Hello @cjohnstoniv, Can you provide an example code to reproduce the above error. Thanks! Unfortunately not easily as the code base we build this on is private and I cannot share it. Also it's built using a localjdk workspace config so none of that would be repeatable on anyone else's machine (unless they have java in the same path).

The issue is quite straightforward / obvious though. The `Optional.isEmpty` method was added in Java 9+ so it would (as expected) fail in any Java 8 JVMs. My ask is can we just make this 1 line Java 8 compliant by making it `!optional.isPresent()` instead.

If Bazel still intends to support Java 8+ then this would be a requirement to make sure that the coverage tools remain Java 8 compliant. Unless the intention is Java 8+ compilation and not runtime.

This all works just fine on Bazel 5.4.0 and if you look at the diffs between 5.4.0 and 6.0.0, you can see this class updated to Java 9+ only complaint code. I personally don't see a reason not to make this one line compatible with Java 8. But even if you are *targeting* Java 8, I would expect the coverage tool to be built in the `exec` configuration and (by default) use a remote JDK 11. Using a more modern JDK just for tools could help you in the meantime.  We want to run our runtime on Java 8 too as unfortunately our org still has a lot of software still running on Oracle Java 8 JDKs (gross, I know). So from a Bazel build/test perspective we are trying to keep it all as consistent as possible. Testing with Java 11 runtime but with Java 8 target, isn't the same as compiling and testing on the same JDK version. There are plenty of things like needing to add-opens/exports to make Java 8 compiled code run in Java 11 runtimes.

If the answer is the devs don't feel making this Java 8 compatible is the right thing to do, then we should update the docs to make it clear that Java 8 is supported purely from compilation and not from runtime. I don't mean "compile with Java 11, run with Java 8". What I am referring to is using something like `--java_runtime_version=local_jdk_8 --tool_java_runtime_version=remotejdk_11` to:
* build and test all regular targets with JDK 8
* build and execute tools run as part of the build itself (for example the coverage tools) with JDK 11

@cjohnstoniv Could you share at least the parts of your `.bazelrc` and `WORKSPACE` that configure Java toolchains?

 .bazelrc

```
build --embed_label=9.0.LTS-SNAPSHOT
build --java_language_version=8
build --tool_java_language_version=11
build --tool_java_runtime_version=remotejdk_11
build --java_runtime_version=localjdk_8
build --verbose_failures
build --experimental_ui_max_stdouterr_bytes=100048576
startup --max_idle_secs=300
test --test_output=errors
test --test_verbose_timeout_warnings
coverage --collect_code_coverage
coverage --combined_report=lcov
coverage --coverage_report_generator=@bazel_aladdin//sonarqube:SonarQubeCoverageGenerator
build --remote_cache=grpc://[SOME IP]:8980
build --remote_max_connections=200
coverage --experimental_split_coverage_postprocessing
coverage --experimental_fetch_all_coverage_outputs
build --disk_cache=/Users/chjohnst/mazel/.cache
```

WORKSPACE toolchains:

```
load("@bazel_tools//tools/jdk:local_java_repository.bzl", "local_java_repository")

local_java_repository(
  name = "localjdk",
  version = '8',
  java_home = "/Library/Java/JavaVirtualMachines/jdk1.8.0_202.jdk/Contents/Home"
)
```

@fmeum based on your comments above, I was under the impression that using `--tool_java_language_version=11 --tool_java_runtime_version=remotejdk_11` would have solved the issue (before we had --tool_java_language_version=8 --tool_java_runtime_version=remotejdk_11). But I still see the same error in the test logs:

Exception in thread "Thread-0" java.lang.NoSuchMethodError: java.util.Optional.isEmpty()Z
        at com.google.testing.coverage.JacocoLCOVFormatter$1.getExecPathForEntryName(JacocoLCOVFormatter.java:73)
        at com.google.testing.coverage.JacocoLCOVFormatter$1.visitBundle(JacocoLCOVFormatter.java:117)
        at com.google.testing.coverage.JacocoCoverageRunner.createReport(JacocoCoverageRunner.java:156)
        at com.google.testing.coverage.JacocoCoverageRunner.create(JacocoCoverageRunner.java:132)
        at com.google.testing.coverage.JacocoCoverageRunner$2.run(JacocoCoverageRunner.java:568)
GCov does not exist at the given path: ''
 If that also doesn't work I am personally out of ideas why you are seeing this issue. team-Rules-Java can probably help here. I'll see if I can find some time later this week from my personal PC to upload a small Java project that recreates the issue so others can test.

