Add support for linking to local files

extension/src/editor.ts

@@ -5,6 +5,9 @@ import { Base64 } from "js-base64";
 import { ExcalidrawDocument } from "./document";
 import { languageMap } from "./lang";
 
+const urlRegex = /^(http[s]?:\/\/)?(www\.)?[a-zA-Z0-9.-]+\.[a-zA-Z]{2,5}\.?/;
+//^ Replace with URL.canParse once it becomes available in VSCode
+
 export class ExcalidrawEditorProvider
   implements vscode.CustomEditorProvider<ExcalidrawDocument>
 {
@@ -163,7 +166,7 @@ export class ExcalidrawEditor {
             await this.document.update(new Uint8Array(msg.content));
             break;
           case "link-open":
-            vscode.env.openExternal(vscode.Uri.parse(msg.url));
+            await this.handleLinkOpen(msg.url);
             break;
           case "error":
             vscode.window.showErrorMessage(msg.content);
@@ -342,6 +345,31 @@ export class ExcalidrawEditor {
     }
   }
 
+  private async handleLinkOpen(url: string) {
+    if (url.match(urlRegex)) {
+      await vscode.env.openExternal(vscode.Uri.parse(url));
+      return;
+    }
+    const targetPath = path.resolve(
+      path.dirname(this.document.uri.fsPath),
+      url
+    );
+    const targetUri = vscode.Uri.file(targetPath);
+
+    if (url.match(/\.excalidraw(\.|$)/)) {
+      await vscode.commands.executeCommand(
+        "vscode.openWith",
+        targetUri,
+        "editor.excalidraw"
+      );
+      return;
+    }
+
+    await vscode.window.showTextDocument(targetUri, {
+      preview: true,
+    });
+  }
+
   private async buildHtmlForWebview(config: any): Promise<string> {
     const publicUri = vscode.Uri.joinPath(this.context.extensionUri, "public");
     const content = await vscode.workspace.fs.readFile(