SocketLaunchingConnectorImpl#launch emits legacy JPDA flags on modern JDKs

[systemhalted]

SocketLaunchingConnectorImpl#launch currently constructs the debuggee command line by unconditionally adding the legacy JPDA launch sequence:

   // SocketLaunchingConnectorImpl.java:204-205
   execString += " -Xdebug -Xnoagent -Djava.compiler=NONE";
   execString += " -Xrunjdwp:transport=dt_socket,address=" + address
               + ",server=n,suspend=" + (fSuspend ? "y" : "n");

On JDK 21, this produces the following warning on every debugger launch:

   OpenJDK 64-Bit Server VM warning: The java.compiler system property
   is obsolete and no longer supported, use -Xint

On JDK 23, the situation is worse: -Xnoagent is no longer recognized
and the debuggee fails to start outright with Unrecognized option: -Xnoagent. The standard JDI launching connector therefore does not
work on a current JDK.

For JDK 5 and later, the supported debug-agent form is:

   -agentlib:jdwp=transport=dt_socket,address=...,server=n,suspend=...

The other options are not needed for modern debugging:

1. -Xdebug is a compatibility option that has been ignored on modern
   JDKs and was deprecated for removal in JDK 22.
2. -Xnoagent has been ignored for many releases, was deprecated for
   removal in JDK 22, and is rejected outright in JDK 23.
3. -Djava.compiler=NONE is obsolete on JDK 13+, emits the warning
   above, and no longer selects interpreted-only execution. If
   interpreted-only execution is desired, the supported option is
   -Xint.

• The sibling launcher path StandardVMDebugger#runVMArguments
  (org.eclipse.jdt.launching/.../StandardVMDebugger.java:196-214)
  already gates the legacy options by Java version and prefers
  -agentlib:jdwp=... for Java 5 and later.

• The PR Fix warnings during JDI tests run #511 in this repo fixed the same warning by JDK-gating the legacy emit, but only in the JDI test infrastructure
  (org.eclipse.jdt.debug.jdi.tests/.../AbstractJDITest.java).
  SocketLaunchingConnectorImpl#launch was not updated.

  • [critical] Fail to debug with java 23 - Unrecognized option: -Xnoagent microsoft/java-debug#561 → #562: Microsoft's parallel launcher path
    hit the same JDK 23 breakage and patched it.

  Suggested fix: replace lines 204-205 with

   execString += " -agentlib:jdwp=transport=dt_socket,address=" + address
               + ",server=n,suspend=" + (fSuspend ? "y" : "n");
  

  -agentlib:jdwp= has been supported since JDK 5, so no version gating
  is required. Alternatively, mirror StandardVMDebugger by detecting
  the target JDK version and gating the
  legacy emit accordingly.

  Reproduction

  • Editor: Emacs 30.x with dap-mode + lsp-java; JDT LS server bundle
    org.eclipse.jdt.debug 3.25.100.v20260212-0641,
    jdimodel.jar from bundle org.eclipse.jdt.debug.jdi.
  • Target JDK tested: Eclipse Temurin 21.0.11 (reproduces the warning).
    JDK 23 hard-failure mode is documented via JDK-8312072 not re-reproduced here.
  • Action: M-x dap-java-debug on a trivial Maven project with a public
    static void main(String[]).

  Captured debuggee command line:

   java -Xdebug -Xnoagent -Djava.compiler=NONE \
        -Xrunjdwp:transport=dt_socket,address=localhost:<port>,server=n,suspend=y \
        -cp <classpath> <main>