Oddly when I think about it, I would've expected the tools compilation stage to fail when I had set `--tool_java_language_version=8` as it would have tried compiling Java 11 code on Java 8; but instead it fails with a runtime NoSuchMethodError which suggests the tool is compiling on Java 11+ but for whatever reason is not running on Java 11+. [broken-java8-coverage.zip](https://github.com/bazelbuild/bazel/files/10460205/broken-java8-coverage.zip)

Attached is a sample project that recreates the issue following the following steps (assumes you downloaded the zip to an empty dir, also assumes linux OS, modify the less location for other OS's, you may also have to modify your Java 8 localjdk location in WORKSPACE file):

`unzip broken-java8-coverage.zip; bazelisk coverage //...; less bazel-out/k8-fastbuild/testlogs/unit-tests/test.log`

You will see that despite the tool java level and runtime being 11, the test runner still fails to calculate coverage due to the Java 9+ added Optional method. Also not sure if anyone has any experience with the Bazel distribution build but I tried checking out the 6.0 tag and compiling my own version of Bazel with changes to the JacocoLCOVFormatter class; however I found that seemingly when I run `compile.sh` and/or `bazel build //src:bazel` my changes to the class aren't picked up. I've confirmed this at least by making non-compilable changes to the class (i.e bad characters) and the bazel build runs just fine.

Is there someway I can rebuild/retest the JacocoLCOVFormatter class? I was trying to test what would happen if we made the `isEmpty()` call `!isPresent()` instead. @cushon This may he another instance of https://github.com/bazelbuild/bazel/issues/17281: The tool Java language level/runtime version not behaving as one may expect. Could you also provide some insight for this particular situation? @comius 

I can reproduce (thanks for https://github.com/bazelbuild/bazel/issues/17165#issuecomment-1397472443)!

```
Exception in thread "Thread-0" java.lang.NoSuchMethodError: java.util.Optional.isEmpty()Z
        at com.google.testing.coverage.JacocoLCOVFormatter$1.getExecPathForEntryName(JacocoLCOVFormatter.java:73)
...
        at com.google.testing.coverage.JacocoCoverageRunner$2.run(JacocoCoverageRunner.java:568)
```

It looks like `JacocoCoverageRunner` is being built in the exec configuration, and then apparently being run in the target configuration as part of test execution:

https://github.com/bazelbuild/bazel/blob/834ba08f9e780810743ff8eb39b125c0bf9e36b6/src/main/java/com/google/devtools/build/lib/rules/java/JavaToolchainRule.java#L279-L287

I'm not sure what the intent there was, but either it shouldn't be running on the target JDK, or it should be built in the target configuration. In Bazel `JacocoCoverageRunner` appears to be taken from `remote_coverage_tools` in precompiled form, but the packaging process probably uses JDK 11 with `-target 8`, which doesn't catch this. Is there any thoughts to a solution for this? Can we not just make the coverage tool's code Java 8 compliant so we know it will run in Java 8 JVM? This is assuming the isEmpty() usage is the only place we use Java 11+ code, but I also imagine there aren't any real needs for Java 11+ code other than "nice-to-haves". https://github.com/bazelbuild/bazel/pull/17338 is in review and fixes this. @cushon Can you say whether Ivo's input is truly needed? He appears to be quite busy.

It's unfortunately hard to cover with tests as that would require maintaining a JDK 8 on all CI machine. But if this breaks in the future, it can probably be fixed again as long as Java 8 is supported. I still get this issue on 6.1.0, the project above still recreates this issue. Rules requires a Java tools update and it's possible that didn't make it into the release.

