Enable TS strict mode by default (denoland/deno#3899)

Fixes denoland/deno#3324 

Co-authored-by: Kitson Kelly <me@kitsonkelly.com>

encoding/base32_test.ts

@@ -6,7 +6,7 @@ import { encode, decode } from "./base32.ts";
 
 // Lifted from https://stackoverflow.com/questions/38987784
 const fromHexString = (hexString: string): Uint8Array =>
-  new Uint8Array(hexString.match(/.{1,2}/g).map(byte => parseInt(byte, 16)));
+  new Uint8Array(hexString.match(/.{1,2}/g)!.map(byte => parseInt(byte, 16)));
 const toHexString = (bytes: Uint8Array): string =>
   bytes.reduce((str, byte) => str + byte.toString(16).padStart(2, "0"), "");
 

encoding/csv.ts

@@ -46,7 +46,7 @@ function chkOptions(opt: ReadOptions): void {
   }
   if (
     INVALID_RUNE.includes(opt.comma) ||
-    INVALID_RUNE.includes(opt.comment) ||
+    (typeof opt.comment === "string" && INVALID_RUNE.includes(opt.comment)) ||
     opt.comma === opt.comment
   ) {
     throw new Error("Invalid Delimiter");
@@ -122,7 +122,7 @@ export async function readMatrix(
   }
 ): Promise<string[][]> {
   const result: string[][] = [];
-  let _nbFields: number;
+  let _nbFields: number | undefined;
   let lineResult: string[];
   let first = true;
   let lineIndex = 0;
@@ -253,8 +253,10 @@ export async function parse(
     });
   }
   if (opt.parse) {
-    assert(opt.parse != null, "opt.parse must be set");
-    return r.map((e: string[]): unknown => opt.parse(e));
+    return r.map((e: string[]): unknown => {
+      assert(opt.parse, "opt.parse must be set");
+      return opt.parse(e);
+    });
   }
   return r;
 }

encoding/csv_test.ts

@@ -476,26 +476,32 @@ for (const t of testCases) {
       if (t.Error) {
         let err;
         try {
-          actual = await readMatrix(new BufReader(new StringReader(t.Input)), {
-            comma: comma,
-            comment: comment,
-            trimLeadingSpace: trim,
-            fieldsPerRecord: fieldsPerRec,
-            lazyQuotes: lazyquote
-          });
+          actual = await readMatrix(
+            new BufReader(new StringReader(t.Input ?? "")),
+            {
+              comma: comma,
+              comment: comment,
+              trimLeadingSpace: trim,
+              fieldsPerRecord: fieldsPerRec,
+              lazyQuotes: lazyquote
+            }
+          );
         } catch (e) {
           err = e;
         }
         assert(err);
         assertEquals(err.message, t.Error);
       } else {
-        actual = await readMatrix(new BufReader(new StringReader(t.Input)), {
-          comma: comma,
-          comment: comment,
-          trimLeadingSpace: trim,
-          fieldsPerRecord: fieldsPerRec,
-          lazyQuotes: lazyquote
-        });
+        actual = await readMatrix(
+          new BufReader(new StringReader(t.Input ?? "")),
+          {
+            comma: comma,
+            comment: comment,
+            trimLeadingSpace: trim,
+            fieldsPerRecord: fieldsPerRec,
+            lazyQuotes: lazyquote
+          }
+        );
         const expected = t.Output;
         assertEquals(actual, expected);
       }

encoding/yaml/loader/loader.ts

@@ -187,7 +187,7 @@ interface DirectiveHandlers {
   [directive: string]: (
     state: LoaderState,
     name: string,
-    ...args: unknown[]
+    ...args: string[]
   ) => void;
 }
 
@@ -362,7 +362,7 @@ function storeMappingPair(
         mergeMappings(state, result, valueNode[index], overridableKeys);
       }
     } else {
-      mergeMappings(state, result, valueNode, overridableKeys);
+      mergeMappings(state, result, valueNode as ArrayObject, overridableKeys);
     }
   } else {
     if (
@@ -1610,7 +1610,7 @@ function readDocument(state: LoaderState): void {
   const documentStart = state.position;
   let position: number,
     directiveName: string,
-    directiveArgs: unknown[],
+    directiveArgs: string[],
     hasDirectives = false,
     ch: number;
 

examples/gist.ts

@@ -24,7 +24,7 @@ if (parsedArgs._.length === 0) {
   Deno.exit(1);
 }
 
-const files = {};
+const files: Record<string, { content: string }> = {};
 for (const filename of parsedArgs._) {
   const base = pathBase(filename);
   const content = await Deno.readFile(filename);

