fix(middleware-code-coverage): Lazy evaluate exclude patterns (#528)

This prevents the initial evaluation of exclude patterns on middleware
initialization, which is not necessary in case the middleware is not
used.

Calculating exclude patterns requires to read and parse all .library
files of the project and its dependencies.

Author: matz3

packages/middleware-code-coverage/lib/middleware.js

@@ -3,7 +3,9 @@ import {
 	createInstrumentationConfig,
 	shouldInstrumentResource,
 	getLatestSourceMap,
-	readJsonFile} from "./util.js";
+	readJsonFile,
+	getLibraryCoverageExcludePatterns
+} from "./util.js";
 import {createInstrumenter} from "istanbul-lib-instrument";
 import reportCoverage from "./coverage-reporter.js";
 import bodyParser from "body-parser";
@@ -33,10 +35,7 @@ import {promisify} from "node:util";
  * @returns {Function} Middleware function to use
  */
 export default async function({log, middlewareUtil, options={}, resources}) {
-	const config = await createInstrumentationConfig(
-		options.configuration,
-		resources.all
-	);
+	const config = await createInstrumentationConfig(options.configuration);
 	const {
 		report: reporterConfig,
 		instrument: instrumenterConfig,
@@ -104,9 +103,22 @@ export default async function({log, middlewareUtil, options={}, resources}) {
 		)
 	);
 
+	let excludePatterns;
+
 	router.use(async (req, res, next) => {
+		// Lazy initialize exclude patterns
+		if (excludePatterns === undefined) {
+			// Custom patterns take precedence over .library defined patterns (also when set to null)
+			if (generalConfig.excludePatterns !== undefined) {
+				excludePatterns = generalConfig.excludePatterns;
+			} else {
+				// Read patterns from .library files, this should only be done if needed and only once
+				excludePatterns = await getLibraryCoverageExcludePatterns(resources.all);
+			}
+		}
+
 		// Skip files which should not be instrumented
-		if (!shouldInstrumentResource(req, generalConfig)) {
+		if (!shouldInstrumentResource(req, excludePatterns)) {
 			next();
 			return;
 		}

packages/middleware-code-coverage/lib/util.js

@@ -7,18 +7,15 @@ import {readFile} from "node:fs/promises";
  *
  * @public
  * @param {object} configuration instrumentation configuration
- * @param {@ui5/fs/Resource[]} resources
  * @returns {Promise<object>} configuration
  */
-export async function createInstrumentationConfig(configuration = {}, resources) {
-	const excludedPatterns = resources ? await excludePatterns(resources) : [];
-
+export async function createInstrumentationConfig(configuration = {}) {
 	const {instrument, report, ...generalConfig} = configuration;
 
 	return {
 		// General configuration
 		cwd: "./",
-		excludePatterns: excludedPatterns,
+
 		// General config overwrites
 		...generalConfig,
 
@@ -55,17 +52,17 @@ export function getLatestSourceMap(instrumenter) {
  *
  * @public
  * @param {object} request
- * @param {object} config
+ * @param {Array<RegExp|string>} excludePatterns Patterns to exclude file from instrumentation (RegExp or string)
  * @returns {boolean}
  */
-export function shouldInstrumentResource(request, config) {
+export function shouldInstrumentResource(request, excludePatterns) {
 	return (
 		request.path &&
 		request.path.endsWith(".js") && // Only .js file requests
 		!isFalsyValue(request.query.instrument) && // instrument only flagged files, ignore "falsy" values
-		!(config && config.excludePatterns || []).some((pattern) => {
+		!(excludePatterns || []).some((pattern) => {
 			if (pattern instanceof RegExp) {
-				// The ones comming from .library files are regular expressions
+				// The ones coming from .library files are regular expressions
 				return pattern.test(request.path);
 			} else {
 				return request.path.includes(pattern);
@@ -131,13 +128,13 @@ function isFalsyValue(value) {
  * Note: We might consider to move this utility into the @ui5/project
  *
  * @private
- * @param {@ui5/fs/Resource[]} resources
+ * @param {@ui5/fs/AbstractReader} reader
  * @returns {Promise<RegExp[]>} exclude patterns
  */
-async function excludePatterns(resources) {
+export async function getLibraryCoverageExcludePatterns(reader) {
 	const aExcludes = [];
 	// Read excludes from .library files
-	const aDotLibrary = await resources.byGlob(["/resources/**/.library"]);
+	const aDotLibrary = await reader.byGlob(["/resources/**/.library"]);
 	for (const oDotLibrary of aDotLibrary) {
 		const content = await oDotLibrary.getString();
 		const result = await xml2js.parseStringPromise(content);