Did some cleanup in prep for next round of changes: Renamed vfs.ts to fileSystem.ts and VirtualFileSystem to FileSystem for consistency and clarity. Added more comments. Removed extraneous "event" parameter from createFileSystemWatcher interface.

server/src/analyzer/importResolver.ts

@@ -9,6 +9,7 @@
  */
 
 import { ConfigOptions, ExecutionEnvironment } from '../common/configOptions';
+import { FileSystem } from '../common/fileSystem';
 import {
     combinePaths,
     ensureTrailingDirectorySeparator,
@@ -23,7 +24,6 @@ import {
 } from '../common/pathUtils';
 import { versionToString } from '../common/pythonVersion';
 import * as StringUtils from '../common/stringUtils';
-import { VirtualFileSystem } from '../common/vfs';
 import { ImplicitImport, ImportResult, ImportType } from './importResult';
 import * as PythonPathUtils from './pythonPathUtils';
 import { isDunderName } from './symbolNameUtils';
@@ -49,9 +49,9 @@ export class ImportResolver {
     private _cachedTypeshedStdLibPath: string | undefined;
     private _cachedTypeshedThirdPartyPath: string | undefined;
 
-    readonly fileSystem: VirtualFileSystem;
+    readonly fileSystem: FileSystem;
 
-    constructor(fs: VirtualFileSystem, configOptions: ConfigOptions) {
+    constructor(fs: FileSystem, configOptions: ConfigOptions) {
         this.fileSystem = fs;
         this._configOptions = configOptions;
     }
@@ -1020,4 +1020,4 @@ export class ImportResolver {
     }
 }
 
-export type ImportResolverFactory = (fs: VirtualFileSystem, options: ConfigOptions) => ImportResolver;
+export type ImportResolverFactory = (fs: FileSystem, options: ConfigOptions) => ImportResolver;

server/src/analyzer/pythonPathUtils.ts

@@ -10,6 +10,7 @@
 import * as child_process from 'child_process';
 
 import { ConfigOptions } from '../common/configOptions';
+import { FileSystem } from '../common/fileSystem';
 import * as pathConsts from '../common/pathConsts';
 import {
     combinePaths,
@@ -20,11 +21,10 @@ import {
     isDirectory,
     normalizePath
 } from '../common/pathUtils';
-import { VirtualFileSystem } from '../common/vfs';
 
 const cachedSearchPaths = new Map<string, PythonPathResult>();
 
-export function getTypeShedFallbackPath(fs: VirtualFileSystem) {
+export function getTypeShedFallbackPath(fs: FileSystem) {
     let moduleDirectory = fs.getModulePath();
     if (!moduleDirectory) {
         return undefined;
@@ -52,7 +52,7 @@ export function getTypeshedSubdirectory(typeshedPath: string, isStdLib: boolean)
 }
 
 export function findPythonSearchPaths(
-    fs: VirtualFileSystem,
+    fs: FileSystem,
     configOptions: ConfigOptions,
     venv: string | undefined,
     importFailureInfo: string[],
@@ -135,7 +135,7 @@ interface PythonPathResult {
 }
 
 export function getPythonPathFromPythonInterpreter(
-    fs: VirtualFileSystem,
+    fs: FileSystem,
     interpreterPath: string | undefined,
     importFailureInfo: string[]
 ): PythonPathResult {

server/src/analyzer/service.ts

@@ -25,6 +25,7 @@ import { Diagnostic } from '../common/diagnostic';
 import { FileDiagnostics } from '../common/diagnosticSink';
 import { FileEditAction, TextEditAction } from '../common/editAction';
 import { LanguageServiceExtension } from '../common/extensibility';
+import { FileSystem, FileWatcher } from '../common/fileSystem';
 import {
     combinePaths,
     FileSpec,
@@ -39,7 +40,6 @@ import {
 } from '../common/pathUtils';
 import { DocumentRange, Position, Range } from '../common/textRange';
 import { Duration, timingStats } from '../common/timing';
-import { FileWatcher, VirtualFileSystem } from '../common/vfs';
 import { HoverResults } from '../languageService/hoverProvider';
 import { SignatureHelpResults } from '../languageService/signatureHelpProvider';
 import { ImportedModuleDescriptor, ImportResolver, ImportResolverFactory } from './importResolver';
@@ -94,7 +94,7 @@ export class AnalyzerService {
 
     constructor(
         instanceName: string,
-        fs: VirtualFileSystem,
+        fs: FileSystem,
         console?: ConsoleInterface,
         importResolverFactory?: ImportResolverFactory,
         configOptions?: ConfigOptions,
@@ -129,7 +129,7 @@ export class AnalyzerService {
         this._clearLibraryReanalysisTimer();
     }
 
