8340840: jshell ClassFormatError when making inner class static #27665

lahodaj · 2025-10-07T07:15:50Z

Consider a JShell interaction like:

jshell> class O { class I {} }
|  created class O

jshell> var i = new O().new I();
i ==> O$I@77caeb3e

jshell> class O { static class I {} }
Exception in thread "main" java.lang.ClassFormatError: class not in class file format
        at jdk.jdi/com.sun.tools.jdi.VirtualMachineImpl.redefineClasses(VirtualMachineImpl.java:396)
        at jdk.jshell/jdk.jshell.execution.JdiExecutionControl.redefine(JdiExecutionControl.java:90)
        at jdk.jshell/jdk.jshell.Unit.doRedefines(Unit.java:312)
        at jdk.jshell/jdk.jshell.Eval.lambda$compileAndLoad$27(Eval.java:1120)
        at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:178)
        at java.base/java.util.AbstractList$RandomAccessSpliterator.forEachRemaining(AbstractList.java:722)
        at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
        at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
        at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:575)
        at java.base/java.util.stream.AbstractPipeline.evaluateToArrayNode(AbstractPipeline.java:260)
        at java.base/java.util.stream.ReferencePipeline.toArray(ReferencePipeline.java:616)
        at java.base/java.util.stream.ReferencePipeline.toArray(ReferencePipeline.java:622)
        at java.base/java.util.stream.ReferencePipeline.toList(ReferencePipeline.java:627)
        at jdk.jshell/jdk.jshell.Eval.lambda$compileAndLoad$29(Eval.java:1121)
        at jdk.jshell/jdk.jshell.TaskFactory.lambda$runTask$4(TaskFactory.java:213)
        at jdk.compiler/com.sun.tools.javac.api.JavacTaskPool.getTask(JavacTaskPool.java:193)
        at jdk.jshell/jdk.jshell.TaskFactory.runTask(TaskFactory.java:206)
        at jdk.jshell/jdk.jshell.TaskFactory.compile(TaskFactory.java:186)
        at jdk.jshell/jdk.jshell.Eval.compileAndLoad(Eval.java:1100)
        at jdk.jshell/jdk.jshell.Eval.declare(Eval.java:901)
        at jdk.jshell/jdk.jshell.Eval.eval(Eval.java:140)
        at jdk.jshell/jdk.jshell.JShell.eval(JShell.java:513)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.processSource(JShellTool.java:3633)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.processSourceCatchingReset(JShellTool.java:1353)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.processInput(JShellTool.java:1251)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.run(JShellTool.java:1222)
        at jdk.jshell/jdk.internal.jshell.tool.JShellTool.start(JShellTool.java:1005)
        at jdk.jshell/jdk.internal.jshell.tool.JShellToolBuilder.start(JShellToolBuilder.java:261)
        at jdk.jshell/jdk.internal.jshell.tool.JShellToolProvider.main(JShellToolProvider.java:120)

There are two problems here (although the stack trace immediately only shows one of them):

Redefining Classes

When a snippet is redefined, JShell first tries to redefine it using JDI (VirtualMachine.redefineClasses). This usually throws UnsupportedOperationException is the redefine cannot happen, and JdiExecutionControl handles that gracefully. JShell will recompile and reload the given snippet, and dependent snippets, under different names.

But the redefineClasses method can also throw various LinkageErrors. These are properly documented for the method: https://docs.oracle.com/en/java/javase/25/docs/api/jdk.jdi/com/sun/jdi/VirtualMachine.html#redefineClasses(java.util.Map)

But JdiExecutionControl is not handling these LinkageErrors.

The proposed solution herein is to simply catch and handle the LinkageErrors in the same way as the UnsupportedOperationException (and other exceptions).

InnerClasses attribute data overriding information from sources

Consider situation when compiling the third input: class O { static class I {} }.

When this is being compiled, a classfile for var i = new O().new I(); exists, and its InnerClasses attribute records O.I to be a non-static inner class.