fs/copy.ts

@@ -85,6 +85,8 @@ async function copyFile(
   await Deno.copyFile(src, dest);
   if (options.preserveTimestamps) {
     const statInfo = await Deno.stat(src);
+    assert(statInfo.accessed != null, `statInfo.accessed is unavailable`);
+    assert(statInfo.modified != null, `statInfo.modified is unavailable`);
     await Deno.utime(dest, statInfo.accessed, statInfo.modified);
   }
 }

fs/empty_dir_test.ts

@@ -1,5 +1,6 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
 import {
+  assert,
   assertEquals,
   assertStrContains,
   assertThrows,
@@ -225,6 +226,8 @@ Deno.test(async function emptyDirPermission(): Promise<void> {
         args: args
       });
 
+      assert(stdout);
+
       const output = await Deno.readAll(stdout);
 
       assertStrContains(new TextDecoder().decode(output), s.output);

fs/exists_test.ts

@@ -131,7 +131,7 @@ Deno.test(async function existsPermission(): Promise<void> {
       args: args
     });
 
-    const output = await Deno.readAll(stdout);
+    const output = await Deno.readAll(stdout!);
 
     assertStrContains(new TextDecoder().decode(output), s.output);
   }

fs/walk.ts

@@ -65,9 +65,9 @@ export async function* walk(
     includeFiles = true,
     includeDirs = true,
     followSymlinks = false,
-    exts = null,
-    match = null,
-    skip = null
+    exts = undefined,
+    match = undefined,
+    skip = undefined
   }: WalkOptions = {}
 ): AsyncIterableIterator<WalkInfo> {
   if (maxDepth < 0) {
@@ -76,7 +76,7 @@ export async function* walk(
   if (includeDirs && include(root, exts, match, skip)) {
     yield { filename: root, info: await stat(root) };
   }
-  if (maxDepth < 1 || !include(root, null, null, skip)) {
+  if (maxDepth < 1 || !include(root, undefined, undefined, skip)) {
     return;
   }
   const ls: FileInfo[] = await readDir(root);
@@ -119,9 +119,9 @@ export function* walkSync(
     includeFiles = true,
     includeDirs = true,
     followSymlinks = false,
-    exts = null,
-    match = null,
-    skip = null
+    exts = undefined,
+    match = undefined,
+    skip = undefined
   }: WalkOptions = {}
 ): IterableIterator<WalkInfo> {
   if (maxDepth < 0) {
@@ -130,7 +130,7 @@ export function* walkSync(
   if (includeDirs && include(root, exts, match, skip)) {
     yield { filename: root, info: statSync(root) };
   }
-  if (maxDepth < 1 || !include(root, null, null, skip)) {
+  if (maxDepth < 1 || !include(root, undefined, undefined, skip)) {
     return;
   }
   const ls: FileInfo[] = readDirSync(root);

http/cookie.ts

@@ -45,7 +45,7 @@ function toString(cookie: Cookie): string {
   if (cookie.httpOnly) {
     out.push("HttpOnly");
   }
-  if (Number.isInteger(cookie.maxAge)) {
+  if (typeof cookie.maxAge === "number" && Number.isInteger(cookie.maxAge)) {
     assert(cookie.maxAge > 0, "Max-Age must be an integer superior to 0");
     out.push(`Max-Age=${cookie.maxAge}`);
   }

http/file_server.ts

@@ -15,6 +15,7 @@ import {
   Response
 } from "./server.ts";
 import { parse } from "../flags/mod.ts";
+import { assert } from "../testing/asserts.ts";
 
 interface EntryInfo {
   mode: string;
@@ -40,10 +41,10 @@ const encoder = new TextEncoder();
 const serverArgs = parse(args) as FileServerArgs;
 
 const CORSEnabled = serverArgs.cors ? true : false;
-const target = posix.resolve(serverArgs._[1] || "");
-const addr = `0.0.0.0:${serverArgs.port || serverArgs.p || 4500}`;
+const target = posix.resolve(serverArgs._[1] ?? "");
+const addr = `0.0.0.0:${serverArgs.port ?? serverArgs.p ?? 4500}`;
 
-if (serverArgs.h || serverArgs.help) {
+if (serverArgs.h ?? serverArgs.help) {
   console.log(`Deno File Server
   Serves a local directory in HTTP.
 
