Add a couple additional lints to ensure consistent style

.eslintrc

@@ -1,6 +1,11 @@
 {
   "extends": "./node_modules/gts/",
   "rules": {
+    "@typescript-eslint/explicit-function-return-type": [
+      "error",
+      {"allowExpressions": true}
+    ],
+    "func-style": ["error", "declaration"],
     "prefer-const": ["error", {"destructuring": "all"}],
     // It would be nice to sort import declaration order as well, but that's not
     // autofixable and it's not worth the effort of handling manually.

lib/src/compiler.test.ts

@@ -9,7 +9,7 @@ import * as compilerModule from './compiler/utils';
 import {Compiler, initCompiler} from './compiler/sync';
 
 const createDispatcher = jest.spyOn(compilerModule, 'createDispatcher');
-function getIdHistory() {
+function getIdHistory(): number[] {
   return createDispatcher.mock.calls.map(([id]) => id);
 }
 

lib/src/exception.ts

@@ -19,7 +19,7 @@ export class Exception extends Error implements SassException {
     this.span = deprotofySourceSpan(failure.span!);
   }
 
-  toString() {
+  toString(): string {
     return this.message;
   }
 }

lib/src/legacy/value/wrap.ts

@@ -42,7 +42,7 @@ export function wrapFunction<sync extends 'sync' | 'async'>(
   } else {
     return args =>
       new Promise((resolve, reject) => {
-        const done = (result: unknown) => {
+        function done(result: unknown): void {
           try {
             if (result instanceof Error) {
               reject(result);
@@ -52,7 +52,7 @@ export function wrapFunction<sync extends 'sync' | 'async'>(
           } catch (error: unknown) {
             reject(error);
           }
-        };
+        }
 
         // The cast here is necesary to work around microsoft/TypeScript#33815.
         const syncResult = (callback as (...args: unknown[]) => unknown).apply(

lib/src/packet-transformer.test.ts

@@ -55,7 +55,7 @@ describe('packet transformer', () => {
   describe('decode', () => {
     let rawBuffers$: Subject<Buffer>;
 
-    function expectDecoding(expected: Buffer[], done: () => void) {
+    function expectDecoding(expected: Buffer[], done: () => void): void {
       const actual: Buffer[] = [];
       packets.outboundProtobufs$.subscribe({
         next: protobuf => actual.push(protobuf),

lib/src/request-tracker.ts

@@ -16,7 +16,7 @@ export class RequestTracker {
   > = [];
 
   /** The next available request ID. */
-  get nextId() {
+  get nextId(): number {
     for (let i = 0; i < this.requests.length; i++) {
       if (this.requests[i] === undefined || this.requests[i] === null) {
         return i;
@@ -32,7 +32,7 @@ export class RequestTracker {
   add(
     id: number,
     expectedResponseType: InboundResponseType | OutboundResponseType
-  ) {
+  ): void {
     if (id < 0) {
       throw Error(`Invalid request ID ${id}.`);
     } else if (this.requests[id]) {
@@ -47,7 +47,7 @@ export class RequestTracker {
    * Resolves a pending request with matching ID `id` and expected response type
    * `type`. Throws an error if the Protocol Error is violated.
    */
-  resolve(id: number, type: InboundResponseType | OutboundResponseType) {
+  resolve(id: number, type: InboundResponseType | OutboundResponseType): void {
     if (this.requests[id] === undefined || this.requests[id] === null) {
       throw Error(`Response ID ${id} does not match any pending requests.`);
     } else if (this.requests[id] !== type) {

lib/src/value/calculations.ts

@@ -23,9 +23,12 @@ function assertCalculationValue(value: CalculationValue): void {
   }
 }
 
-const isValidClampArg = (value: CalculationValue): boolean =>
-  value instanceof CalculationInterpolation ||
-  (value instanceof SassString && !value.hasQuotes);
+function isValidClampArg(value: CalculationValue): boolean {
+  return (
+    value instanceof CalculationInterpolation ||
+    (value instanceof SassString && !value.hasQuotes)
+  );
+}
 
 /* A SassScript calculation */
 export class SassCalculation extends Value {

lib/src/value/color.ts

@@ -350,7 +350,7 @@ function hwbToRgb(
   hue: number,
   scaledWhiteness: number,
   scaledBlackness: number
-) {
+): number {
   const factor = 1 - scaledWhiteness - scaledBlackness;
   const channel = hueToRgb(0, 1, hue) * factor + scaledWhiteness;
   return fuzzyRound(channel * 255);

lib/src/value/utils.ts

@@ -116,7 +116,7 @@ export function fuzzyAssertInRange(
 }
 
 /** Returns `dividend % modulus`, but always in the range `[0, modulus)`. */
-export function positiveMod(dividend: number, modulus: number) {
+export function positiveMod(dividend: number, modulus: number): number {
   const result = dividend % modulus;
   return result < 0 ? result + modulus : result;
 }

test/utils.ts

@@ -48,7 +48,7 @@ export function expectEqualIgnoringWhitespace(
   string1: string,
   string2: string
 ): void {
-  function strip(str: string) {
+  function strip(str: string): string {
     return str.replace(/\s+/g, '');
   }
   expect(strip(string1)).toBe(strip(string2));

tool/get-deprecations.ts

@@ -34,7 +34,7 @@ function toVersionCode(version: string | undefined): string {
  * Generates the list of deprecations based on the YAML file in the language
  * repo.
  */
-export async function getDeprecations(outDirectory: string) {
+export async function getDeprecations(outDirectory: string): Promise<void> {
   const yamlText = fs.readFileSync(yamlFile, 'utf8');
 
   const deprecations = parse(yamlText) as YamlData;

tool/prepare-release.ts

@@ -35,7 +35,7 @@ void (async () => {
 
 // Quick sanity checks to make sure the release we are preparing is a suitable
 // candidate for release.
-async function sanityCheckBeforeRelease() {
+async function sanityCheckBeforeRelease(): Promise<void> {
   console.log('Running sanity checks before releasing.');
   const releaseVersion = pkg.version;