While compiling the code for class O { static class I {} }, the classfile for var i is also read from the classfile, and its InnerClasses attribute is read as well. And as a consequence, the O.I class will be marked as non-static, which conflicts with what is in the source file.

This is not related to JShell as such, it can be reproduced with javac. Please see the test/langtools/tools/javac/recovery/SourceAndInnerClassInconsistency.java test.

The proposal herein is to not use the information from the InnerClasses classfile attribute to manipulate classes that originate in a source file. More generally, I think the information from the source should always prevail over information from other/unrelated classfiles. Note the InnerClasses attribute is in a classfile that has no real relation to the source code that is being compiled, it is simply an classfile on the classpath.

/issue JDK-8368999

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⚠️ Found leading lowercase letter in issue title for 8340840: jshell ClassFormatError when making inner class static, 8368999: jshell crash when existing sealed class is updated to also be abstract

Issues

JDK-8340840: jshell ClassFormatError when making inner class static (Bug - P4)
JDK-8368999: jshell crash when existing sealed class is updated to also be abstract (Bug - P4)

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Maurizio Cimadamore (@mcimadamore - Reviewer)

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8368999: jshell crash when existing sealed class is updated to also be abstract

bridgekeeper · 2025-10-07T07:17:18Z

👋 Welcome back jlahoda! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2025-10-07T07:18:13Z

@lahodaj This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8340840: jshell ClassFormatError when making inner class static
8368999: jshell crash when existing sealed class is updated to also be abstract

Reviewed-by: mcimadamore

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 195 new commits pushed to the master branch:

1e5e17a: 8369590: LocaleEnhanceTest has incorrectly passing test case
28bf917: 8348844: Remove remaining JVMTI tests from ProblemList-Virtual, use requires instead
cc6f8f1: 8369997: Tests that use custom scheduler should use jdk.test.lib.thread.VThreadScheduler
... and 192 more: https://git.openjdk.org/jdk/compare/2bfada3f58df6c041d948267368cbc4db915cac3...master

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openjdk · 2025-10-07T07:18:58Z

@lahodaj
Adding additional issue to issue list: 8368999: jshell crash when existing sealed class is updated to also be abstract.

openjdk · 2025-10-07T07:19:35Z

@lahodaj The following label will be automatically applied to this pull request:

compiler

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2025-10-07T07:23:22Z

Webrevs

00: Full (6977a247)

liach · 2025-10-07T15:37:46Z

src/jdk.jshell/share/classes/jdk/jshell/execution/JdiExecutionControl.java

        } catch (EngineTerminationException ex) {
            throw ex;
-        } catch (Exception ex) {
+        } catch (Exception | LinkageError ex) {


How was ClassFormatError previously thrown here? Was it wrapped in some exception?

It was simply thrown out of the redefine method, as the stacktrace in the summary suggests. Note that the javadoc for redefineClasses is very clear it may throw ClassFormatError:
https://docs.oracle.com/en/java/javase/25/docs/api/jdk.jdi/com/sun/jdi/VirtualMachine.html#redefineClasses(java.util.Map)

mcimadamore · 2025-10-17T16:32:19Z

src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/ClassReader.java

-                if (c == outer && member.owner == c) {
-                    member.flags_field = flags;
-                    enterMember(c, member);
+                if ((member.flags_field & FROM_SOURCE) == 0) {


I agree with the fix -- I guess I'd slightly prefer to see a warning if a mismatch is detected, but I'll leave that to you.

mcimadamore

javac changes look good (did not look at the jshell part)

lahodaj added 3 commits October 6, 2025 19:37

8340840: jshell ClassFormatError when making inner class static

121d30b

8368999: jshell crash when existing sealed class is updated to also be abstract

Fixing test.

149b690

Updating copyright year.

6977a24

openjdk bot added the compiler [email protected] label Oct 7, 2025

openjdk bot added the rfr Pull request is ready for review label Oct 7, 2025

liach reviewed Oct 7, 2025

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lahodaj commented Oct 7, 2025 • edited by openjdk bot Loading Uh oh! There was an error while loading. Please reload this page.

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Redefining Classes

InnerClasses attribute data overriding information from sources

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