@@ -125,8 +126,8 @@ async function serveDir(
   const listEntry: EntryInfo[] = [];
   const fileInfos = await readDir(dirPath);
   for (const fileInfo of fileInfos) {
-    const filePath = posix.join(dirPath, fileInfo.name);
-    const fileUrl = posix.join(dirUrl, fileInfo.name);
+    const filePath = posix.join(dirPath, fileInfo.name ?? "");
+    const fileUrl = posix.join(dirUrl, fileInfo.name ?? "");
     if (fileInfo.name === "index.html" && fileInfo.isFile()) {
       // in case index.html as dir...
       return await serveFile(req, filePath);
@@ -139,7 +140,7 @@ async function serveDir(
     listEntry.push({
       mode: modeToString(fileInfo.isDirectory(), mode),
       size: fileInfo.isFile() ? fileLenToString(fileInfo.len) : "",
-      name: fileInfo.name,
+      name: fileInfo.name ?? "",
       url: fileUrl
     });
   }
@@ -311,7 +312,7 @@ listenAndServe(
     }
     const fsPath = posix.join(target, normalizedUrl);
 
-    let response: Response;
+    let response: Response | undefined;
     try {
       const info = await stat(fsPath);
       if (info.isDirectory()) {
@@ -324,10 +325,11 @@ listenAndServe(
       response = await serveFallback(req, e);
     } finally {
       if (CORSEnabled) {
+        assert(response);
         setCORS(response);
       }
-      serverLog(req, response);
-      req.respond(response);
+      serverLog(req, response!);
+      req.respond(response!);
     }
   }
 );

http/file_server_test.ts

@@ -38,7 +38,7 @@ test(async function serveFile(): Promise<void> {
     assert(res.headers.has("access-control-allow-origin"));
     assert(res.headers.has("access-control-allow-headers"));
     assert(res.headers.has("content-type"));
-    assert(res.headers.get("content-type").includes("charset=utf-8"));
+    assert(res.headers.get("content-type")!.includes("charset=utf-8"));
     const downloadedFile = await res.text();
     const localFile = new TextDecoder().decode(
       await Deno.readFile("README.md")

http/server.ts

@@ -436,7 +436,7 @@ export class Server implements AsyncIterable<ServerRequest> {
   ): AsyncIterableIterator<ServerRequest> {
     const bufr = new BufReader(conn);
     const w = new BufWriter(conn);
-    let req: ServerRequest | Deno.EOF;
+    let req: ServerRequest | Deno.EOF | undefined;
     let err: Error | undefined;
 
     while (!this.closing) {

http/server_test.ts

@@ -545,7 +545,7 @@ test(async function testReadRequestError(): Promise<void> {
   for (const test of testCases) {
     const reader = new BufReader(new StringReader(test.in));
     let err;
-    let req: ServerRequest | Deno.EOF;
+    let req: ServerRequest | Deno.EOF | undefined;
     try {
       req = await readRequest(mockConn as Deno.Conn, reader);
     } catch (e) {
@@ -559,7 +559,7 @@ test(async function testReadRequestError(): Promise<void> {
       assert(err instanceof (test.err as typeof UnexpectedEOFError));
     } else {
       assert(req instanceof ServerRequest);
-      assert(test.headers != null);
+      assert(test.headers);
       assertEquals(err, undefined);
       assertNotEquals(req, Deno.EOF);
       for (const h of test.headers) {
@@ -719,6 +719,7 @@ if (Deno.build.os !== "win") {
       const serverRoutine = async (): Promise<void> => {
         let reqCount = 0;
         const server = serve(":8124");
+        // @ts-ignore
         const serverRid = server.listener["rid"];
         let connRid = -1;
         for await (const req of server) {

io/bufio.ts

@@ -311,7 +311,7 @@ export class BufReader implements Reader {
    */
   async readSlice(delim: number): Promise<Uint8Array | Deno.EOF> {
     let s = 0; // search start index
-    let slice: Uint8Array;
+    let slice: Uint8Array | undefined;
 
     while (true) {
       // Search buffer.

