fix(run): run single Java files whose main class is not the first top-level type (#1417)

A Java file outside a Maven / Gradle build ran as `java File.java` (JEP 330), which launches the file's first top-level type on JDK 21 and earlier. A file whose main is in a later class failed with "can't find main(String[]) method in class: Parent", and the gutter Run of a second or nested class's main launched the first class. Such files now compile with the JDK's own `javac -g -d <class dir>` and run `java -cp <class dir> <main class>`; a main in the first class, and compact source files, still use the source launcher. Debug passes the JDWP agent through JDK_JAVA_OPTIONS, which only the java launcher reads.

Co-authored-by: ldg030201 <[email protected]>

src/features/run/javaDebug.ts

@@ -40,8 +40,12 @@ function withProperty(args: readonly string[], key: string, value: string): stri
 export function jdwpLaunch(config: RunConfig): RunConfig | null {
   if (config.kind === "tomcat") return { ...config, params: { ...config.params, tomcatDebug: "true" } };
   const args = config.args;
-  // A single source file (`java Hi.java`): the agent goes before the file.
-  if (config.kind === "java-file") return { ...config, args: [JDWP_AGENT, ...args] };
+  // A single source file (`java Hi.java`): the agent goes before the file. Compiled first
+  // (`javac … && java -cp …`): through `JDK_JAVA_OPTIONS`, which only the `java` launcher reads.
+  if (config.kind === "java-file")
+    return args.length
+      ? { ...config, args: [JDWP_AGENT, ...args] }
+      : { ...config, env: withOption(config.env, "JDK_JAVA_OPTIONS", JDWP_AGENT) };
   if (config.kind === "maven" || /(^|\/)mvnw?(\.cmd)?$/.test(config.command)) {
     if (args.some((a) => a === "spring-boot:run" || /:spring-boot-maven-plugin:[^:]*:run$/.test(a)))
       return { ...config, args: withProperty(args, "spring-boot.run.jvmArguments", JDWP_AGENT) };