sbt unnecessarily copies local dependencies to staging

[jakajancar]

SBT copies local dependencies to a staging directory if their source directory is not writable. I do not think this should be required if the targetDirectory of those dependencies is outside the source directory.

Shouldn't the targetDirectory be checked for writability instead?

[duboisf]

I don't understand, can you elaborate? What's the problem you're having?

[jakajancar]

Several projects in a read-only source tree with target set to writable directories:

src/projecta      -> build/projecta
src/projectb      -> build/projectb
src/projectc      -> build/projectc
src/commonproject -> build/commonproject

project{a,b,c} depend on commonproject.

When projecta is built, the referenced code determines that src/commonproject is not writable and copies it to staging. This is completely unnecessary, though.

[duboisf]

So build/commonproject is writable?

[jakajancar]

Exactly, all the build directories are, src aren't.

(the use-case is developing with Docker: source r/o mounted from the host, build/run in the container).

[duboisf]

OK, I agree that it should not copy the project if targetDirectory is writable.

[duboisf]

Actually, having thought a bit more, this won't work in every situation. For example, I have projects that generate source files somewhere under the baseDirectory, which in your case is read-only. So even if target is writable, this won't work.

[jakajancar]

That's pretty weird I think. By that logic you could also copy baseDirectory/.., because what if you generate files in a sibling of the baseDirectory, or some other completely unrelated directory.

But anyway, I see it would be a regression. I will find a way to change this only for myself.

[jakajancar]

@duboisf So now that we are also moving development (not just test/prod) to a read-only source tree, this is even a bigger problem:

Changes to source files are not detected unless you manually delete staging before every compile.