-    static createImportResolver(fs: VirtualFileSystem, options: ConfigOptions): ImportResolver {
+    static createImportResolver(fs: FileSystem, options: ConfigOptions): ImportResolver {
         return new ImportResolver(fs, options);
     }
 
@@ -864,7 +864,7 @@ export class AnalyzerService {
                     this._console.log(`Adding fs watcher for directories:\n ${fileList.join('\n')}`);
                 }
 
-                this._sourceFileWatcher = this._fs.createFileSystemWatcher(fileList, 'all', (event, path) => {
+                this._sourceFileWatcher = this._fs.createFileSystemWatcher(fileList, (event, path) => {
                     if (this._verboseOutput) {
                         this._console.log(`Received fs event '${event}' for path '${path}'`);
                     }
@@ -901,7 +901,7 @@ export class AnalyzerService {
             return;
         }
 
-        // watch the library paths for package install/uninstall
+        // Watch the library paths for package install/uninstall
         const importFailureInfo: string[] = [];
         const watchList = findPythonSearchPaths(
             this._fs,
@@ -967,7 +967,7 @@ export class AnalyzerService {
         this._removeConfigFileWatcher();
 
         if (this._configFilePath) {
-            this._configFileWatcher = this._fs.createFileSystemWatcher([this._configFilePath], 'all', event => {
+            this._configFileWatcher = this._fs.createFileSystemWatcher([this._configFilePath], event => {
                 if (this._verboseOutput) {
                     this._console.log(`Received fs event '${event}' for config file`);
                 }

server/src/analyzer/sourceFile.ts

@@ -22,12 +22,12 @@ import { assert } from '../common/debug';
 import { Diagnostic, DiagnosticCategory } from '../common/diagnostic';
 import { DiagnosticSink, TextRangeDiagnosticSink } from '../common/diagnosticSink';
 import { TextEditAction } from '../common/editAction';
+import { FileSystem } from '../common/fileSystem';
 import { getFileName, normalizeSlashes } from '../common/pathUtils';
 import * as StringUtils from '../common/stringUtils';
 import { DocumentRange, getEmptyRange, Position, TextRange } from '../common/textRange';
 import { TextRangeCollection } from '../common/textRangeCollection';
 import { timingStats } from '../common/timing';
-import { VirtualFileSystem } from '../common/vfs';
 import { CompletionItemData, CompletionProvider, ModuleSymbolMap } from '../languageService/completionProvider';
 import { DefinitionProvider } from '../languageService/definitionProvider';
 import { DocumentSymbolProvider } from '../languageService/documentSymbolProvider';
@@ -144,10 +144,10 @@ export class SourceFile {
     private _typingModulePath?: string;
     private _collectionsModulePath?: string;
 
-    readonly fileSystem: VirtualFileSystem;
+    readonly fileSystem: FileSystem;
 
     constructor(
-        fs: VirtualFileSystem,
+        fs: FileSystem,
         filePath: string,
         isTypeshedStubFile: boolean,
         isThirdPartyImport: boolean,

server/src/common/configOptions.ts

@@ -12,9 +12,9 @@ import { isAbsolute } from 'path';
 import * as pathConsts from '../common/pathConsts';
 import { ConsoleInterface } from './console';
 import { DiagnosticRule } from './diagnosticRules';
+import { FileSystem } from './fileSystem';
 import { combinePaths, ensureTrailingDirectorySeparator, FileSpec, getFileSpec, normalizePath } from './pathUtils';
 import { latestStablePythonVersion, PythonVersion, versionFromString } from './pythonVersion';
-import { VirtualFileSystem } from './vfs';
 
 export class ExecutionEnvironment {
     // Default to "." which indicates every file in the project.
@@ -423,7 +423,7 @@ export class ConfigOptions {
         return execEnv;
     }
 