manual.md

@@ -1538,7 +1538,7 @@ Build with Cargo:
 cargo build -vv
 
 # Run:
-./target/debug/deno tests/002_hello.ts
+./target/debug/deno cli/tests/002_hello.ts
 ```
 
 #### Testing and Tools

node/events.ts

@@ -22,6 +22,7 @@
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 import { validateIntegerRange } from "./util.ts";
+import { assert } from "../testing/asserts.ts";
 
 export interface WrappedFunction extends Function {
   listener: Function;
@@ -163,7 +164,8 @@ export default class EventEmitter {
   private unwrapListeners(arr: Function[]): Function[] {
     const unwrappedListeners: Function[] = new Array(arr.length) as Function[];
     for (let i = 0; i < arr.length; i++) {
-      unwrappedListeners[i] = arr[i]["listener"] || arr[i];
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      unwrappedListeners[i] = (arr[i] as any)["listener"] || arr[i];
     }
     return unwrappedListeners;
   }
@@ -232,10 +234,12 @@ export default class EventEmitter {
     const wrapperContext = {
       eventName: eventName,
       listener: listener,
-      rawListener: wrapper,
+      rawListener: (wrapper as unknown) as WrappedFunction,
       context: this
     };
-    const wrapped = wrapper.bind(wrapperContext);
+    const wrapped = (wrapper.bind(
+      wrapperContext
+    ) as unknown) as WrappedFunction;
     wrapperContext.rawListener = wrapped;
     wrapped.listener = listener;
     return wrapped as WrappedFunction;
@@ -275,7 +279,7 @@ export default class EventEmitter {
       return this;
     }
 
-    if (this._events.has(eventName)) {
+    if (eventName && this._events.has(eventName)) {
       const listeners = (this._events.get(eventName) as Array<
         Function | WrappedFunction
       >).slice(); // Create a copy; We use it AFTER it's deleted.
@@ -299,14 +303,19 @@ export default class EventEmitter {
    */
   public removeListener(eventName: string | symbol, listener: Function): this {
     if (this._events.has(eventName)) {
-      const arr: Array<Function | WrappedFunction> = this._events.get(
-        eventName
-      );
+      const arr:
+        | Array<Function | WrappedFunction>
+        | undefined = this._events.get(eventName);
+
+      assert(arr);
 
       let listenerIndex = -1;
       for (let i = arr.length - 1; i >= 0; i--) {
         // arr[i]["listener"] is the reference to the listener inside a bound 'once' wrapper
-        if (arr[i] == listener || arr[i]["listener"] == listener) {
+        if (
+          arr[i] == listener ||
+          (arr[i] && (arr[i] as WrappedFunction)["listener"] == listener)
+        ) {
           listenerIndex = i;
           break;
         }
@@ -421,8 +430,10 @@ export function on(
 ): AsyncInterable {
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   const unconsumedEventValues: any[] = [];
-  const unconsumedPromises = [];
-  let error = null;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const unconsumedPromises: any[] = [];
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  let error: Error | null = null;
   let finished = false;
 
   const iterator = {
@@ -476,7 +487,7 @@ export function on(
     },
 
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    [Symbol.asyncIterator](): AsyncIterable<any> {
+    [Symbol.asyncIterator](): any {
       return this;
     }
   };

node/events_test.ts

@@ -17,7 +17,7 @@ test({
   fn() {
     let eventsFired: string[] = [];
     const testEmitter = new EventEmitter();
-    testEmitter.on("newListener", event => {
+    testEmitter.on("newListener", (event: string) => {
       if (event !== "newListener") {
         eventsFired.push("newListener");
       }
@@ -81,20 +81,23 @@ test({
   fn() {
     const testEmitter = new EventEmitter();
     const eventsFired: string[] = [];
-    testEmitter.on("event", oneArg => {
+    testEmitter.on("event", (oneArg: string) => {
       eventsFired.push("event(" + oneArg + ")");
     });
-    testEmitter.on("event", (oneArg, twoArg) => {
+    testEmitter.on("event", (oneArg: string, twoArg: string) => {
       eventsFired.push("event(" + oneArg + ", " + twoArg + ")");
     });
 
     testEmitter.on("non-event", shouldNeverBeEmitted);
 
-    testEmitter.on("event", (oneArg, twoArg, threeArg) => {
-      eventsFired.push(
-        "event(" + oneArg + ", " + twoArg + ", " + threeArg + ")"
-      );
-    });
+    testEmitter.on(
+      "event",
+      (oneArg: string, twoArg: string, threeArg: string) => {
