Add a TextDocumentContentProvider for source-generated files

This allows the Roslyn LSP to return document references with a
roslyn-source-generated URI, and we'll turn around and ask the LSP
for those files when they're opened.

For now we don't worry about refreshing files if they've changed,
just to keep this simple.

Author: jasonmalinowski

src/lsptoolshost/roslynLanguageServer.ts

@@ -74,6 +74,7 @@ import {
     showErrorMessage,
     showInformationMessage,
 } from '../shared/observers/utils/showMessage';
+import { registerSourceGeneratedFilesContentProvider } from './sourceGeneratedFilesContentProvider';
 
 let _channel: vscode.OutputChannel;
 let _traceChannel: vscode.OutputChannel;
@@ -1068,6 +1069,8 @@ export async function activateRoslynLanguageServer(
 
     registerRestoreCommands(context, languageServer, dotnetChannel);
 
+    registerSourceGeneratedFilesContentProvider(context, languageServer);
+
     context.subscriptions.push(registerLanguageServerOptionChanges(optionObservable));
 
     return languageServer;

src/lsptoolshost/roslynProtocol.ts

@@ -230,6 +230,14 @@ export interface CopilotRelatedDocumentsReport {
     _vs_file_paths?: string[];
 }
 
+export interface SourceGeneratorGetRequestParams {
+    textDocument: lsp.TextDocumentIdentifier;
+}
+
+export interface SourceGeneratedDocumentText {
+    text: string;
+}
+
 export namespace WorkspaceDebugConfigurationRequest {
     export const method = 'workspace/debugConfiguration';
     export const messageDirection: lsp.MessageDirection = lsp.MessageDirection.clientToServer;
@@ -351,3 +359,9 @@ export namespace CopilotRelatedDocumentsRequest {
         void
     >(method);
 }
+
+export namespace SourceGeneratorGetTextRequest {
+    export const method = 'sourceGeneratedFile/_roslyn_getText';
+    export const messageDirection: lsp.MessageDirection = lsp.MessageDirection.clientToServer;
+    export const type = new lsp.RequestType<SourceGeneratorGetRequestParams, SourceGeneratedDocumentText, void>(method);
+}

src/lsptoolshost/sourceGeneratedFilesContentProvider.ts

@@ -0,0 +1,31 @@
+/*---------------------------------------------------------------------------------------------
+ *  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 * as RoslynProtocol from './roslynProtocol';
+import { RoslynLanguageServer } from './roslynLanguageServer';
+import { UriConverter } from './uriConverter';
+import * as lsp from 'vscode-languageserver-protocol';
+
+export function registerSourceGeneratedFilesContentProvider(
+    context: vscode.ExtensionContext,
+    languageServer: RoslynLanguageServer
+) {
+    context.subscriptions.push(
+        vscode.workspace.registerTextDocumentContentProvider(
+            'roslyn-source-generated',
+            new (class implements vscode.TextDocumentContentProvider {
+                async provideTextDocumentContent(uri: vscode.Uri, token: vscode.CancellationToken): Promise<string> {
+                    const result = await languageServer.sendRequest(
+                        RoslynProtocol.SourceGeneratorGetTextRequest.type,
+                        { textDocument: lsp.TextDocumentIdentifier.create(UriConverter.serialize(uri)) },
+                        token
+                    );
+                    return result.text;
+                }
+            })()
+        )
+    );
+}