AssertionError while parsing unclosed class declarations

My colleague Eddie Aftandilian discovered the following crash, in which a syntax error causes the compiler to assert that it has fallen into an infinite loop.

It does not repro in 8, but it does repro in all javac versions > 8, including 15-ea. It only repros with annotation processing enabled, but it doesn't matter what the annotation processor actually does.

=== EmptyProcessor.java
import java.util.Set;
import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.RoundEnvironment;
import javax.lang.model.element.TypeElement;

public class EmptyProcessor extends AbstractProcessor {
  @Override
  public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
    return false;
  }
}
=== Repro.java
public class Repro {
  private static final ImmutableSetMultimap<String, Class<?>>
      MY_MAP =
          ImmutableSetMultimap.<String, Class<?>>builder()
              .putAll(
                  "foo") // syntax error
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class,
                  String.class)
              .build();
}
===
$ javac -fullversion
javac full version "15-ea+2-44"
$ javac EmptyProcessor.java
$ javac -processor EmptyProcessor Repro.java
An exception has occurred in the compiler (15-ea). 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.parser.JavacParser.reportSyntaxError(JavacParser.java:443)
        at jdk.compiler/com.sun.tools.javac.parser.JavacParser.reportSyntaxError(JavacParser.java:424)
        at jdk.compiler/com.sun.tools.javac.parser.JavacParser.accept(JavacParser.java:465)
        at jdk.compiler/com.sun.tools.javac.parser.JavacParser.accept(JavacParser.java:454)
        at jdk.compiler/com.sun.tools.javac.parser.JavacParser.classInterfaceOrRecordBody(JavacParser.java:3983)
        at jdk.compiler/com.sun.tools.javac.parser.JavacParser.classDeclaration(JavacParser.java:3715)
        at jdk.compiler/com.sun.tools.javac.parser.JavacParser.classOrRecordOrInterfaceOrEnumDeclaration(JavacParser.java:3657)
        at jdk.compiler/com.sun.tools.javac.parser.JavacParser.typeDeclaration(JavacParser.java:3646)
        at jdk.compiler/com.sun.tools.javac.parser.JavacParser.parseCompilationUnit(JavacParser.java:3490)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.parse(JavaCompiler.java:639)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.parse(JavaCompiler.java:676)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.parseFiles(JavaCompiler.java:1031)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.parseFiles(JavaCompiler.java:1018)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:938)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:316)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:176)
        at jdk.compiler/com.sun.tools.javac.Main.compile(Main.java:57)
        at jdk.compiler/com.sun.tools.javac.Main.main(Main.java:43)