if (event.GetEventType() == wxEVT_WEBVIEW_LOADED) {
+        if (m_own_page_load)
+            m_own_page_load = false;
+        else if (is_content_url(event.GetURL()))
+            load_plugin_content();
+    }
     event.Skip();
 }
 
 void PluginWebDialog::load_plugin_content()
 {
-    if (m_content_loaded)
-        return;
     m_content_loaded = true;
-    if (wxWebView* wv = browser())
+    if (wxWebView* wv = browser()) {
+        m_own_page_load = true;
         wv->SetPage(wxString::FromUTF8(m_html), web_base_url());
+    }
 }
 
 void PluginWebDialog::on_script_message(const nlohmann::json& payload)

src/slic3r/GUI/PluginWebDialog.hpp

@@ -72,6 +72,7 @@ private:
 
     std::string                   m_html;
     bool                          m_content_loaded{false};
+    bool                          m_own_page_load{false}; // a SetPage of the plugin HTML is in flight
     bool                          m_open{true};
     bool                          m_close_fired{false};
     std::optional<nlohmann::json> m_result;

src/slic3r/GUI/UnsavedChangesDialog.cpp

@@ -891,7 +891,7 @@ void UnsavedChangesDialog::build(Preset::Type type, PresetCollection *dependent_
     top_title_temp_v->Add(top_title_temp_h, 1, wxALIGN_CENTER, 0);
     m_panel_temp->SetSizer(top_title_temp_v);
     m_panel_temp->Layout();
-    m_sizer_top->Add(m_panel_temp, 0, wxALIGN_CENTER, 0);
+    m_sizer_top->Add(m_panel_temp, 1, wxALIGN_CENTER, 0);
 
     title_block_middle = new wxPanel(m_table_top, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxTAB_TRAVERSAL);
     title_block_middle->SetBackgroundColour(wxColour(172, 172, 172));
@@ -935,12 +935,11 @@ void UnsavedChangesDialog::build(Preset::Type type, PresetCollection *dependent_
     m_panel_newv->Layout();
     m_sizer_top->Add(m_panel_newv, 0, wxALIGN_CENTER, 0);
     //m_sizer_top->Add(top_title_newv, 1, wxALIGN_CENTER, 0);
-    m_sizer_top->AddStretchSpacer();
 
     m_table_top->SetSizer(m_sizer_top);
     m_table_top->Layout();
     m_sizer_top->Fit(m_table_top);
-    m_sizer_tab->Add(m_table_top, 0, wxEXPAND, 0);
+    m_sizer_tab->Add(m_table_top, 1, 0, 0);
 
     m_scrolledWindow = new wxScrolledWindow(m_panel_tab, wxID_ANY, wxDefaultPosition, UNSAVE_CHANGE_DIALOG_SCROLL_WINDOW_SIZE,  wxNO_BORDER|wxVSCROLL);
     m_scrolledWindow->SetScrollRate(0, 5);