Classloader not used for source code loading

[jkamon]

GWT compiler uses classloader of executing thread. Such implementation provides great flexibility of callers to provide new possibilities of loading resources. Compilation with custom classloader could enable loading of artefacts not only from local paths but also from absolute paths or other locations or memory.
Due to the implementation of ResourceLoaders there is no way to fully utilize classloader and for example load sources from any location desired. Limitation comes from:

gwt/dev/core/src/com/google/gwt/dev/cfg/ResourceLoaders.java

Line 59 in 5935a97

Sets.newLinkedHashSet(Splitter.on(File.pathSeparatorChar).split(JAVA_CLASS_PATH.value()));

since only system classpath will be scanned for artefacts.

There are probably several ways to lift this limitation:
a) Simple property adding new locations to classpathentries would probably help.
b) Ability to provide own implementation of resource loader could be a cleaner way
and someone with better understanding of GWT architecture would probably generate better options.

[niloc132]

Thanks for starting this discussion - can I ask you to talk a little more about your use case?

I used to run a web service that compiled projects edited through a browser UI, and ended up needing that kind of abstraction. The problem is that the compiler isn't terribly easy to use that way, its really intended to be run in its own JVM via main() methods and communicate through the filesystem, logs, and exit(code) when complete. This makes it a little hard to plug in new implementations of various interfaces besides just providing paths via -src or -classpath.

Digging deeper into ResourceLoaders... unfortunately the static fromContextClassLoader() method is called in many places (with forPathAndFallback(...) being used just for SDM). There are assumptions made about this, and remarks about how it should not be this way, but this fact does make it so that the task is harder than it should be.

It is worth doing, worth getting right... but it might also be worth discussing your goals briefly, to see if there isn't a more expedient way to achieve them?