Print stats about run.javac comparison at the end of TestAll

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/AbstractModuleCompilationTest.java

@@ -163,6 +163,7 @@ protected Set<String> runConformModuleTest(String[] testFiles, String commandLin
 							System.err.println("Skip testing javac in "+testName());
 							continue;
 						}
+						numRunJavacTests++;
 						StringBuilder log = new StringBuilder();
 						try {
 							long compileResult = javacCompiler.compile(
@@ -250,6 +251,7 @@ void runNegativeModuleTest(String[] testFiles, String commandLine, String expect
 				if (javacCompiler.compliance < ClassFileConstants.JDK9)
 					continue;
 				JavacTestOptions.Excuse excuse = options.excuseFor(javacCompiler);
+				numRunJavacTests++;
 
 				String javacCommandLine = " -d " + javacOutput + ' ' + adjustForJavac(commandLine, null);
 				StringBuilder log = new StringBuilder();

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/AbstractRegressionTest.java

@@ -24,6 +24,8 @@
 package org.eclipse.jdt.core.tests.compiler.regression;
 
 import java.io.*;
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
 import java.net.URL;
 import java.nio.charset.Charset;
 import java.nio.file.Files;
@@ -92,6 +94,11 @@ public abstract class AbstractRegressionTest extends AbstractCompilerTest implem
 	protected static long PREVIEW_FEATURE_CLASS_FILE_CONST = ClassFileConstants.JDK25;
 	protected static int PREVIEW_FEATURE_LEVEL = 25;
 
+	// statistics for run.javac mode:
+	static int numRunJavacTests = 0;
+	static Set<JavacTestOptions.Excuse> javacBugs = new HashSet<>();
+	static Set<JavacTestOptions.Excuse> ecjBugs = new HashSet<>();
+
 	protected class Runner {
 		boolean shouldFlushOutputDirectory = true;
 		// input:
@@ -2781,6 +2788,7 @@ protected void runJavac(
 				e.printStackTrace();
 				mismatch = JavacTestOptions.MismatchType.JavaNotLaunched;
 			}
+			numRunJavacTests++;
 			handleMismatch(compiler, testName, testFiles, expectedCompilerLog, expectedOutputString,
 					expectedErrorString, compilerLog, output, err, excuse, mismatch);
 		}
@@ -2830,6 +2838,7 @@ void handleMismatch(JavacCompiler compiler, String testName, String[] testFiles,
 		JavacTestOptions.Excuse excuse, int mismatch) {
 	if (mismatch != 0) {
 		if (excuse != null && excuse.clears(mismatch)) {
+			recordBugHit(excuse);
 			excuse = null;
 		} else {
 			System.err.println("----------------------------------------");
@@ -4306,4 +4315,43 @@ protected Map<String, String> setPresetPreviewOptions() {
 		options.put(CompilerOptions.OPTION_ReportPreviewFeatures, CompilerOptions.IGNORE);
 		return options;
 	}
+
+	private static void recordBugHit(JavacTestOptions.Excuse excuse) {
+		if (excuse instanceof JavacTestOptions.JavacHasABug)
+			javacBugs.add(excuse);
+		else if (excuse instanceof JavacTestOptions.EclipseHasABug)
+			ecjBugs.add(excuse);
+	}
+
+	public static void printRunJavacStats() {
+		if (RUN_JAVAC || RUN_JAVAC_OPT_IN) {
+			System.out.println("Num tests with run.javac enabled: "+numRunJavacTests);
+			System.out.println("Num tests triggering a javac bug: "+javacBugs.size());
+			printBugConstants(javacBugs, JavacTestOptions.JavacHasABug.class);
+			System.out.println("Num tests triggering an ecj bug : "+ecjBugs.size());
+			printBugConstants(ecjBugs, JavacTestOptions.EclipseHasABug.class);
+		}
+	}
+
+	private static void printBugConstants(Set<JavacTestOptions.Excuse> bugs, Class<? extends JavacTestOptions.Excuse> clazz) {
+		List<String> bugNames = new ArrayList<>();
+		bugs: for (JavacTestOptions.Excuse bug : bugs) {
+			for (Class<?> aClazz : new Class<?>[] { clazz, JavacTestOptions.Excuse.class }) {
+				for (Field field : aClazz.getDeclaredFields()) {
+					if ((field.getModifiers() & Modifier.STATIC) != 0) {
+						try {
+							if (bug == field.get(null)) {
+								bugNames.add(field.getName());
+								continue bugs;
+							}
+						} catch (IllegalArgumentException | IllegalAccessException e) {
+							// ignore
+						}
+					}
+				}
+			}
+			bugNames.add("\tunknown excuse "+bug);
+		}
+		bugNames.stream().sorted().forEach(s -> System.out.println("\t"+s));
+	}
 }

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/JavadocTestForModule.java

@@ -236,6 +236,7 @@ void runNegativeModuleTest(String[] testFiles, String commandLine,
 				if (javacCompiler.compliance < ClassFileConstants.JDK9)
 					continue;
 				JavacTestOptions.Excuse excuse = options.excuseFor(javacCompiler);
+				numRunJavacTests++;
 
 				commandLine = adjustForJavac(commandLine, null);
 				StringBuilder log = new StringBuilder();

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/PrintRunJavacStats.java

@@ -0,0 +1,32 @@
+/*******************************************************************************
+ * Copyright (c) 2026 GK Software and others.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Stephan Herrmann - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.jdt.core.tests.compiler.regression;
+
+import junit.framework.Test;
+
+/**
+ * This test class exists for the sole purpose of printing statistics about tests run as comparison of ecj vs javac.
+ * It is be integrated in {@link TestAll} as the very last test in the suite.
+ */
+public class PrintRunJavacStats extends AbstractRegressionTest {
+	public PrintRunJavacStats(String name) {
+		super(name);
+	}
+	public static Test suite() {
+		return buildMinimalComplianceTestSuite(PrintRunJavacStats.class, FIRST_SUPPORTED_JAVA_VERSION);
+	}
+	public void testPrint() {
+		printRunJavacStats();
+	}
+}

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/TestAll.java

@@ -294,6 +294,7 @@ public static Test suite() {
 	}
 
 	all.addTest(new TestSuite(Jsr14Test.class));
+	all.addTest(new TestSuite(PrintRunJavacStats.class)); // the very last test to capture statistics of all tests
 	return all;
 }
 }