-    addExecEnvironmentForAutoSearchPaths(fs: VirtualFileSystem) {
+    addExecEnvironmentForAutoSearchPaths(fs: FileSystem) {
         // Auto-detect the common scenario where the sources are under the src folder
         const srcPath = combinePaths(this.projectRoot, pathConsts.src);
         if (fs.existsSync(srcPath) && !fs.existsSync(combinePaths(srcPath, '__init__.py'))) {

server/src/common/fileSystem.ts

@@ -1,10 +1,11 @@
 /*
- * vfs.ts
+ * fileSystem.ts
  * Copyright (c) Microsoft Corporation.
  * Licensed under the MIT license.
  *
- * Defines virtual file system interface that our code will operate upon and
- * factory method to expose real file system as virtual file system
+ * Defines a "file system provider" abstraction used throughout the
+ * code base. This abstraction allows us to swap out a real file system
+ * implementation for a virtual (mocked) implementation for testing.
  */
 
 /* eslint-disable no-dupe-class-members */
@@ -15,7 +16,7 @@ import * as fs from 'fs';
 
 import { ConsoleInterface, NullConsole } from './console';
 
-export type Listener = (
+export type FileWatcherEventHandler = (
     eventName: 'add' | 'addDir' | 'change' | 'unlink' | 'unlinkDir',
     path: string,
     stats?: Stats
@@ -37,7 +38,7 @@ export interface Stats {
     isSocket(): boolean;
 }
 
-export interface VirtualFileSystem {
+export interface FileSystem {
     existsSync(path: string): boolean;
     mkdirSync(path: string): void;
     chdir(path: string): void;
@@ -55,15 +56,11 @@ export interface VirtualFileSystem {
         recursive?: boolean,
         listener?: (event: string, filename: string) => void
     ): FileWatcher;
-    createFileSystemWatcher(paths: string[], event: 'all', listener: Listener): FileWatcher;
+    createFileSystemWatcher(paths: string[], listener: FileWatcherEventHandler): FileWatcher;
 }
 
-/**
- * expose real file system as virtual file system
- * @param console console to log messages
- */
-export function createFromRealFileSystem(console?: ConsoleInterface): VirtualFileSystem {
-    return new FileSystem(console ?? new NullConsole());
+export function createFromRealFileSystem(console?: ConsoleInterface): FileSystem {
+    return new RealFileSystem(console ?? new NullConsole());
 }
 
 const _isMacintosh = process.platform === 'darwin';
@@ -77,30 +74,36 @@ class LowLevelWatcher implements FileWatcher {
     }
 }
 
-class FileSystem implements VirtualFileSystem {
+class RealFileSystem implements FileSystem {
     constructor(private _console: ConsoleInterface) {}
 
     existsSync(path: string) {
         return fs.existsSync(path);
     }
+
     mkdirSync(path: string) {
         fs.mkdirSync(path);
     }
+
     chdir(path: string) {
         process.chdir(path);
     }
+
     readdirSync(path: string) {
         return fs.readdirSync(path);
     }
+
     readFileSync(path: string, encoding?: null): Buffer;
     readFileSync(path: string, encoding: string): string;
     readFileSync(path: string, encoding?: string | null): Buffer | string;
     readFileSync(path: string, encoding: string | null = null) {
         return fs.readFileSync(path, { encoding });
     }
+
     writeFileSync(path: string, data: string | Buffer, encoding: string | null) {
         fs.writeFileSync(path, data, { encoding });
     }
+
     statSync(path: string) {
         return fs.statSync(path);
     }
@@ -130,8 +133,8 @@ class FileSystem implements VirtualFileSystem {
         return new LowLevelWatcher(paths);
     }
 
