Show option to open widget preview in separate browser in the case of embedded error (#8701)

Fixes #8605 by showing an error panel in the case that the embedded browser cannot be found / loaded. To test, make sure the widget preview can open in the normal case, then replace `FlutterUtils.embeddedBrowser(project)` with `null` to test the error case.

I will be making a separate PR to fix another issue where the widget preview panel seems to render multiple times.

CC @bkonyi

Author: helin24

src/io/flutter/view/ViewUtils.java

@@ -64,27 +64,32 @@ public void presentLabels(@NotNull ToolWindow toolWindow, @NotNull List<String>
 
 
   public void presentClickableLabel(ToolWindow toolWindow, List<LabelInput> labels) {
+    JPanel center = createClickableLabelPanel(labels);
+    replacePanelLabel(toolWindow, center);
+  }
+
+  public JPanel createClickableLabelPanel(List<LabelInput> labels) {
     final JPanel panel = new JPanel(new GridLayout(0, 1));
 
     for (LabelInput input : labels) {
       if (input.listener == null) {
         final JLabel descriptionLabel = new JLabel(wrapWithHtml(input.text));
         descriptionLabel.setBorder(JBUI.Borders.empty(5));
         descriptionLabel.setHorizontalAlignment(SwingConstants.CENTER);
-        panel.add(descriptionLabel, BorderLayout.NORTH);
+        panel.add(descriptionLabel);
       }
       else {
         final LinkLabel<String> linkLabel = new LinkLabel<>(wrapWithHtml(input.text), null);
         linkLabel.setBorder(JBUI.Borders.empty(5));
         linkLabel.setListener(input.listener, null);
         linkLabel.setHorizontalAlignment(SwingConstants.CENTER);
-        panel.add(linkLabel, BorderLayout.SOUTH);
+        panel.add(linkLabel);
       }
     }
 
     final JPanel center = new JPanel(new VerticalFlowLayout(VerticalFlowLayout.MIDDLE));
     center.add(panel);
-    replacePanelLabel(toolWindow, center);
+    return center;
   }
 
   public void replacePanelLabel(ToolWindow toolWindow, JComponent label) {

src/io/flutter/widgetpreview/WidgetPreviewPanel.java

@@ -2,6 +2,7 @@
 
 import com.intellij.execution.ExecutionException;
 import com.intellij.execution.process.ProcessHandler;
+import com.intellij.ide.browsers.BrowserLauncher;
 import com.intellij.openapi.Disposable;
 import com.intellij.openapi.application.ApplicationManager;
 import com.intellij.openapi.diagnostic.Logger;
@@ -30,6 +31,7 @@
 import io.flutter.utils.MostlySilentColoredProcessHandler;
 import io.flutter.utils.OpenApiUtils;
 import io.flutter.view.BrowserUrlProvider;
+import io.flutter.view.EmbeddedBrowser;
 import io.flutter.view.EmbeddedTab;
 import io.flutter.view.ViewUtils;
 import io.flutter.view.WidgetPreviewUrlProvider;
@@ -84,6 +86,7 @@ private void startWidgetPreview() {
         }
 
         if (sdk.getVersion().fullVersion().equals(FlutterSdkVersion.UNKNOWN_VERSION)) {
+          LOG.warn("Flutter SDK version is unknown or incomplete.");
           viewUtils.presentLabels(toolWindow, List.of("A Flutter SDK was found at the location",
                                                       "specified in the settings, however the directory",
                                                       "is in an incomplete state. To fix, shut down the IDE,",
@@ -93,6 +96,7 @@ private void startWidgetPreview() {
         }
 
         if (!sdk.getVersion().canUseWidgetPreview()) {
+          LOG.info("Flutter SDK version is too old for widget preview: " + sdk.getVersion().fullVersion());
           showInfoMessage(FlutterBundle.message("widget.preview.sdk.too.old"));
           return;
         }
@@ -103,6 +107,7 @@ private void startWidgetPreview() {
 
         final PubRoot root = PubRoot.forFile(project.getProjectFile());
         if (root == null) {
+          LOG.warn("Pub root not found for project: " + project.getName());
           showInfoMessage("Pub root could not be found to start widget preview.");
           return;
         }
@@ -116,13 +121,15 @@ private void startWidgetPreview() {
         final ProcessHandler handler = new MostlySilentColoredProcessHandler(command.createGeneralCommandLine(project));
         flutterProcessRef.set(handler);
         Consumer<String> onError = (message) -> {
+          LOG.warn("Widget preview process error: " + message);
           showInfoMessage(FlutterBundle.message("widget.preview.error", message != null ? message : ""));
         };
         Consumer<@NotNull String> onSuccess = this::setUrlAndLoad;
         handler.addProcessListener(new WidgetPreviewListener(urlFuture, isVerboseMode, onError, onSuccess));
         handler.startNotify();
       }
       catch (ExecutionException e) {
+        LOG.error("Failed to execute widget preview command", e);
         throw new RuntimeException(e);
       }
     });
@@ -167,23 +174,40 @@ private void startWidgetPreview() {
 
   // This is intended for the first time we load the panel - save the URL and listen for changes.
   private void setUrlAndLoad(@NotNull String url) {
+    LOG.info("Widget preview URL received: " + url);
     this.urlProvider = new WidgetPreviewUrlProvider(url, new DevToolsUtils().getIsBackgroundBright());
     loadUrl(urlProvider);
     listenForReload();
   }
 
   private void loadUrl(@NotNull BrowserUrlProvider urlProvider) {
+    LOG.info("Embedded browser is available: " + (FlutterUtils.embeddedBrowser(project) != null));
     showInfoMessage(FlutterBundle.message("widget.preview.loading", urlProvider.getBrowserUrl()));
 
     OpenApiUtils.safeInvokeLater(() -> {
-      Optional.ofNullable(
-          FlutterUtils.embeddedBrowser(project))
-        .ifPresent(embeddedBrowser ->
-                   {
-                     embeddedBrowser.openPanel(toolWindow, "Widget Preview", FlutterIcons.Flutter, urlProvider,
-                                               System.out::println,
-                                               null);
-                   });
+      final Consumer<EmbeddedBrowser> onBrowserAvailable = embeddedBrowser -> {
+        embeddedBrowser.openPanel(toolWindow, "Widget Preview", FlutterIcons.Flutter, urlProvider,
+            System.out::println,
+            null);
+      };
+
+      final Runnable onBrowserUnavailable = () -> {
+        final List<io.flutter.utils.LabelInput> inputs = List.of(
+            new io.flutter.utils.LabelInput("Embedded browser is not available."),
+            new io.flutter.utils.LabelInput("Open in external browser", (label, data) -> {
+              BrowserLauncher.getInstance().browse(urlProvider.getBrowserUrl(), null);
+            }));
+        final JPanel panel = viewUtils.createClickableLabelPanel(inputs);
+        ApplicationManager.getApplication().invokeLater(() -> {
+          contentPanel.removeAll();
+          contentPanel.add(panel, BorderLayout.CENTER);
+          contentPanel.revalidate();
+          contentPanel.repaint();
+        });
+      };
+
+      Optional.<EmbeddedBrowser>ofNullable(FlutterUtils.embeddedBrowser(project))
+          .ifPresentOrElse(onBrowserAvailable, onBrowserUnavailable);
     });
   }