+        eventsFired.push(
+          "event(" + oneArg + ", " + twoArg + ", " + threeArg + ")"
+        );
+      }
+    );
     testEmitter.emit("event", 1, 2, 3);
     assertEquals(eventsFired, ["event(1)", "event(1, 2)", "event(1, 2, 3)"]);
   }

node/global.ts

@@ -1 +1,2 @@
-window["global"] = window;
+// @ts-ignore
+globalThis["global"] = globalThis;

node/module.ts

@@ -40,7 +40,7 @@ const isWindows = path.isWindows;
 const relativeResolveCache = Object.create(null);
 
 let requireDepth = 0;
-let statCache = null;
+let statCache: Map<string, StatResult> | null = null;
 
 type StatResult = -1 | 0 | 1;
 // Returns 0 if the path refers to
@@ -64,7 +64,11 @@ function stat(filename: string): StatResult {
   }
 }
 
-function updateChildren(parent: Module, child: Module, scan: boolean): void {
+function updateChildren(
+  parent: Module | null,
+  child: Module,
+  scan: boolean
+): void {
   const children = parent && parent.children;
   if (children && !(scan && children.includes(child))) {
     children.push(child);
@@ -75,17 +79,17 @@ class Module {
   id: string;
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   exports: any;
-  parent?: Module;
-  filename: string;
+  parent: Module | null;
+  filename: string | null;
   loaded: boolean;
   children: Module[];
   paths: string[];
   path: string;
-  constructor(id = "", parent?: Module) {
+  constructor(id = "", parent?: Module | null) {
     this.id = id;
     this.exports = {};
-    this.parent = parent;
-    updateChildren(parent, this, false);
+    this.parent = parent || null;
+    updateChildren(parent || null, this, false);
     this.filename = null;
     this.loaded = false;
     this.children = [];
@@ -229,25 +233,25 @@ class Module {
             fakeParent.paths = Module._nodeModulePaths(path);
             const lookupPaths = Module._resolveLookupPaths(request, fakeParent);
 
-            for (let j = 0; j < lookupPaths.length; j++) {
-              if (!paths.includes(lookupPaths[j])) paths.push(lookupPaths[j]);
+            for (let j = 0; j < lookupPaths!.length; j++) {
+              if (!paths.includes(lookupPaths![j])) paths.push(lookupPaths![j]);
             }
           }
         }
       } else if (options.paths === undefined) {
-        paths = Module._resolveLookupPaths(request, parent);
+        paths = Module._resolveLookupPaths(request, parent)!;
       } else {
         throw new Error("options.paths is invalid");
       }
     } else {
-      paths = Module._resolveLookupPaths(request, parent);
+      paths = Module._resolveLookupPaths(request, parent)!;
     }
 
     // Look up the filename first, since that's the cache key.
     const filename = Module._findPath(request, paths, isMain);
     if (!filename) {
       const requireStack = [];
-      for (let cursor = parent; cursor; cursor = cursor.parent) {
+      for (let cursor: Module | null = parent; cursor; cursor = cursor.parent) {
         requireStack.push(cursor.filename || cursor.id);
       }
       let message = `Cannot find module '${request}'`;
@@ -341,7 +345,7 @@ class Module {
   //    object.
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   static _load(request: string, parent: Module, isMain: boolean): any {
-    let relResolveCacheIdentifier;
+    let relResolveCacheIdentifier: string | undefined;
     if (parent) {
       // Fast path for (lazy loaded) modules in the same directory. The indirect
       // caching is required to allow cache invalidation without changing the old
@@ -385,6 +389,7 @@ class Module {
 
     Module._cache[filename] = module;
     if (parent !== undefined) {
+      assert(relResolveCacheIdentifier);
       relativeResolveCache[relResolveCacheIdentifier] = filename;
     }
 
@@ -397,6 +402,7 @@ class Module {
       if (threw) {
         delete Module._cache[filename];
         if (parent !== undefined) {
+          assert(relResolveCacheIdentifier);
           delete relativeResolveCache[relResolveCacheIdentifier];
         }
       } else if (
@@ -602,7 +608,7 @@ for (const id of nativeModulePolyfill.keys()) {
   Module.builtinModules.push(id);
 }
 
-let modulePaths = [];
+let modulePaths: string[] = [];
 
 // Given a module name, and a list of paths to test, returns the first
 // matching file in the following precedence.
@@ -664,7 +670,7 @@ function readPackage(requestPath: string): PackageInfo | null {
 }
 
 function readPackageScope(
-  checkPath
+  checkPath: string