-    createFileSystemWatcher(paths: string[], event: 'all', listener: Listener): FileWatcher {
-        return this._createBaseFileSystemWatcher(paths).on(event, listener);
+    createFileSystemWatcher(paths: string[], listener: FileWatcherEventHandler): FileWatcher {
+        return this._createBaseFileSystemWatcher(paths).on('all', listener);
     }
 
     private _createBaseFileSystemWatcher(paths: string[]): chokidar.FSWatcher {

server/src/common/pathUtils.ts

@@ -14,6 +14,7 @@ import { URI } from 'vscode-uri';
 import { some } from './collectionUtils';
 import { compareValues, Comparison, GetCanonicalFileName, identity } from './core';
 import * as debug from './debug';
+import { FileSystem } from './fileSystem';
 import {
     compareStringsCaseInsensitive,
     compareStringsCaseSensitive,
@@ -21,7 +22,6 @@ import {
     equateStringsCaseSensitive,
     getStringComparer
 } from './stringUtils';
-import { VirtualFileSystem } from './vfs';
 
 export interface FileSpec {
     // File specs can contain wildcard characters (**, *, ?). This
@@ -153,7 +153,7 @@ export function getRelativePath(dirPath: string, relativeTo: string) {
 }
 
 // Creates a directory hierarchy for a path, starting from some ancestor path.
-export function makeDirectories(fs: VirtualFileSystem, dirPath: string, startingFromDirPath: string) {
+export function makeDirectories(fs: FileSystem, dirPath: string, startingFromDirPath: string) {
     if (!dirPath.startsWith(startingFromDirPath)) {
         return;
     }
@@ -170,7 +170,7 @@ export function makeDirectories(fs: VirtualFileSystem, dirPath: string, starting
     }
 }
 
-export function getFileSize(fs: VirtualFileSystem, path: string) {
+export function getFileSize(fs: FileSystem, path: string) {
     try {
         const stat = fs.statSync(path);
         if (stat.isFile()) {
@@ -182,11 +182,11 @@ export function getFileSize(fs: VirtualFileSystem, path: string) {
     return 0;
 }
 
-export function fileExists(fs: VirtualFileSystem, path: string): boolean {
+export function fileExists(fs: FileSystem, path: string): boolean {
     return fileSystemEntryExists(fs, path, FileSystemEntryKind.File);
 }
 
-export function directoryExists(fs: VirtualFileSystem, path: string): boolean {
+export function directoryExists(fs: FileSystem, path: string): boolean {
     return fileSystemEntryExists(fs, path, FileSystemEntryKind.Directory);
 }
 
@@ -317,12 +317,12 @@ export function changeAnyExtension(
     extensions?: string | readonly string[],
     ignoreCase?: boolean
 ): string {
-    const pathext =
+    const pathExt =
         extensions !== undefined && ignoreCase !== undefined
             ? getAnyExtensionFromPath(path, extensions, ignoreCase)
             : getAnyExtensionFromPath(path);
 
-    return pathext ? path.slice(0, path.length - pathext.length) + (ext.startsWith('.') ? ext : '.' + ext) : path;
+    return pathExt ? path.slice(0, path.length - pathExt.length) + (ext.startsWith('.') ? ext : '.' + ext) : path;
 }
 
 /**
@@ -374,7 +374,7 @@ export function getAnyExtensionFromPath(
 
 /**
  * Returns the path except for its containing directory name.
- * Semantics align with NodeJS's `path.basename` except that we support URL's as well.
+ * Semantics align with NodeJS's `path.basename` except that we support URLs as well.
  *
  * ```ts
  * // POSIX
@@ -391,7 +391,7 @@ export function getAnyExtensionFromPath(
 export function getBaseFileName(pathString: string): string;
 /**
  * Gets the portion of a path following the last (non-terminal) separator (`/`).
- * Semantics align with NodeJS's `path.basename` except that we support URL's as well.
+ * Semantics align with NodeJS's `path.basename` except that we support URLs as well.
  * If the base name has any one of the provided extensions, it is removed.
  *
  * ```ts
@@ -516,7 +516,7 @@ export function normalizePath(pathString: string): string {
     return normalizeSlashes(path.normalize(pathString));
 }
 
-export function isDirectory(fs: VirtualFileSystem, path: string): boolean {
+export function isDirectory(fs: FileSystem, path: string): boolean {
     let stat: any;
     try {
         stat = fs.statSync(path);
@@ -527,7 +527,7 @@ export function isDirectory(fs: VirtualFileSystem, path: string): boolean {
     return stat.isDirectory();
 }
 
