Consider code like:
---
class C {
    void m
    {
        return;
    }
}
---

And compile it like:
---
 $ javac -XDshould-stop.at=FLOW -XDdev /tmp/C.java
/tmp/C.java:3: error: '(' expected
    {
    ^
1 error
An exception has occurred in the compiler (19.0.1-internal). Please file a bug against the Java compiler via the Java bug reporting page (http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program, the following diagnostic, and the parameters passed to the Java compiler in your report. Thank you.
java.lang.AssertionError
        at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
        at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$AliveAnalyzer.clearPendingExits(Flow.java:589)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$AliveAnalyzer.visitClassDef(Flow.java:544)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:810)
        at jdk.compiler/com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:447)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$AliveAnalyzer.analyzeTree(Flow.java:1082)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$AliveAnalyzer.analyzeTree(Flow.java:1074)
        at jdk.compiler/com.sun.tools.javac.comp.Flow.analyzeTree(Flow.java:223)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.flow(JavaCompiler.java:1377)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.flow(JavaCompiler.java:1351)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:946)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:317)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:176)
        at jdk.compiler/com.sun.tools.javac.Main.compile(Main.java:64)
        at jdk.compiler/com.sun.tools.javac.Main.main(Main.java:50)
printing javac parameters to: /home/jlahoda/src/jdk/jdk/javac.20230201_094507.args
---

The reason is that the returnResult is set in Attr.visitErroneous, but not cleared, and so an error is not produced for the return, leading to the assert failure in Flow.

This then may lead to various JShell problems, as JShell runs with -XDshould-stop.at=FLOW.