proposal: cmd/go: allow replacing a subdirectory within a package

[nhooyr]

Right now, the replace directive only allows replacing modules with different modules.

It'd be nice if you could just replace a single sub package within a module with a different package elsewhere in a different module.

My use case is that right now goimports does not support reordering imports when there are multiple groups (#20818) and so I forked golang.org/x/tools.

Right now, I have to replace the entire module with my fork. I only modified golang.org/x/tools/imports so I only want to replace that package with the package from my fork. I don't want to maintain my fork and keep it up to date to use new additions to golang.org/x/tools. I only want to maintain the golang.org/x/tools/imports package.

[katiehockman]

I'm not sure that's the right approach here, since the go.mod files define module paths not packages. Allowing replace directives at the package level within a go.mod file seems a bit strange to me.

/cc @bcmills

[bcmills]

The term “module” as applied to software development is a self-contained unit of code. We specify module requirements at the granularity of individual modules, so it's not at all obvious to me how a replacement for only part of a module would interact with requirement resolution.

As a proposal, this would need a lot more detail, and even then I think it's unlikely that the marginal value would outweigh the increase in complexity (both for users and in the implementation).

For this concrete case, #20818 is still marked as Proposal-Approved. Is there a reason you cannot contribute your fixes upstream?

[nhooyr]

Sounds fine to me.

For this concrete case, #20818 is still marked as Proposal-Approved. Is there a reason you cannot contribute your fixes upstream?

No, just wanted to use it immediately without changing all import paths.