-export function isFile(fs: VirtualFileSystem, path: string): boolean {
+export function isFile(fs: FileSystem, path: string): boolean {
     let stat: any;
     try {
         stat = fs.statSync(path);
@@ -538,7 +538,7 @@ export function isFile(fs: VirtualFileSystem, path: string): boolean {
     return stat.isFile();
 }
 
-export function getFileSystemEntries(fs: VirtualFileSystem, path: string): FileSystemEntries {
+export function getFileSystemEntries(fs: FileSystem, path: string): FileSystemEntries {
     try {
         const entries = fs.readdirSync(path || '.').sort();
         const files: string[] = [];
@@ -810,7 +810,7 @@ const enum FileSystemEntryKind {
     Directory
 }
 
-function fileSystemEntryExists(fs: VirtualFileSystem, path: string, entryKind: FileSystemEntryKind): boolean {
+function fileSystemEntryExists(fs: FileSystem, path: string, entryKind: FileSystemEntryKind): boolean {
     try {
         const stat = fs.statSync(path);
         switch (entryKind) {

server/src/languageServerBase.ts

@@ -2,6 +2,9 @@
  * languageServerBase.ts
  *
  * Implements common language server functionality.
+ * This is split out as a base class to allow for
+ * different language server variants to be created
+ * from the same core functionality.
  */
 
 import './common/extensions';
@@ -42,9 +45,9 @@ import { ConfigOptions } from './common/configOptions';
 import { ConsoleInterface } from './common/console';
 import { Diagnostic as AnalyzerDiagnostic, DiagnosticCategory } from './common/diagnostic';
 import { LanguageServiceExtension } from './common/extensibility';
+import { createFromRealFileSystem, FileSystem } from './common/fileSystem';
 import { convertPathToUri, convertUriToPath } from './common/pathUtils';
 import { Position } from './common/textRange';
-import { createFromRealFileSystem, VirtualFileSystem } from './common/vfs';
 import { AnalyzerServiceExecutor } from './languageService/analyzerServiceExecutor';
 import { CompletionItemData } from './languageService/completionProvider';
 import { convertHoverResults } from './languageService/hoverProvider';
@@ -84,7 +87,7 @@ export interface LanguageServerInterface {
     readonly rootPath: string;
     readonly console: ConsoleInterface;
     readonly window: WindowInterface;
-    readonly fs: VirtualFileSystem;
+    readonly fs: FileSystem;
 }
 
 export abstract class LanguageServerBase implements LanguageServerInterface {
@@ -101,7 +104,7 @@ export abstract class LanguageServerBase implements LanguageServerInterface {
     rootPath = '';
 
     // File system abstraction.
-    fs: VirtualFileSystem;
+    fs: FileSystem;
 
     constructor(private _productName: string, rootDirectory: string, private _extension?: LanguageServiceExtension) {
         this._connection.console.log(`${_productName} language server starting`);
@@ -146,7 +149,7 @@ export abstract class LanguageServerBase implements LanguageServerInterface {
         return undefined;
     }
 
-    protected createImportResolver(fs: VirtualFileSystem, options: ConfigOptions): ImportResolver {
+    protected createImportResolver(fs: FileSystem, options: ConfigOptions): ImportResolver {
         return new ImportResolver(fs, options);
     }
 

server/src/pyright.ts

@@ -25,7 +25,7 @@ import { DiagnosticCategory } from './common/diagnostic';
 import { FileDiagnostics } from './common/diagnosticSink';
 import { combinePaths, normalizePath } from './common/pathUtils';
 import { Range } from './common/textRange';
-import { createFromRealFileSystem } from './common/vfs';
+import { createFromRealFileSystem } from './common/fileSystem';
 
 const toolName = 'pyright';
 

server/src/tests/config.test.ts

@@ -13,8 +13,8 @@ import { AnalyzerService } from '../analyzer/service';
 import { CommandLineOptions } from '../common/commandLineOptions';
 import { ConfigOptions, ExecutionEnvironment } from '../common/configOptions';
 import { NullConsole } from '../common/console';
+import { createFromRealFileSystem } from '../common/fileSystem';
 import { combinePaths, getBaseFileName, normalizePath, normalizeSlashes } from '../common/pathUtils';
-import { createFromRealFileSystem } from '../common/vfs';
 
