chore: enforce return types

.eslintrc.json

@@ -1,3 +1,20 @@
 {
-  "extends": "./node_modules/gts"
+  "extends": "./node_modules/gts",
+  "overrides": [
+    {
+      "files": [
+        "dev/src/*.ts"
+      ],
+      "parser": "@typescript-eslint/parser",
+      "rules": {
+        "@typescript-eslint/explicit-function-return-type": [
+          "error",
+          {
+            "allowExpressions": true,
+            "allowTypedFunctionExpressions": true
+          }
+        ]
+      }
+    }
+  ]
 }

dev/src/backoff.ts

@@ -265,7 +265,7 @@ export class ExponentialBackoff {
    * @returns {number} The jitter to apply based on the current delay.
    * @private
    */
-  private jitterDelayMs() {
+  private jitterDelayMs(): number {
     return (Math.random() - 0.5) * this.jitterFactor * this.currentBaseMs;
   }
 }

dev/src/document-change.ts

@@ -73,7 +73,7 @@ export class DocumentChange<T = DocumentData> {
    * // Remove this listener.
    * unsubscribe();
    */
-  get type() {
+  get type(): DocumentChangeType {
     return this._type;
   }
 
@@ -96,7 +96,7 @@ export class DocumentChange<T = DocumentData> {
    * // Remove this listener.
    * unsubscribe();
    */
-  get doc() {
+  get doc(): QueryDocumentSnapshot<T> {
     return this._document;
   }
 
@@ -127,7 +127,7 @@ export class DocumentChange<T = DocumentData> {
    * // Remove this listener.
    * unsubscribe();
    */
-  get oldIndex() {
+  get oldIndex(): number {
     return this._oldIndex;
   }
 
@@ -159,7 +159,7 @@ export class DocumentChange<T = DocumentData> {
    * // Remove this listener.
    * unsubscribe();
    */
-  get newIndex() {
+  get newIndex(): number {
     return this._newIndex;
   }
 

dev/src/document.ts

@@ -695,7 +695,7 @@ export class DocumentMask {
    * @private
    * @return {boolean} Whether this document mask is empty.
    */
-  get isEmpty() {
+  get isEmpty(): boolean {
     return this._sortedPaths.length === 0;
   }
 
@@ -771,13 +771,13 @@ export class DocumentMask {
      * Applies this DocumentMask to 'data' and computes the list of field paths
      * that were specified in the mask but are not present in 'data'.
      */
-    const applyDocumentMask = (data: DocumentData) => {
+    const applyDocumentMask: (data: DocumentData) => DocumentData = data => {
       const remainingPaths = this._sortedPaths.slice(0);
 
-      const processObject = (
+      const processObject: (
         currentData: DocumentData,
         currentPath?: FieldPath
-      ) => {
+      ) => DocumentData | null = (currentData, currentPath) => {
         let result: DocumentData | null = null;
 
         Object.keys(currentData).forEach(key => {
@@ -902,7 +902,11 @@ export class DocumentTransform<T = DocumentData> {
   ): DocumentTransform<T> {
     const transforms = new Map<FieldPath, FieldTransform>();
 
-    function encode_(val: unknown, path: FieldPath, allowTransforms: boolean) {
+    function encode_(
+      val: unknown,
+      path: FieldPath,
+      allowTransforms: boolean
+    ): void {
       if (val instanceof FieldTransform && val.includeInDocumentTransform) {
         if (allowTransforms) {
           transforms.set(path, val);

dev/src/index.ts

@@ -1266,15 +1266,15 @@ export class Firestore {
     let streamInitialized = false;
 
     return new Promise<Duplex>((resolve, reject) => {
-      function streamReady() {
+      function streamReady(): void {
         if (!streamInitialized) {
           streamInitialized = true;
           logger('Firestore._initializeStream', requestTag, 'Releasing stream');
           resolve(resultStream);
         }
       }
 
-      function streamEnded() {
+      function streamEnded(): void {
         logger(
           'Firestore._initializeStream',
           requestTag,
@@ -1285,7 +1285,7 @@ export class Firestore {
         lifetime.resolve();
       }
 
