Support notebook file types contribution (#3196)

* Support notebook file types contribution
- Extensions can define a provider and what file types it should be used for
- Verified that this works for Jupyter Content & Server Managers.
- Starts Jupyter server as expected

Not in this PR:
- Support for session manager end to end
- Tests

src/sql/services/notebook/notebookRegistry.ts

@@ -0,0 +1,116 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+'use strict';
+
+import { IJSONSchema } from 'vs/base/common/jsonSchema';
+import { ExtensionsRegistry, IExtensionPointUser } from 'vs/workbench/services/extensions/common/extensionsRegistry';
+import { localize } from 'vs/nls';
+import * as platform from 'vs/platform/registry/common/platform';
+
+export const Extensions = {
+	NotebookProviderContribution: 'notebook.providers'
+};
+
+export interface NotebookProviderDescription {
+	provider: string;
+	fileExtensions: string | string[];
+}
+
+let notebookProviderType: IJSONSchema = {
+	type: 'object',
+	default: { provider: '', fileExtensions: [] },
+	properties: {
+		provider: {
+			description: localize('carbon.extension.contributes.notebook.provider', 'Identifier of the notebook provider.'),
+			type: 'string'
+		},
+		fileExtensions: {
+			description: localize('carbon.extension.contributes.notebook.fileExtensions', 'What file extensions should be registered to this notebook provider'),
+			oneOf: [
+				{ type: 'string' },
+				{
+					type: 'array',
+					items: {
+						type: 'string'
+					}
+				}
+			]
+		}
+	}
+};
+
+let notebookContrib: IJSONSchema = {
+	description: localize('vscode.extension.contributes.notebook.providers', "Contributes notebook providers."),
+	oneOf: [
+		notebookProviderType,
+		{
+			type: 'array',
+			items: notebookProviderType
+		}
+	]
+};
+
+export interface INotebookProviderRegistry {
+	registerNotebookProvider(provider: NotebookProviderDescription): void;
+	getSupportedFileExtensions(): string[];
+	getProviderForFileType(fileType: string): string;
+}
+
+class NotebookProviderRegistry implements INotebookProviderRegistry {
+	private providerIdToProviders = new Map<string, NotebookProviderDescription>();
+	private fileToProviders = new Map<string, NotebookProviderDescription>();
+
+	registerNotebookProvider(provider: NotebookProviderDescription): void {
+		// Note: this method intentionally overrides default provider for a file type.
+		// This means that any built-in provider will be overridden by registered extensions
+		this.providerIdToProviders.set(provider.provider, provider);
+		if (provider.fileExtensions) {
+			if (Array.isArray<string>(provider.fileExtensions)) {
+				for (let fileType of provider.fileExtensions) {
+					this.addFileProvider(fileType, provider);
+				}
+			} else {
+				this.addFileProvider(provider.fileExtensions, provider);
+			}
+		}
+	}
+
+	private addFileProvider(fileType: string, provider: NotebookProviderDescription) {
+		this.fileToProviders.set(fileType.toUpperCase(), provider);
+	}
+
+	getSupportedFileExtensions(): string[] {
+		return Array.from(this.fileToProviders.keys());
+	}
+
+	getProviderForFileType(fileType: string): string {
+		fileType = fileType.toUpperCase();
+		let provider = this.fileToProviders.get(fileType);
+		return provider ? provider.provider : undefined;
+	}
+}
+
+const notebookProviderRegistry = new NotebookProviderRegistry();
+platform.Registry.add(Extensions.NotebookProviderContribution, notebookProviderRegistry);
+
+
+ExtensionsRegistry.registerExtensionPoint<NotebookProviderDescription | NotebookProviderDescription[]>(Extensions.NotebookProviderContribution, [], notebookContrib).setHandler(extensions => {
+
+	function handleExtension(contrib: NotebookProviderDescription, extension: IExtensionPointUser<any>) {
+		notebookProviderRegistry.registerNotebookProvider(contrib);
+	}
+
+	for (let extension of extensions) {
+		const { value } = extension;
+		if (Array.isArray<NotebookProviderDescription>(value)) {
+			for (let command of value) {
+				handleExtension(command, extension);
+			}
+		} else {
+			handleExtension(value, extension);
+		}
+	}
+});