Re-apply markdown copy files setting (#169661)

* Revert "Revert "Add experimental setting to define where files should be copied for markdown (#169454)" (#169615)"

This reverts commit b2121c2dbe.

* Fix tests

These paths should always use `/`

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

@@ -0,0 +1,88 @@
+/*---------------------------------------------------------------------------------------------
+ *  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 { Schemes } from '../../util/schemes';
+import { getNewFileName } from './copyFiles';
+import { createUriListSnippet, tryGetUriListSnippet } from './dropIntoEditor';
+
+const supportedImageMimes = new Set([
+	'image/png',
+	'image/jpg',
+]);
+
+class PasteEditProvider implements vscode.DocumentPasteEditProvider {
+
+	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('experimental.editor.pasteLinks.enabled', true);
+		if (!enabled) {
+			return;
+		}
+
+		if (document.uri.scheme === Schemes.notebookCell) {
+			return;
+		}
+
+		for (const imageMime of supportedImageMimes) {
+			const file = dataTransfer.get(imageMime)?.asFile();
+			if (file) {
+				const edit = await this._makeCreateImagePasteEdit(document, file, token);
+				if (token.isCancellationRequested) {
+					return;
+				}
+
+				if (edit) {
+					return edit;
+				}
+			}
+		}
+
+		const snippet = await tryGetUriListSnippet(document, dataTransfer, token);
+		return snippet ? new vscode.DocumentPasteEdit(snippet) : undefined;
+	}
+
+	private async _makeCreateImagePasteEdit(document: vscode.TextDocument, file: vscode.DataTransferFile, token: vscode.CancellationToken): Promise<vscode.DocumentPasteEdit | undefined> {
+		if (file.uri) {
+			// If file is already in workspace, we don't want to create a copy of it
+			const workspaceFolder = vscode.workspace.getWorkspaceFolder(file.uri);
+			if (workspaceFolder) {
+				const snippet = createUriListSnippet(document, [file.uri]);
+				return snippet ? new vscode.DocumentPasteEdit(snippet) : undefined;
+			}
+		}
+
+		const uri = await getNewFileName(document, file);
+		if (token.isCancellationRequested) {
+			return;
+		}
+
+		const snippet = createUriListSnippet(document, [uri]);
+		if (!snippet) {
+			return;
+		}
+
+		// Note that there is currently no way to undo the file creation :/
+		const workspaceEdit = new vscode.WorkspaceEdit();
+		workspaceEdit.createFile(uri, { contents: await file.data() });
+
+		const pasteEdit = new vscode.DocumentPasteEdit(snippet);
+		pasteEdit.additionalEdit = workspaceEdit;
+		return pasteEdit;
+	}
+}
+
+export function registerPasteSupport(selector: vscode.DocumentSelector,) {
+	return vscode.languages.registerDocumentPasteEditProvider(selector, new PasteEditProvider(), {
+		pasteMimeTypes: [
+			'text/uri-list',
+			...supportedImageMimes,
+		]
+	});
+}