feat:Spoon agent

[nharrand]

With the help of IncrementalLauncher and Decompiler, we can propose an abstraction of java standard ClassFileTransformer interface that let an user define Spoon transformations applied on bytecode at load time.

Every time a class is loaded:

• if it matches a filter
• it is decompiled
• its decompiled sources are added to the Spoon Model
• users transformation are applied on the new CtType
• the type is recompiled
• loading resumres

[monperrus]

This is a pretty neat and unconventional usage of Spoon, I like it :-)

[zielint0]

I think it may have an enormous potential of practical uses!

[nharrand]

Currently this only includes a ClassFileTransformer abstraction, which allows user to implements agent. But may be we should add something similar to Launcher with a real premain that actually load Processor(s) and apply them. A RuntimeLauncher if you will.

WDYT?

[pvojtechovsky]

I guess all the members above should be private or at least protected. WDYT?

[nharrand]

Yes definitly.

[pvojtechovsky]

Nice idea!

I have few comments to design. Actually client has to extend SpoonClassFileTransformer and must implement two methods.
Problems:

• client has to implement accept even if s/he doesn't need filter.
• if client extends wrong methods then it will not work

May be it would be nicer if

• SpoonClassFileTransformer would have method setTransformer(ClassTransformer) ... or ClassTransfomer might be a new constructor parameter.
• ClassTransformer would be interface with 2 methods: transform(CtType) and boolean accept(CtType)
• boolean accept(CtType) would be marker default with body return true;
• optionally there might be method SpoonClassFileTransformer#setFilter(Filter<? super CtType>), which would allow to define extra type filter too.

Then all the implementation can be done by lambda expressions

[nharrand]

@pvojtechovsky Seems like good ideas. I'll try to implement them.

[monperrus]

Thanks a lot for this potentially game-changing PR.