use toolchain to get javap executable path for tests

build.gradle.kts

@@ -85,6 +85,14 @@ val filtered = tasks.register<FilterTestClasspath>("filteredTestClasspath") {
     new.from(testDataNewTargets.output)
 }
 
+val javapPath = javaToolchains.launcherFor {
+    languageVersion.set(JavaLanguageVersion.of(17))
+}.map { it.metadata.installationPath.asFile.toPath().resolve("bin/javap") }
+
+tasks.withType<Test> {
+    environment("JAVAP_PATH", javapPath.get())
+}
+
 dependencies {
     testImplementation(files(filtered.flatMap { it.outputDir }))
     testImplementation(testDataNewTargets.output)

src/test/java/io/papermc/asm/TestUtil.java

@@ -15,6 +15,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Function;
 import org.checkerframework.checker.nullness.qual.NonNull;
@@ -33,6 +34,7 @@
 public final class TestUtil {
     private TestUtil() {
     }
+    private static final String JAVAP_PATH = Objects.requireNonNullElse(System.getenv("JAVAP_PATH"), "javap");// fallback to hoping its on actual PATH
 
     public static RewriteRuleVisitorFactory testingVisitorFactory(final RewriteRule rewriteRule) {
         return RewriteRuleVisitorFactory.create(Opcodes.ASM9, rewriteRule, ClassInfoProvider.basic());
@@ -132,9 +134,9 @@ private static <T extends Throwable> void assertProcessedMatchesExpected_(
                 return;
             } else {
                 // Try to get a javap diff
-                // final boolean proceed = checkJavapDiff(name, expected.get(name), processed.get(name), Arrays.asList("javap", "-c", "-p"));
+                // final boolean proceed = checkJavapDiff(name, expected.get(name), processed.get(name), Arrays.asList(JAVAP_PATH, "-c", "-p"));
                 // verbose is too useful for invokedynamic debugging to omit
-                checkJavapDiff(name, expected.get(name), processed.get(name), Arrays.asList("javap", "-c", "-p", "-v"));
+                checkJavapDiff(name, expected.get(name), processed.get(name), Arrays.asList(JAVAP_PATH, "-c", "-p", "-v"));
 
                 // If javap failed, just assert the bytes equal
                 assertArrayEquals(