Only allow a single model editor per database

This will add checks in the appropriate places to ensure that only a
single model editor is opened per database.

extensions/ql-vscode/src/model-editor/model-editor-module.ts

@@ -128,6 +128,15 @@ export class ModelEditorModule extends DisposableObject {
         return;
       }
 
+      const existingViews = this.editorViewTracker.getViews(
+        db.databaseUri.toString(),
+      );
+      if (existingViews.length > 0) {
+        await Promise.all(existingViews.map((view) => view.focusView()));
+
+        return;
+      }
+
       return withProgress(
         async (progress) => {
           const maxStep = 4;
@@ -192,6 +201,17 @@ export class ModelEditorModule extends DisposableObject {
             maxStep,
           });
 
+          // Check again just before opening the editor to ensure no model editor has been opened between
+          // our first check and now.
+          const existingViews = this.editorViewTracker.getViews(
+            db.databaseUri.toString(),
+          );
+          if (existingViews.length > 0) {
+            await Promise.all(existingViews.map((view) => view.focusView()));
+
+            return;
+          }
+
           const view = new ModelEditorView(
             this.app,
             this.modelingStore,

extensions/ql-vscode/src/model-editor/model-editor-view.ts

@@ -352,6 +352,10 @@ export class ModelEditorView extends AbstractWebview<
     return this.databaseItem.databaseUri.toString();
   }
 
+  public async focusView(): Promise<void> {
+    this.panel?.reveal();
+  }
+
   public async revealMethod(method: Method): Promise<void> {
     this.panel?.reveal();
 
@@ -520,6 +524,15 @@ export class ModelEditorView extends AbstractWebview<
         return;
       }
 
+      let existingViews = this.viewTracker.getViews(
+        addedDatabase.databaseUri.toString(),
+      );
+      if (existingViews.length > 0) {
+        await Promise.all(existingViews.map((view) => view.focusView()));
+
+        return;
+      }
+
       const modelFile = await pickExtensionPack(
         this.cliServer,
         addedDatabase,
@@ -532,6 +545,17 @@ export class ModelEditorView extends AbstractWebview<
         return;
       }
 
+      // Check again just before opening the editor to ensure no model editor has been opened between
+      // our first check and now.
+      existingViews = this.viewTracker.getViews(
+        addedDatabase.databaseUri.toString(),
+      );
+      if (existingViews.length > 0) {
+        await Promise.all(existingViews.map((view) => view.focusView()));
+
+        return;
+      }
+
       const view = new ModelEditorView(
         this.app,
         this.modelingStore,