turning highlighted Markdown text to link to pasted URL (#185924)

* turning highlighted Mardown text to link to pasted URL

* resolved comments

* resolved more comments

* preserved behavior of existing file pasting logic

---------

Co-authored-by: Meghan Kulkarni <t-mekulkarni@microsoft.com>

extensions/markdown-language-features/src/languageFeatures/copyFiles/copyPasteLinks.ts

@@ -0,0 +1,53 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as vscode from 'vscode';
+import { getMarkdownLink } from './shared';
+
+class PasteLinkEditProvider implements vscode.DocumentPasteEditProvider {
+
+	private readonly _id = 'insertMarkdownLink';
+	async provideDocumentPasteEdits(
+		document: vscode.TextDocument,
+		ranges: readonly vscode.Range[],
+		dataTransfer: vscode.DataTransfer,
+		token: vscode.CancellationToken,
+	): Promise<vscode.DocumentPasteEdit | undefined> {
+		const enabled = vscode.workspace.getConfiguration('markdown', document).get('editor.pasteUrlAsFormattedLink.enabled', true);
+		if (!enabled) {
+			return;
+		}
+
+		// Check if dataTransfer contains a URL
+		const item = dataTransfer.get('text/plain');
+		try {
+			new URL(await item?.value);
+		} catch (error) {
+			return;
+		}
+
+		const label = vscode.l10n.t('Insert Markdown Link');
+		const uriEdit = new vscode.DocumentPasteEdit('', this._id, label);
+		const urlList = await item?.asString();
+		if (!urlList) {
+			return undefined;
+		}
+		const pasteEdit = await getMarkdownLink(document, ranges, urlList, token);
+		if (!pasteEdit) {
+			return;
+		}
+
+		uriEdit.additionalEdit = pasteEdit.additionalEdits;
+		return uriEdit;
+	}
+}
+
+export function registerLinkPasteSupport(selector: vscode.DocumentSelector,) {
+	return vscode.languages.registerDocumentPasteEditProvider(selector, new PasteLinkEditProvider(), {
+		pasteMimeTypes: [
+			'text/plain',
+		]
+	});
+}