JaCoco MVN unknown block type

Question

So I'm using the JaCoco maven plugin to automatically generate code coverage reports so I can then send them to codecov to display on GitHub. All of a sudden I'm getting a build failure from JaCoco saying "Unknown block type". This wasn't happening the yesterday so I don't know why it happens now. Here is the relevant part of my pom.xml

<plugin>
  <groupId>org.jacoco</groupId>
  <artifactId>jacoco-maven-plugin</artifactId>
  <version>0.8.5</version>
  <executions>
    <execution>
      <goals>
        <goal>prepare-agent</goal>
      </goals>
    </execution>
    <execution>
      <id>report</id>
      <phase>test</phase>
      <goals>
        <goal>report</goal>
      </goals>
    </execution>
  </executions>
</plugin>

How do I fix this to properly generate coverage reports?

-X trace

[DEBUG] Configuring mojo org.jacoco:jacoco-maven-plugin:0.8.5:report from plugin realm ClassRealm[plugin>org.jacoco:jacoco-maven-plugin:0.8.5, parent: jdk.internal.loader.ClassLoaders$AppClassLoader@55054057]
[DEBUG] Setting property: classpath.resource.loader.class => 'org.codehaus.plexus.velocity.ContextClassLoaderResourceLoader'.
[DEBUG] Setting property: site.resource.loader.class => 'org.codehaus.plexus.velocity.SiteResourceLoader'.
[DEBUG] Setting property: velocimacro.messages.on => 'false'.
[DEBUG] Setting property: runtime.log.invalid.references => 'false'.
[DEBUG] Setting property: resource.loader => 'classpath,site'.
[DEBUG] Setting property: velocimacro.permissions.allow.inline.to.replace.global => 'true'.
[DEBUG] Setting property: resource.manager.logwhenfound => 'false'.
[DEBUG] *******************************************************************
[DEBUG] Starting Apache Velocity v1.5 (compiled: 2007-02-22 08:52:29)
[DEBUG] RuntimeInstance initializing.
[DEBUG] Default Properties File: org/apache/velocity/runtime/defaults/velocity.properties
[DEBUG] LogSystem has been deprecated. Please use a LogChute implementation.
[DEBUG] Default ResourceManager initializing. (class org.apache.velocity.runtime.resource.ResourceManagerImpl)
[DEBUG] ResourceLoader instantiated: org.codehaus.plexus.velocity.ContextClassLoaderResourceLoader
[DEBUG] ResourceLoader instantiated: org.codehaus.plexus.velocity.SiteResourceLoader
[DEBUG] ResourceCache: initialized (class org.apache.velocity.runtime.resource.ResourceCacheImpl)
[DEBUG] Default ResourceManager initialization complete.
[DEBUG] Loaded System Directive: org.apache.velocity.runtime.directive.Literal
[DEBUG] Loaded System Directive: org.apache.velocity.runtime.directive.Macro
[DEBUG] Loaded System Directive: org.apache.velocity.runtime.directive.Parse
[DEBUG] Loaded System Directive: org.apache.velocity.runtime.directive.Include
[DEBUG] Loaded System Directive: org.apache.velocity.runtime.directive.Foreach
[DEBUG] Created '20' parsers.
[DEBUG] Velocimacro : initialization starting.
[DEBUG] Velocimacro : allowInline = true : VMs can be defined inline in templates
[DEBUG] Velocimacro : allowInlineToOverride = true : VMs defined inline may replace previous VM definitions
[DEBUG] Velocimacro : allowInlineLocal = false : VMs defined inline will be global in scope if allowed.
[DEBUG] Velocimacro : autoload off : VM system will not automatically reload global library macros
[DEBUG] Velocimacro : Velocimacro : initialization complete.
[DEBUG] RuntimeInstance successfully initialized.
[DEBUG] Configuring mojo 'org.jacoco:jacoco-maven-plugin:0.8.5:report' with basic configurator -->
[DEBUG]   (f) dataFile = /mnt/a/Documents/school/college/courses/csci420/UMLEditor/target/jacoco.exec
[DEBUG]   (f) outputDirectory = /mnt/a/Documents/school/college/courses/csci420/UMLEditor/target/site/jacoco
[DEBUG]   (f) outputEncoding = UTF-8
[DEBUG]   (f) project = MavenProject: UMLEditor:UMLEditor:0.0.1-SNAPSHOT @ /mnt/a/Documents/school/college/courses/csci420/UMLEditor/pom.xml
[DEBUG]   (f) skip = false
[DEBUG]   (f) sourceEncoding = UTF-8