@hvadehra Is there already a release with the change? https://github.com/bazelbuild/java_tools/releases/tag/java_v11.12 was released a few days ago which should contain https://github.com/bazelbuild/bazel/commit/c26665102d0d524bb42be8cd205c7b31a22a75c9 So can we reopen this issue then? It seems that even if the patch did go out, it's not actually fixing the issue defined here/demonstrated by the example. The fix went into the Java tools, but the commit bumping the pinned version of these tools didn't go into 6.1.0. It does look like it will be cherry-picked into 6.2.0. @cjohnstoniv You should be able to manually update remote_java_tools to v11.12 in your WORKSPACE too.
Bazel 6.0.0 Java 8 Coverage Broken
### Description of the bug:


When building with Bazel 6.0.0 and building a Java 8 (compile + runtime, with a local JDK setup) workspace fails to calculate any coverage.

There error I see in the test logs is:

Exception in thread "Thread-0" java.lang.NoSuchMethodError: java.util.Optional.isEmpty()Z
        at com.google.testing.coverage.JacocoLCOVFormatter$1.getExecPathForEntryName(JacocoLCOVFormatter.java:73)
        at com.google.testing.coverage.JacocoLCOVFormatter$1.visitBundle(JacocoLCOVFormatter.java:117)
        at com.google.testing.coverage.JacocoCoverageRunner.createReport(JacocoCoverageRunner.java:156)
        at com.google.testing.coverage.JacocoCoverageRunner.create(JacocoCoverageRunner.java:132)
        at com.google.testing.coverage.JacocoCoverageRunner$2.run(JacocoCoverageRunner.java:568)

### What's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.


Execute `bazel coverage` on any Java 8 (with a local OpenJDK 8 setup) workspace and look at the coverage files, they are empty.

### Which operating system are you running Bazel on?


Mac & Linux

### What is the output of `bazel info release`?


release 6.0.0

### If `bazel info release` returns `development version` or `(@non-git)`, tell us how you built Bazel.


_No response_

### What's the output of `git remote get-url origin; git rev-parse master; git rev-parse HEAD` ?


_No response_

### Have you found anything relevant by searching the web?

_No response_

### Any other information, logs, or outputs that you want to share?

Is JacocoLCOVFormatter only Java 11 supported now? Is there any way that maybe we can just change it to use `!optional.isPresent()` to make it Java 8 compatible?
src/main/java/com/google/devtools/build/lib/rules/java/JavaToolchainRule.java
src/main/java/com/google/devtools/build/lib/rules/java/JavaToolchainRule.java
src/java_tools/junitrunner/java/com/google/testing/coverage/JacocoLCOVFormatter.java
diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/JavaToolchainRule.java b/src/main/java/com/google/devtools/build/lib/rules/java/JavaToolchainRule.java
index ad4de48f61a6bb..594b6a76276941 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/JavaToolchainRule.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/JavaToolchainRule.java
@@ -282,8 +282,6 @@ The Java target version (e.g., '6' or '7'). It specifies for which Java runtime
         <!-- #END_BLAZE_RULE.ATTRIBUTE --> */
         .add(
             attr("jacocorunner", LABEL)
-                // This needs to be in the execution configuration.
-                .cfg(ExecutionTransitionFactory.create())
                 .allowedFileTypes(FileTypeSet.ANY_FILE)
                 .exec())
         /* <!-- #BLAZE_RULE(java_toolchain).ATTRIBUTE(proguard_allowlister) -->

diff --git a/src/java_tools/junitrunner/java/com/google/testing/coverage/JacocoLCOVFormatter.java b/src/java_tools/junitrunner/java/com/google/testing/coverage/JacocoLCOVFormatter.java
index b2c2bc58c31de6..53e62cdf3fe7f7 100644
--- a/src/java_tools/junitrunner/java/com/google/testing/coverage/JacocoLCOVFormatter.java
+++ b/src/java_tools/junitrunner/java/com/google/testing/coverage/JacocoLCOVFormatter.java
@@ -70,7 +70,7 @@ public IReportVisitor createVisitor(
       private Map<String, ISourceFileCoverage> sourceToFileCoverage = new TreeMap<>();
 
       private String getExecPathForEntryName(String classPath) {
-        if (execPathsOfUninstrumentedFiles.isEmpty()) {
+        if (!execPathsOfUninstrumentedFiles.isPresent()) {
           return classPath;
         }
 
