RFR: 8306914: Implementation of JEP Launch Multi-File Source-Code Programs [v4]

[Alan Bateman]

On Wed, 25 Oct 2023 11:02:41 GMT, Christian Stein <cstein at openjdk.org> wrote:

>> Please review this change set implementing [JEP 458](https://openjdk.org/jeps/458) "Launch Multi-File Source-Code Programs" by introducing a new entry-point `SourceLauncher` in package `com.sun.tools.javac.launcher` of module `jdk.compiler`. The former `Main` entry-point is kept as-is in order to preserve (and possibly fall back to) existing behaviour of launching single-file source-code programs.
>> 
>> The code of the new entry-point and other new classes introduced by this pull request is based on the original implementation. It extends it to dynamically resolve required types "on-the-fly" using an in-memory class loader capable to compile Java source files - applying a strict name-based pattern as described in the JEP.
>> 
>> To support modular programs with user-provided additional modules (launched for example via `java -p . pkg/Prog1.java`) `ALL-MODULE-PATH` is now also part of the implicit list of modules name in source launch mode.
>> 
>> ### Open Ends
>> 
>> - [ ] Tests with [JEP ?: Implicitly Declared Classes and Instance Main Method (2nd Preview)](https://bugs.openjdk.org/browse/JDK-8315398)
>> 
>> ### OpenJDK's Demo Programs
>> 
>> OpenJDK's demo programs can be found in the [src/demo/share/jfc](https://github.com/openjdk/jdk/tree/master/src/demo/share/jfc) directory. These multi-file source-code programs can be launched via `java ${PROGRAM}` once this implementation is integrated; with `${PROGRAM}` being one of the following files:
>> 
>> - [x] `src/demo/share/jfc/CodePointIM/CodePointIM.java`
>> - [x] `src/demo/share/jfc/FileChooserDemo/FileChooserDemo.java`
>> - [x] `src/demo/share/jfc/Font2DTest/Font2DTest.java`
>> - [x] `src/demo/share/jfc/J2Ddemo/java2d/J2Ddemo.java`
>> - [x] `src/demo/share/jfc/Metalworks/Metalworks.java`
>> - [x] `src/demo/share/jfc/Notepad/Notepad.java`
>> - [x] `src/demo/share/jfc/SampleTree/SampleTree.java`
>> - [ ] `src/demo/share/jfc/Stylepad/Stylepad.java` — requires `src/demo/share/jfc/Notepad/Notepad.java`
>> - [x] `src/demo/share/jfc/SwingSet2/SwingSet2.java`
>> - [ ] `src/demo/share/jfc/TableExample/TableExample.java` — requires a database driver on the class path
>> - [ ] `src/demo/share/jfc/TableExample/TableExample2.java` —  requires a database driver on the class path
>> - [x] `src/demo/share/jfc/TableExample/TableExample3.java`
>> - [x] `src/demo/share/jfc/TableExample/TableExample4.java`
>> - [x] `src/demo/share/jfc/TransparentRuler/transparentruler/Ruler.java`
>
> Christian Stein has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Main method determines the main class now

src/jdk.compiler/share/classes/com/sun/tools/javac/launcher/MemoryContext.java line 238:

> 236:         var memoryConfig = parentLayer.configuration().resolveAndBind(memoryFinder, ModuleFinder.of(), Set.of(applicationModule.name()));
> 237:         var memoryClassLoader = new MemoryClassLoader(inMemoryClasses, parentLoader, applicationModule, descriptor, this::compileJavaFileByName);
> 238:         var memoryController = ModuleLayer.defineModules(memoryConfig, List.of(parentLayer), __ -> memoryClassLoader);

It would be helpful if the comment were expanded to explain why memoryClassLoader is needed here. ClassLoaders created by the defineModulesXXX methods are capable to loading modules in memory file systems, the issue is the dynamic compilation (I think).

src/jdk.compiler/share/classes/com/sun/tools/javac/launcher/MemoryContext.java line 246:

> 244:         memoryController.addOpens(module, mainClassNamePackageName, getClass().getModule());
> 245: 
> 246:         return memoryLayer.findLoader(applicationModule.name()).loadClass(mainClassName);

The defining class loader for the main class will be memoryClassLoader, right?

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PR Review Comment: https://git.openjdk.org/jdk/pull/13712#discussion_r1371789699
PR Review Comment: https://git.openjdk.org/jdk/pull/13712#discussion_r1371785140