 ): { path: string; data: PackageInfo } | false {
   const rootSeparatorIndex = checkPath.indexOf(path.sep);
   let separatorIndex;
@@ -987,6 +993,7 @@ const CircularRequirePrototypeWarningProxy = new Proxy(
   {
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     get(target, prop): any {
+      // @ts-ignore
       if (prop in target) return target[prop];
       emitCircularRequireWarning(prop);
       return undefined;
@@ -1150,7 +1157,7 @@ function getPathFromURLWin32(url: URL): string {
   let pathname = url.pathname;
   for (let n = 0; n < pathname.length; n++) {
     if (pathname[n] === "%") {
-      const third = pathname.codePointAt(n + 2) | 0x20;
+      const third = pathname.codePointAt(n + 2)! | 0x20;
       if (
         (pathname[n + 1] === "2" && third === 102) || // 2f 2F /
         (pathname[n + 1] === "5" && third === 99)
@@ -1165,7 +1172,7 @@ function getPathFromURLWin32(url: URL): string {
   pathname = pathname.replace(forwardSlashRegEx, "\\");
   pathname = decodeURIComponent(pathname);
   // TODO: handle windows hostname case (needs bindings)
-  const letter = pathname.codePointAt(1) | 0x20;
+  const letter = pathname.codePointAt(1)! | 0x20;
   const sep = pathname[2];
   if (
     letter < CHAR_LOWERCASE_A ||
@@ -1184,7 +1191,7 @@ function getPathFromURLPosix(url: URL): string {
   const pathname = url.pathname;
   for (let n = 0; n < pathname.length; n++) {
     if (pathname[n] === "%") {
-      const third = pathname.codePointAt(n + 2) | 0x20;
+      const third = pathname.codePointAt(n + 2)! | 0x20;
       if (pathname[n + 1] === "2" && third === 102) {
         throw new Error(
           "Invalid file URL path: must not include encoded / characters"

node/os.ts

@@ -123,7 +123,7 @@ export function getPriority(pid = 0): number {
 }
 
 /** Returns the string path of the current user's home directory. */
-export function homedir(): string {
+export function homedir(): string | null {
   return Deno.dir("home");
 }
 
@@ -157,7 +157,7 @@ export function release(): string {
 
 /** Not yet implemented */
 export function setPriority(pid: number, priority?: number): void {
-  /* The node API has the 'pid' as the first parameter and as optional.  
+  /* The node API has the 'pid' as the first parameter and as optional.
        This makes for a problematic implementation in Typescript. */
   if (priority === undefined) {
     priority = pid;

path/utils.ts

@@ -46,13 +46,13 @@ export function normalizeString(
   let lastSegmentLength = 0;
   let lastSlash = -1;
   let dots = 0;
-  let code: number;
+  let code: number | undefined;
   for (let i = 0, len = path.length; i <= len; ++i) {
     if (i < len) code = path.charCodeAt(i);
-    else if (isPathSeparator(code)) break;
+    else if (isPathSeparator(code!)) break;
     else code = CHAR_FORWARD_SLASH;
 
-    if (isPathSeparator(code)) {
+    if (isPathSeparator(code!)) {
       if (lastSlash === i - 1 || dots === 1) {
         // NOOP
       } else if (lastSlash !== i - 1 && dots === 2) {

path/win32.ts

@@ -303,7 +303,7 @@ export function join(...paths: string[]): string {
   if (pathsCount === 0) return ".";
 
   let joined: string | undefined;
-  let firstPart: string;
+  let firstPart: string | null = null;
   for (let i = 0; i < pathsCount; ++i) {
     const path = paths[i];
     assertPath(path);

textproto/mod.ts

@@ -67,7 +67,7 @@ export class TextProtoReader {
    */
   async readMIMEHeader(): Promise<Headers | Deno.EOF> {
     const m = new Headers();
-    let line: Uint8Array;
+    let line: Uint8Array | undefined;
 
     // The first line cannot start with a leading space.
     let buf = await this.r.peek(1);
@@ -135,7 +135,7 @@ export class TextProtoReader {
 
   async readLineSlice(): Promise<Uint8Array | Deno.EOF> {
     // this.closeDot();
-    let line: Uint8Array;
+    let line: Uint8Array | undefined;
     while (true) {
       const r = await this.r.readLine();
       if (r === Deno.EOF) return Deno.EOF;

util/deep_assign.ts

@@ -1,4 +1,6 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+import { assert } from "../testing/asserts.ts";
+
 export function deepAssign(
   target: Record<string, unknown>,
   ...sources: object[]
@@ -24,6 +26,7 @@ export function deepAssign(
       if (typeof target[key] !== `object` || !target[key]) {
         target[key] = {};
       }
+      assert(value);
       deepAssign(target[key] as Record<string, unknown>, value);
     });
   }