 test('FindFilesWithConfigFile', () => {
     const cwd = normalizePath(combinePaths(process.cwd(), '../server'));

server/src/tests/harness/fourslash/testLanguageService.ts

@@ -3,14 +3,14 @@
  * Copyright (c) Microsoft Corporation.
  * Licensed under the MIT license.
  *
- * test mock that implements LanguageServiceInterface
+ * Test mock that implements LanguageServiceInterface
  */
 
 import * as path from 'path';
 
 import { ConsoleInterface } from '../../../common/console';
 import * as debug from '../../../common/debug';
-import { VirtualFileSystem } from '../../../common/vfs';
+import { FileSystem } from '../../../common/fileSystem';
 import {
     LanguageServerInterface,
     ServerSettings,
@@ -21,11 +21,7 @@ import {
 export class TestLanguageService implements LanguageServerInterface {
     private readonly _workspace: WorkspaceServiceInstance;
 
-    constructor(
-        workspace: WorkspaceServiceInstance,
-        readonly console: ConsoleInterface,
-        readonly fs: VirtualFileSystem
-    ) {
+    constructor(workspace: WorkspaceServiceInstance, readonly console: ConsoleInterface, readonly fs: FileSystem) {
         this._workspace = workspace;
     }
 

server/src/tests/harness/host.ts

@@ -8,6 +8,7 @@ import * as os from 'os';
 import * as pathModule from 'path';
 
 import { NullConsole } from '../../common/console';
+import { createFromRealFileSystem } from '../../common/fileSystem';
 import {
     combinePaths,
     directoryExists,
@@ -17,7 +18,6 @@ import {
     resolvePaths
 } from '../../common/pathUtils';
 import { compareStringsCaseInsensitive, compareStringsCaseSensitive } from '../../common/stringUtils';
-import { createFromRealFileSystem } from '../../common/vfs';
 
 export const HOST: TestHost = createHost();
 

server/src/tests/harness/vfs/filesystem.ts

@@ -7,8 +7,8 @@
  */
 
 /* eslint-disable no-dupe-class-members */
+import { FileWatcher, FileWatcherEventHandler } from '../../../common/fileSystem';
 import * as pathUtil from '../../../common/pathUtils';
-import { FileWatcher, Listener } from '../../../common/vfs';
 import { bufferFrom, createIOError } from '../utils';
 import { closeIterator, getIterator, Metadata, nextResult, SortedMap } from './../utils';
 import { validate, ValidationFlags } from './pathValidation';
@@ -305,7 +305,7 @@ export class FileSystem {
         return results;
     }
 
-    createFileSystemWatcher(paths: string[], event: 'all', listener: Listener): FileWatcher {
+    createFileSystemWatcher(paths: string[], listener: FileWatcherEventHandler): FileWatcher {
         return {
             close: () => {
                 /* left empty */

server/src/tests/sourceFile.test.ts

@@ -10,8 +10,8 @@
 import { ImportResolver } from '../analyzer/importResolver';
 import { SourceFile } from '../analyzer/sourceFile';
 import { ConfigOptions } from '../common/configOptions';
+import { createFromRealFileSystem } from '../common/fileSystem';
 import { combinePaths } from '../common/pathUtils';
-import { createFromRealFileSystem } from '../common/vfs';
 
 test('Empty', () => {
     const filePath = combinePaths(process.cwd(), 'tests/samples/test_file1.py');

server/src/tests/testUtils.ts

@@ -19,7 +19,7 @@ import { cloneDiagnosticSettings, ConfigOptions, ExecutionEnvironment } from '..
 import { fail } from '../common/debug';
 import { Diagnostic, DiagnosticCategory } from '../common/diagnostic';
 import { DiagnosticSink, TextRangeDiagnosticSink } from '../common/diagnosticSink';
-import { createFromRealFileSystem } from '../common/vfs';
+import { createFromRealFileSystem } from '../common/fileSystem';
 import { ParseOptions, Parser, ParseResults } from '../parser/parser';
 
 // This is a bit gross, but it's necessary to allow the fallback typeshed