LinkageError when building Spock

I opened Spock and let it build.

I get for spock-specs/src/test/groovy/org/spockframework/smoke/WithBlocks.groovy this Problem reported:

Groovy:General error during instruction selection: java.lang.LinkageError: loader constraint violation: loader java.net.URLClassLoader @60e6b90d wants to load abstract class groovyjarjarasm.asm.MethodVisitor. A different abstract class with the same name was previously loaded by org.eclipse.osgi.internal.loader.EquinoxClassLoader @5c02234. (groovyjarjarasm.asm.MethodVisitor is in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @5c02234, parent loader 'platform')

I don't see anything in the Eclipse log.

I put a breakpoint for the LinkageError and got this stacktrace:

at java.lang.LinkageError.<init>(LinkageError.java:55)
at java.lang.ClassLoader.defineClass1(ClassLoader.java:-1)
at java.lang.ClassLoader.defineClass(ClassLoader.java:962)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:144)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:454)
at java.net.URLClassLoader.findClass(URLClassLoader.java:367)
at java.lang.ClassLoader.loadClass(ClassLoader.java:557)
at java.lang.ClassLoader.loadClass(ClassLoader.java:490)
at org.spockframework.compiler.CurrentClosureExpression.visit(CurrentClosureExpression.java:52)
at org.codehaus.groovy.classgen.AsmClassGenerator.visitBytecodeExpression(AsmClassGenerator.java:1903)
at org.codehaus.groovy.classgen.BytecodeExpression.visit(BytecodeExpression.java:55)
at org.codehaus.groovy.classgen.asm.InvocationWriter.loadArguments(InvocationWriter.java:265)
at org.codehaus.groovy.classgen.asm.InvocationWriter.writeDirectMethodCall(InvocationWriter.java:215)
at org.codehaus.groovy.classgen.asm.InvocationWriter.makeDirectCall(InvocationWriter.java:313)
at org.codehaus.groovy.classgen.asm.InvocationWriter.makeCall(InvocationWriter.java:132)
at org.codehaus.groovy.classgen.asm.InvocationWriter.makeCall(InvocationWriter.java:126)
at org.codehaus.groovy.classgen.asm.InvocationWriter.writeInvokeMethod(InvocationWriter.java:456)
at org.codehaus.groovy.classgen.AsmClassGenerator.visitMethodCallExpression(AsmClassGenerator.java:1007)
at org.codehaus.groovy.ast.expr.MethodCallExpression.visit(MethodCallExpression.java:79)
at org.codehaus.groovy.classgen.asm.StatementWriter.writeReturn(StatementWriter.java:594)
at org.codehaus.groovy.classgen.AsmClassGenerator.visitReturnStatement(AsmClassGenerator.java:841)
at org.codehaus.groovy.ast.stmt.ReturnStatement.visit(ReturnStatement.java:73)
at org.codehaus.groovy.classgen.asm.StatementWriter.writeTryCatchFinally(StatementWriter.java:337)
at org.codehaus.groovy.classgen.AsmClassGenerator.visitTryCatchFinally(AsmClassGenerator.java:801)
at org.codehaus.groovy.ast.stmt.TryCatchStatement.visit(TryCatchStatement.java:48)
at org.codehaus.groovy.classgen.asm.StatementWriter.writeBlockStatement(StatementWriter.java:95)
at org.codehaus.groovy.classgen.AsmClassGenerator.visitBlockStatement(AsmClassGenerator.java:771)
at org.codehaus.groovy.ast.stmt.BlockStatement.visit(BlockStatement.java:72)
at org.codehaus.groovy.classgen.AsmClassGenerator.visitStdMethod(AsmClassGenerator.java:630)
at org.codehaus.groovy.classgen.AsmClassGenerator.visitConstructorOrMethod(AsmClassGenerator.java:565)
at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitMethod(ClassCodeVisitorSupport.java:125)
at org.codehaus.groovy.classgen.AsmClassGenerator.visitMethod(AsmClassGenerator.java:714)
at org.codehaus.groovy.ast.ClassNode.visitMethods(ClassNode.java:1242)
at org.codehaus.groovy.ast.ClassNode.visitContents(ClassNode.java:1235)
at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitClass(ClassCodeVisitorSupport.java:56)
at org.codehaus.groovy.classgen.AsmClassGenerator.visitClass(AsmClassGenerator.java:367)
at org.codehaus.groovy.control.CompilationUnit$2.call(CompilationUnit.java:829)
at org.codehaus.groovy.control.CompilationUnit$2.call(CompilationUnit.java:851)
at org.codehaus.groovy.control.CompilationUnit$IPrimaryClassNodeOperation.doPhaseOperation(CompilationUnit.java:980)
at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:678)
at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:652)
at org.codehaus.jdt.groovy.internal.compiler.ast.GroovyCompilationUnitDeclaration.processToPhase(GroovyCompilationUnitDeclaration.java:243)
at org.codehaus.jdt.groovy.internal.compiler.ast.GroovyCompilationUnitDeclaration.generateCode(GroovyCompilationUnitDeclaration.java:346)
at org.eclipse.jdt.internal.compiler.Compiler.process(Compiler.java:844)
at org.eclipse.jdt.internal.compiler.ProcessTaskManager.processing(ProcessTaskManager.java:135)
at org.eclipse.jdt.internal.compiler.ProcessTaskManager$$Lambda/0x000000001a11ad08.run(Unknown Source:-1)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:545)
at java.util.concurrent.FutureTask.run(FutureTask.java:328)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614)
at java.lang.Thread.runWith(Thread.java:1487)
at java.lang.Thread.run(Thread.java:1474)

Start by reproducing the build failure for spock-specs/src/test/groovy/org/spockframework/smoke/WithBlocks.groovy and inspect the reported stack trace, especially CurrentClosureExpression.visit. Investigate the conflicting groovyjarjarasm.asm.MethodVisitor class loaders. Done means the Spock build completes without the LinkageError.