Performance: Add comment with perf changes in PRs

.github/workflows/performance.yml

@@ -91,6 +91,10 @@ jobs:
                   name: performance-results
                   path: ${{ env.WP_ARTIFACTS_PATH }}/*.performance-results*.json
 
+            - name: Check performance regression
+              if: github.event_name == 'pull_request'
+              run: node ./bin/check-performance-regression.js
+
             - name: Publish performance results
               if: github.event_name == 'push'
               env:

bin/check-performance-regression.js

@@ -0,0 +1,76 @@
+#!/usr/bin/env node
+
+/**
+ * External dependencies
+ */
+const fs = require( 'fs' );
+const path = require( 'path' );
+
+const resultsPath = process.env.WP_ARTIFACTS_PATH;
+const maxRegressionFactor = 1.3; // fail on >30% regression
+const regressedMetrics = [];
+
+fs.readdir( resultsPath, ( err, files ) => {
+	if ( err ) {
+		console.error( 'Error reading directory:', err );
+		process.exit( 1 );
+	}
+	const curatedResults = files.filter(
+		( file ) =>
+			file.endsWith( '.performance-results.json' ) &&
+			! file.includes( '_round-' )
+	);
+
+	if ( curatedResults.length === 0 ) {
+		console.error( 'No performance results found.' );
+		process.exit( 1 );
+	}
+
+	curatedResults.forEach( ( file ) => {
+		const data = JSON.parse(
+			fs.readFileSync( path.join( resultsPath, file ), 'utf8' )
+		);
+
+		const trunkMetrics = data.trunk;
+		const branchMetrics =
+			data[ Object.keys( data ).find( ( key ) => key !== 'trunk' ) ];
+
+		if ( ! trunkMetrics || ! branchMetrics ) {
+			console.error( `No trunk or branch metrics found.` );
+			process.exit( 1 );
+		}
+
+		Object.keys( trunkMetrics ).forEach( ( metric ) => {
+			const trunkValue = trunkMetrics[ metric ];
+			const branchValue = branchMetrics[ metric ];
+
+			if ( branchValue > trunkValue * maxRegressionFactor ) {
+				regressedMetrics.push( {
+					file,
+					metric,
+					branchValue,
+					trunkValue,
+				} );
+			}
+		} );
+	} );
+
+	if ( regressedMetrics.length > 0 ) {
+		console.log( 'Performance regression detected:' );
+		regressedMetrics.forEach(
+			( { file, metric, branchValue, trunkValue } ) => {
+				const percent = (
+					( ( branchValue - trunkValue ) / trunkValue ) *
+					100
+				).toFixed( 2 );
+
+				console.log(
+					`- In ${ file }: ${ metric } increased by ${ percent }% (from ${ trunkValue } to ${ branchValue })`
+				);
+			}
+		);
+		process.exit( 1 );
+	} else {
+		console.log( 'No significant performance regression detected.' );
+	}
+} );