-      function streamFailed(err: Error) {
+      function streamFailed(err: Error): void {
         if (!streamInitialized) {
           // If we receive an error before we were able to receive any data,
           // reject this stream.

dev/src/path.ts

@@ -245,7 +245,7 @@ export class ResourcePath extends Path<ResourcePath> {
    * database.
    * @private
    */
-  get relativeName() {
+  get relativeName(): string {
     return this.segments.join('/');
   }
 
@@ -543,7 +543,7 @@ export class FieldPath extends Path<FieldPath> {
    *
    * @returns {FieldPath}
    */
-  static documentId() {
+  static documentId(): FieldPath {
     return FieldPath._DOCUMENT_ID;
   }
 
@@ -556,7 +556,7 @@ export class FieldPath extends Path<FieldPath> {
    * @param {string|FieldPath} fieldPath The FieldPath to create.
    * @returns {FieldPath} A field path representation.
    */
-  static fromArgument(fieldPath: string | FieldPath) {
+  static fromArgument(fieldPath: string | FieldPath): FieldPath {
     // validateFieldPath() is used in all public API entry points to validate
     // that fromArgument() is only called with a Field Path or a string.
     return fieldPath instanceof FieldPath
@@ -613,7 +613,7 @@ export class FieldPath extends Path<FieldPath> {
    * @param segments Sequence of field names.
    * @returns The newly created FieldPath.
    */
-  construct(segments: string[]) {
+  construct(segments: string[]): FieldPath {
     return new FieldPath(...segments);
   }
 

dev/src/reference.ts

@@ -1054,7 +1054,7 @@ export class QueryOptions<T> {
     return this.fieldOrders.length > 0;
   }
 
-  isEqual(other: QueryOptions<T>) {
+  isEqual(other: QueryOptions<T>): boolean {
     if (this === other) {
       return true;
     }
@@ -1129,7 +1129,7 @@ export class Query<T = DocumentData> {
   static _extractFieldValues(
     documentSnapshot: DocumentSnapshot,
     fieldOrders: FieldOrder[]
-  ) {
+  ): unknown[] {
     const fieldValues: unknown[] = [];
 
     for (const fieldOrder of fieldOrders) {
@@ -2215,7 +2215,7 @@ export class CollectionReference<T = DocumentData> extends Query<T> {
    * Returns a resource path for this collection.
    * @private
    */
-  private get resourcePath() {
+  private get resourcePath(): ResourcePath {
     return this._queryOptions.parentPath.append(
       this._queryOptions.collectionId
     );

dev/src/timestamp.ts

@@ -69,7 +69,7 @@ export class Timestamp {
    *
    * @return {Timestamp} A new `Timestamp` representing the current date.
    */
-  static now() {
+  static now(): Timestamp {
     return Timestamp.fromMillis(Date.now());
   }
 
@@ -86,7 +86,7 @@ export class Timestamp {
    * @return {Timestamp} A new `Timestamp` representing the same point in time
    * as the given date.
    */
-  static fromDate(date: Date) {
+  static fromDate(date: Date): Timestamp {
     return Timestamp.fromMillis(date.getTime());
   }
 
@@ -103,7 +103,7 @@ export class Timestamp {
    * @return {Timestamp}  A new `Timestamp` representing the same point in time
    * as the given number of milliseconds.
    */
-  static fromMillis(milliseconds: number) {
+  static fromMillis(milliseconds: number): Timestamp {
     const seconds = Math.floor(milliseconds / 1000);
     const nanos = (milliseconds - seconds * 1000) * MS_TO_NANOS;
     return new Timestamp(seconds, nanos);
@@ -115,7 +115,7 @@ export class Timestamp {
    * @private
    * @param {Object} timestamp The `Timestamp` Protobuf object.
    */
-  static fromProto(timestamp: google.protobuf.ITimestamp) {
+  static fromProto(timestamp: google.protobuf.ITimestamp): Timestamp {
     return new Timestamp(Number(timestamp.seconds || 0), timestamp.nanos || 0);
   }
 

