Try adding support for code mirror printing

packages/apputils/src/printing.ts

@@ -60,7 +60,7 @@ export namespace Printing {
    * to a hidden iframe and printing that iframe.
    */
   export function printWidget(widget: Widget): Promise<void> {
-    return printContent(widget.node);
+    return printElement(widget.node);
   }
 
   const settings = ServerConnection.makeSettings();
@@ -79,27 +79,37 @@ export namespace Printing {
   }
 
   /**
-   * Prints a URL or an element in an iframe and then removes the iframe after printing.
+   * Prints an element by copying it into an iframe.
    */
-  async function printContent(textOrEl: string | HTMLElement): Promise<void> {
-    const isText = typeof textOrEl === 'string';
+  export function printElement(el: HTMLElement): Promise<void> {
+    return printContent(parent => parent.appendChild(el.cloneNode(true)));
+  }
+  /**
+   * Prints a URL or an callback that sets a node element in an iframe and then removes the iframe after printing.
+   */
+  export async function printContent(
+    textOrCallback: string | ((el: HTMLElement) => void)
+  ): Promise<void> {
     const iframe = createIFrame();
-
+    let loaded = resolveWhenLoaded(iframe);
     const parent = window.document.body;
     parent.appendChild(iframe);
-    if (isText) {
-      iframe.srcdoc = textOrEl as string;
-      await resolveWhenLoaded(iframe);
+    if (typeof textOrCallback === 'string') {
+      iframe.srcdoc = textOrCallback as string;
     } else {
       iframe.src = 'about:blank';
-      setIFrameNode(iframe, textOrEl as HTMLElement);
+      await loaded;
+      textOrCallback(iframe.contentDocument.body);
+      iframe.contentDocument.close();
     }
+    await loaded;
+    console.log('new new', iframe);
     const printed = resolveAfterEvent();
     launchPrint(iframe.contentWindow);
     // Once the print dialog has been dismissed, we regain event handling,
     // and it should be safe to discard the hidden iframe.
     await printed;
-    parent.removeChild(iframe);
+    // parent.removeChild(iframe);
   }
 
   /**
@@ -125,14 +135,6 @@ export namespace Printing {
     return el;
   }
 
-  /**
-   * Copies a node from the base document to the iframe.
-   */
-  function setIFrameNode(iframe: HTMLIFrameElement, node: HTMLElement) {
-    iframe.contentDocument.body.appendChild(node.cloneNode(true));
-    iframe.contentDocument.close();
-  }
-
   /**
    * Promise that resolves when all resources are loaded in the window.
    */

packages/codemirror/src/editor.ts

@@ -13,7 +13,7 @@ import { IDisposable, DisposableDelegate } from '@phosphor/disposable';
 
 import { Signal } from '@phosphor/signaling';
 
-import { showDialog } from '@jupyterlab/apputils';
+import { showDialog, Printing } from '@jupyterlab/apputils';
 
 import { Poll } from '@jupyterlab/coreutils';
 
@@ -89,7 +89,8 @@ const HOVER_TIMEOUT = 1000;
 /**
  * CodeMirror editor.
  */
-export class CodeMirrorEditor implements CodeEditor.IEditor {
+export class CodeMirrorEditor
+  implements CodeEditor.IEditor, Printing.IPrintable {
   /**
    * Construct a CodeMirror editor.
    */
@@ -173,6 +174,19 @@ export class CodeMirrorEditor implements CodeEditor.IEditor {
     });
   }
 
+  /**
+   * Prints this editor by creating a new one in an iframe.
+   */
+  [Printing.symbol]() {
+    return async () => {
+      Printing.printContent(el => {
+        Private.createEditor(el, this._config)
+          .getDoc()
+          .setValue(this.model.value.text);
+      });
+    };
+  }
+
   /**
    * A signal emitted when either the top or bottom edge is requested.
    */

packages/fileeditor/src/widget.ts

@@ -20,6 +20,7 @@ import {
 import { PromiseDelegate } from '@phosphor/coreutils';
 
 import { Message } from '@phosphor/messaging';
+import { Printing } from '@jupyterlab/apputils';
 
 /**
  * The data attribute added to a widget that can run code.
@@ -156,7 +157,7 @@ export class FileEditorCodeWrapper extends CodeEditorWrapper {
 /**
  * A widget for editors.
  */
-export class FileEditor extends Widget {
+export class FileEditor extends Widget implements Printing.IPrintable {
   /**
    * Construct a new editor widget.
    */
@@ -216,6 +217,13 @@ export class FileEditor extends Widget {
     }
   }
 
+  /**
+   * Delegate printing to code editor widget
+   */
+  [Printing.symbol]() {
+    return Printing.getPrintFunction(this.editorWidget.editor);
+  }
+
   /**
    * Handle `after-attach` messages for the widget.
    */