fix(terminal): split-terminal visibility

Ref: eclipse-theia/theia#12626/
Signed-off-by: dankeboy36 <dankeboy36@gmail.com>

arduino-ide-extension/src/browser/arduino-ide-frontend-module.ts

@@ -357,6 +357,8 @@ import { MonacoEditorMenuContribution as TheiaMonacoEditorMenuContribution } fro
 import { UpdateArduinoState } from './contributions/update-arduino-state';
 import { TerminalWidgetImpl } from './theia/terminal/terminal-widget-impl';
 import { TerminalWidget } from '@theia/terminal/lib/browser/base/terminal-widget';
+import { TerminalFrontendContribution } from './theia/terminal/terminal-frontend-contribution';
+import { TerminalFrontendContribution as TheiaTerminalFrontendContribution } from '@theia/terminal/lib/browser/terminal-frontend-contribution'
 
 // Hack to fix copy/cut/paste issue after electron version update in Theia.
 // https://github.com/eclipse-theia/theia/issues/12487
@@ -1031,4 +1033,6 @@ export default new ContainerModule((bind, unbind, isBound, rebind) => {
 
   // Patch terminal issues.
   rebind(TerminalWidget).to(TerminalWidgetImpl).inTransientScope();
+  bind(TerminalFrontendContribution).toSelf().inSingletonScope();
+  rebind(TheiaTerminalFrontendContribution).toService(TerminalFrontendContribution);
 });

arduino-ide-extension/src/browser/theia/terminal/terminal-frontend-contribution.ts

@@ -0,0 +1,32 @@
+import { CommandRegistry } from '@theia/core/lib/common/command';
+import { Widget } from '@theia/core/shared/@phosphor/widgets';
+import { injectable } from '@theia/core/shared/inversify';
+import { TerminalWidget } from '@theia/terminal/lib/browser/base/terminal-widget';
+import {
+  TerminalFrontendContribution as TheiaTerminalFrontendContribution,
+  TerminalCommands,
+} from '@theia/terminal/lib/browser/terminal-frontend-contribution';
+
+// Patch for https://github.com/eclipse-theia/theia/pull/12626
+@injectable()
+export class TerminalFrontendContribution extends TheiaTerminalFrontendContribution {
+  override registerCommands(commands: CommandRegistry): void {
+    super.registerCommands(commands);
+    commands.unregisterCommand(TerminalCommands.SPLIT);
+    commands.registerCommand(TerminalCommands.SPLIT, {
+      execute: () => this.splitTerminal(),
+      isEnabled: (w) => this.withWidget(w, () => true),
+      isVisible: (w) => this.withWidget(w, () => true),
+    });
+  }
+
+  private withWidget<T>(
+    widget: Widget | undefined,
+    fn: (widget: TerminalWidget) => T
+  ): T | false {
+    if (widget instanceof TerminalWidget) {
+      return fn(widget);
+    }
+    return false;
+  }
+}