Ensure correct runtime Java is used when it matches build Java (#110730)

Ensures that the value provided by the `runtime.java` system property,
or `RUNTIME_JAVA_HOME` environment variable is respected, even when it
is the same as the current `JAVA_HOME`. The previous logic had
`isRuntimeJavaHomeSet` return `false` when the "requested" Java was the
same as the current one. This isn't strictly correct, as the behavior
when Java home is unset is to use the bundled JDK. The result was that
passing `-Druntime.java=17` when the Gradle daemon was also using Java
17 was to execute tests with the bundled JDK, which could be something
entirely different.

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/info/GlobalBuildInfoPlugin.java

@@ -51,6 +51,7 @@ import java.time.ZonedDateTime;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Locale;
+import java.util.Optional;
 import java.util.Random;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Collectors;
@@ -97,24 +98,25 @@ public class GlobalBuildInfoPlugin implements Plugin<Project> {
         JavaVersion minimumCompilerVersion = JavaVersion.toVersion(getResourceContents("/minimumCompilerVersion"));
         JavaVersion minimumRuntimeVersion = JavaVersion.toVersion(getResourceContents("/minimumRuntimeVersion"));
 
-        File runtimeJavaHome = findRuntimeJavaHome();
-        boolean isRuntimeJavaHomeSet = Jvm.current().getJavaHome().equals(runtimeJavaHome) == false;
+        Optional<File> selectedRuntimeJavaHome = findRuntimeJavaHome();
+        File actualRuntimeJavaHome = selectedRuntimeJavaHome.orElse(Jvm.current().getJavaHome());
+        boolean isRuntimeJavaHomeSet = selectedRuntimeJavaHome.isPresent();
 
         GitInfo gitInfo = GitInfo.gitInfo(project.getRootDir());
 
         BuildParams.init(params -> {
             params.reset();
-            params.setRuntimeJavaHome(runtimeJavaHome);
+            params.setRuntimeJavaHome(actualRuntimeJavaHome);
             params.setJavaToolChainSpec(resolveToolchainSpecFromEnv());
             params.setRuntimeJavaVersion(
                 determineJavaVersion(
                     "runtime java.home",
-                    runtimeJavaHome,
+                    actualRuntimeJavaHome,
                     isRuntimeJavaHomeSet ? minimumRuntimeVersion : Jvm.current().getJavaVersion()
                 )
             );
             params.setIsRuntimeJavaHomeSet(isRuntimeJavaHomeSet);
-            JvmInstallationMetadata runtimeJdkMetaData = metadataDetector.getMetadata(getJavaInstallation(runtimeJavaHome));
+            JvmInstallationMetadata runtimeJdkMetaData = metadataDetector.getMetadata(getJavaInstallation(actualRuntimeJavaHome));
             params.setRuntimeJavaDetails(formatJavaVendorDetails(runtimeJdkMetaData));
             params.setJavaVersions(getAvailableJavaVersions());
             params.setMinimumCompilerVersion(minimumCompilerVersion);
@@ -298,19 +300,19 @@ public class GlobalBuildInfoPlugin implements Plugin<Project> {
         }
     }
 
-    private File findRuntimeJavaHome() {
+    private Optional<File> findRuntimeJavaHome() {
         String runtimeJavaProperty = System.getProperty("runtime.java");
 
         if (runtimeJavaProperty != null) {
-            return resolveJavaHomeFromToolChainService(runtimeJavaProperty);
+            return Optional.of(resolveJavaHomeFromToolChainService(runtimeJavaProperty));
         }
         String env = System.getenv("RUNTIME_JAVA_HOME");
         if (env != null) {
-            return new File(env);
+            return Optional.of(new File(env));
         }
         // fall back to tool chain if set.
         env = System.getenv("JAVA_TOOLCHAIN_HOME");
-        return env == null ? Jvm.current().getJavaHome() : new File(env);
+        return env == null ? Optional.empty() : Optional.of(new File(env));
     }
 
     @NotNull