dev/src/transaction.ts

@@ -474,7 +474,7 @@ export class Transaction {
    * @private
    * @return A Promise that resolves after the delay expired.
    */
-  private async maybeBackoff(error?: GoogleError) {
+  private async maybeBackoff(error?: GoogleError): Promise<void> {
     if (error && error.code === Status.RESOURCE_EXHAUSTED) {
       this._backoff.resetToMax();
     }

dev/src/validate.ts

@@ -288,7 +288,7 @@ export function validateInteger(
 export function invalidArgumentMessage(
   arg: string | number,
   expectedType: string
-) {
+): string {
   return `${formatArgumentName(arg)} is not a valid ${expectedType}.`;
 }
 

dev/src/watch.ts

@@ -63,15 +63,15 @@ const ChangeType: {[k: string]: DocumentChangeType} = {
  * The comparator used for document watches (which should always get called with
  * the same document).
  */
-const DOCUMENT_WATCH_COMPARATOR = <T>(
+const DOCUMENT_WATCH_COMPARATOR: <T>(
   doc1: QueryDocumentSnapshot<T>,
   doc2: QueryDocumentSnapshot<T>
-) => {
+) => number = (doc1, doc2) => {
   assert(doc1 === doc2, 'Document watches only support one document.');
   return 0;
 };
 
-const EMPTY_FUNCTION = () => {};
+const EMPTY_FUNCTION: () => void = () => {};
 
 /**
  * @private
@@ -250,7 +250,7 @@ abstract class Watch<T = DocumentData> {
 
     this.initStream();
 
-    const unsubscribe = () => {
+    const unsubscribe: () => void = () => {
       logger('Watch.onSnapshot', this.requestTag, 'Unsubscribe called');
       // Prevent further callbacks.
       if (this.isActive) {

dev/src/write-batch.ts

@@ -121,6 +121,8 @@ interface WriteOp {
   precondition?: api.IPrecondition | null;
 }
 
+export type PendingWriteOp = () => WriteOp;
+
 /**
  * A Firestore WriteBatch that can be used to atomically commit multiple write
  * operations at once.
@@ -136,7 +138,7 @@ export class WriteBatch {
    * resulting `api.IWrite` will be sent to the backend.
    * @private
    */
-  private readonly _ops: Array<() => WriteOp> = [];
+  private readonly _ops: Array<PendingWriteOp> = [];
 
   private _committed = false;
 
@@ -202,7 +204,7 @@ export class WriteBatch {
 
     const precondition = new Precondition({exists: false});
 
-    const op = () => {
+    const op: PendingWriteOp = () => {
       const document = DocumentSnapshot.fromObject(documentRef, firestoreData);
       const write = document.toProto();
       if (!transform.isEmpty) {
@@ -254,7 +256,7 @@ export class WriteBatch {
 
     const conditions = new Precondition(precondition);
 
-    const op = () => {
+    const op: PendingWriteOp = () => {
       return {
         write: {
           delete: documentRef.formattedName,
@@ -326,7 +328,7 @@ export class WriteBatch {
     const transform = DocumentTransform.fromObject(documentRef, firestoreData);
     transform.validate();
 
-    const op = () => {
+    const op: PendingWriteOp = () => {
       const document = DocumentSnapshot.fromObject(documentRef, firestoreData);
 
       if (mergePaths) {
@@ -490,7 +492,7 @@ export class WriteBatch {
 
     const documentMask = DocumentMask.fromUpdateMap(updateMap);
 
-    const op = () => {
+    const op: PendingWriteOp = () => {
       const document = DocumentSnapshot.fromUpdateMap(documentRef, updateMap);
       const write = document.toProto();
       write!.updateMask = documentMask.toProto();
@@ -666,7 +668,7 @@ export class WriteBatch {
    * Resets the WriteBatch and dequeues all pending operations.
    * @private
    */
-  _reset() {
+  _reset(): void {
     this._ops.splice(0);
     this._committed = false;
   }