Use existing modules if package locks match

bin/plugin/commands/performance.js

@@ -17,6 +17,7 @@ const {
 	runShellScript,
 	readJSONFile,
 	writeJSONFile,
+	getFileHash,
 } = require( '../lib/utils' );
 const config = require( '../config' );
 
@@ -423,8 +424,35 @@ async function runPerformanceTests( refs, options ) {
 						.reset( 'hard', `origin/${ ref }` )
 						.checkout( ref );
 
-					logRefAction( 'Installing dependencies' );
-					await runShellScript( 'npm ci', buildDir );
+					// Compare package-lock.json files to see if we can use the
+					// node modules already installed within the root directory.
+					const rootPackageLockHash = getFileHash(
+						path.join( CWD, 'package-lock.json' )
+					);
+					const targetPackageLockHash = getFileHash(
+						path.join( buildDir, 'package-lock.json' )
+					);
+
+					if ( rootPackageLockHash === targetPackageLockHash ) {
+						logRefAction( 'Using existing dependencies' );
+
+						const sourceNodeModulesPath = path.join(
+							CWD,
+							'node_modules'
+						);
+						const targetNodeModulesPath = path.join(
+							buildDir,
+							'node_modules'
+						);
+
+						await runShellScript(
+							`ln -s ${ sourceNodeModulesPath } ${ targetNodeModulesPath }`
+						);
+					} else {
+						logRefAction( 'Installing dependencies' );
+						await runShellScript( 'npm ci', buildDir );
+					}
+
 					doBuild = true;
 				}
 			}

bin/plugin/lib/utils.js

@@ -8,6 +8,7 @@ const childProcess = require( 'child_process' );
 const { v4: uuid } = require( 'uuid' );
 const path = require( 'path' );
 const os = require( 'os' );
+const crypto = require( 'crypto' );
 
 /**
  * Internal dependencies
@@ -134,11 +135,25 @@ function getRandomTemporaryPath() {
 	return path.join( os.tmpdir(), uuid() );
 }
 
+/**
+ * Function to get the SHA256 hash of a file.
+ *
+ * @param {string} filePath Path to the file to be hashed.
+ * @return {string} SHA of the given file.
+ */
+function getFileHash( filePath ) {
+	const fileContent = fs.readFileSync( filePath );
+	const hash = crypto.createHash( 'sha256' );
+	hash.update( fileContent );
+	return hash.digest( 'hex' );
+}
+
 module.exports = {
 	askForConfirmation,
 	runStep,
 	readJSONFile,
 	writeJSONFile,
 	runShellScript,
 	getRandomTemporaryPath,
+	getFileHash,
 };