[DEBUG]   (f) title = UMLEditor
[DEBUG] -- end configuration --
[INFO] Loading execution data file /mnt/a/Documents/school/college/courses/csci420/UMLEditor/target/jacoco.exec
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  36.600 s
[INFO] Finished at: 2020-04-25T04:24:50-04:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.jacoco:jacoco-maven-plugin:0.8.5:report (report) on project UMLEditor: An error has occurred in JaCoCo report generation.: Error while creating report: Unknown block type 77. -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.jacoco:jacoco-maven-plugin:0.8.5:report (report) on project UMLEditor: An error has occurred in JaCoCo report generation.
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:215)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:566)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
Caused by: org.apache.maven.plugin.MojoExecutionException: An error has occurred in JaCoCo report generation.
    at org.jacoco.maven.AbstractReportMojo.execute (AbstractReportMojo.java:168)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:566)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
Caused by: org.apache.maven.reporting.MavenReportException: Error while creating report: Unknown block type 77.
    at org.jacoco.maven.AbstractReportMojo.executeReport (AbstractReportMojo.java:184)
    at org.jacoco.maven.AbstractReportMojo.execute (AbstractReportMojo.java:166)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:566)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
Caused by: java.io.IOException: Unknown block type 77.
    at org.jacoco.core.data.ExecutionDataReader.readBlock (ExecutionDataReader.java:119)
    at org.jacoco.core.data.ExecutionDataReader.read (ExecutionDataReader.java:93)
    at org.jacoco.core.tools.ExecFileLoader.load (ExecFileLoader.java:60)
    at org.jacoco.core.tools.ExecFileLoader.load (ExecFileLoader.java:74)
    at org.jacoco.maven.ReportSupport.loadExecutionData (ReportSupport.java:89)
    at org.jacoco.maven.ReportMojo.loadExecutionData (ReportMojo.java:61)
    at org.jacoco.maven.AbstractReportMojo.executeReport (AbstractReportMojo.java:178)
    at org.jacoco.maven.AbstractReportMojo.execute (AbstractReportMojo.java:166)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:566)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
[ERROR]
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

Answer 1

Unknown block type

during the execution of org.jacoco:jacoco-maven-plugin:0.8.5:report indicates corrupted jacoco.exec file.

This file is produced by JaCoCo agent at the termination of JVM with tests using JVM shutdown hook.

Corruption of file typically happens when JVM with tests is hard-killed instead of proper graceful successful termination.

my mvn hangs for quite some time after finishing the last test and doesn't seem to be doing anything

is IMO a confirmation that JVM with tests is not terminated gracefully, because this typically indicates that maven-surefire-plugin waits for termination of your tests for some time and then kills JVM - see similar issue https://github.com/jacoco/jacoco/issues/1042

All in all, please fix your code/tests - JVM with tests should terminate gracefully.

---

I also believe I have located the troublesome test file as when I exclude it everything runs fine and it even stops hanging. I just don't understand what would be wrong in that file that would cause a hang (there are no loops, the only "files" being done are modifying the default System.out/err streams to a separate print writer) given that most of it is string manipulation.

Quoting http://maven.apache.org/surefire/maven-surefire-plugin/faq.html for maven-surefire-plugin version 3.0.0-M4:

It would be even worse if you override the Java stream by System.setOut because the stream is also supposed to be corrupted but the Maven will never see the tests finished and build may hang.